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“Education is not the learning of many facts but the training of the mind to think.” – Albert Einstein
To all Acadecers, Decathletes, and lovers of learning: I welcome you to the wonderful world of energy
science that awaits you within the pages of this year’s Science Power Guide. Covering topics as diverse
as quantum physics, radiation physics, and nuclear physics, this year’s Science Guide will teach you
about how mankind unlocked the power of the atom.
I, Jerry Zhao, former Decathlete of North Penn High School, will be your guide through this broad and
diverse field. I have always been fascinated by the physical sciences, humanity’s continual attempt to
explain the unexplainable and to understand the world around us. I hope that reading this guide will
inspire you to further your studies in the applied sciences.
This Power Guide will go above and beyond USAD in presenting information in a cleanly organized,
comprehensive, and easily searchable format. Since many concepts in this packet pertain to multiple
branches of science, I have done my best to present the big picture while remaining faithful to the
all-important details.
I have bolded key concepts, numbers, laws, names, dates, as well as any term bolded in the official
USAD Resource Guide. For your convenience, all bolded terms have been carefully tabulated and
organized in the Power Lists at the back of this guide.
Since USAD cannot possibly cover all concepts important to the field of nuclear science in the
Resource Guide, I have made it a point to identify and correct any gaps in information through the
addition of footnotes. While these footnotes are not testable material, they will add helpful contextual
information that will give you a better grasp of the subject material. Any contextual information I
include in a footnote will start with “Enrichment Fact:”
To ease the tediousness of this Power Guide, I have included my humorous comments and wry
remarks on the subject material in the footnotes as well. While you may be entertained by my feeble
attempts at comedy, you may choose to save yourself the pain by skipping any footnote which I have
signed with my name. I promise I won’t be offended.
I hope this Power Guide serves you well in your exploitation of nuclear science. The topics presented
here will help you in competition and beyond.
Happy studying!
Jerry Zhao
This year’s Science Resource Guide covers the history of atomic theory, quantum theory,
radioactivity, nuclear fission and fusion, and the development of the atomic bomb.
Section I covers 35% of the curriculum and 30% of the test material. This section walks you
through the history of classical atomic theory and discusses the phenomena that form the
foundation of modern quantum theory.
Section II covers 24% of the curriculum and 30% of the test material. This section discusses
the structure of atoms and the causes and effects of radiation.
Section III covers 20% of the curriculum and 25% of the test material. This section discusses
the science and applications of nuclear fusion and fission.
Section IV covers 21% of the curriculum and 15% of the test material. This section focuses
primarily on the Manhattan project and the development of the atomic bombs.



Classical Atomic Theory
 Foundations of atomic theory
 Atomic theory describes the atom, the universe’s basic building block
 The first atomic models were rooted in classical1 physics
 Today, quantum theory informs our current models
 Natural philosophers developed atomic theory in the 5th century BCE
 They believed matter to be composed of indivisible particles
 The earliest references to atoms came from Democritus and Leucippus
 Plato proposed four fundamental types of particles: fire, water, earth, and air2

He later added a fifth fundamental element, aether
 Each particle had a unique shape that represented its properties

Water flowed easily

It hence formed an almost-spherical isocahedron

Earth formed a cube since it was packed and solid
 The word “atom” comes from the Greek “atomos”, meaning “unable to be cut”
 These philosophers could not test any of their theories
 In the third century BCE, Aristotle proposed an opposing idea
 He described the basic elements as infinitely divisible
 Different ratios of the four elements resulted in different materials
th
 Aristotle’s anti-atomist views lasted into the 17 century
th
 In the 11 century, the study of atomism shifted from Europe to India
 The Middle Ages in Europe saw a decline in scientific thinking
 Islamic scholars combined Greek and Indian ideas in the Golden Age of Islam
 Their ideas formed the Asharite3 school of theology
 It returned to Europe in the Renaissance through Catholic priest Pierre Gassendi
 Gassendi reconciled atomism with the Catholic church
 He often discussed atomic theory with the philosopher Rene Descartes4
 Galileo Galilei also supported atomist views
 In the 17th century, Robert Boyle challenged atomic theory with corpuscular theory
1
2
3
4
Corpuscules5 are divisible particles which alter the properties of matter
 Isaac Newton promoted corpuscular theory in his 1704 book Opticks
 According to him, corpuscules made up all light
 In the 18th century, scientists first uncovered the principles of chemical reactions
 French chemist Antoine Lavoisier6 created the first list of elements
 He identified and named hydrogen and oxygen
 Lavoisier also discovered that mass is conserved in chemical reactions
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠 = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠
 French chemist Joseph Proust discovered that elements combine in fixed ratios
 In 1864, Dmitri Mendeleev created the periodic table of elements
 He arranged 64 known elements by their atomic weights
 Other atomic properties had not been discovered yet
 The periodic table predicted the existence of still-to-be-discovered gallium
 Modern theories of the atom
 English chemist John Dalton penned the first principles of atomic theory
 He borrowed ideas from Lavoisier and Proust
 In 1808, he published his ideas in A New System of Chemical Philosophy
 Dalton also tabulated atomic weights

Dalton’s Atomic Principles
•
•
•
•
•
Elements are composed of atoms
Atoms of the same element are completely identical
Atoms cannot be created, destroyed, or divided
Atoms react in simple ratios to form compounds
Atoms recombine in chemical reactions
 The development of the cathode ray tube allowed for many new observations
Michael Faraday observed that a voltage between a cathode and anode caused the
anode to glow
 The anode holds a positive charge, while the cathode holds a negative
 Negatively charged particles accelerate
between the cathode and anode
 These particles form a cathode ray7
 Televisions and computer monitors
display images using cathode rays8
 In 1897, J.J. Thomson measured the mass
of a cathode ray particle
 He found them to be 1800 times less
massive than hydrogen
 These negatively charged particles
are now called electrons
 Thomson also proposed that atoms
contained smaller particles like electrons in his plum pudding model

5
6
7
8

Electrons float around within the atom, like plums in plum pudding
 Hans Geiger and Ernest Marsden were Ernest Rutherford’s research partners
In 1911, Geiger and Marsden conducted the gold foil experiment
 They directed a beam of positive particles at a sheet of gold foil
 They expected the beam to pass straight through because the electrons in the gold
foil would be very small
 Instead, the gold foil deflected many of the particles in the ray at extreme angles
 Rutherford described the result as if “a 15-inch shell at a piece of tissue paper and
it came back and hit you”
 In response to this experiment, Rutherford designed a new model
 He placed a dense nucleus at the atom’s core
 Since the positively charged ray was sometimes
deflected backwards, the nucleus must be positively
charged
 He described the atom as a planetary system, with
electrons orbiting the nucleus
 Rutherford’s model had two inconsistencies
 Thermally excited atoms do not emit radiation at every
frequency
 According to classical physics, the electrons should
eventually fall into the nucleus

Early Quantum Theory
 Wave Theory of Light
 Many scientists also argued over whether light is a particle
or a wave
 Isaac Newton supported the corpuscular theory of light
 In his 1704 book Opticks, he described light as small
particles
 The corpuscular theory explained reflection, but not
refraction or diffraction
 The Dutch physicist Christiaan Huygens believed that light contained waves
 The wave theory explained how light diffracts around corners
 Optical experiments confirmed light’s wave-like properties
 In 1803, Thomas Young noted that two parallel slits cause alternating bands of light
and dark on a screen
 He called this phenomenon double slit diffraction
 It results from constructive and destructive interference from light waves

Sound waves produce a similar effect9
 In the late nineteenth century, James Clerk Maxwell theorized electromagnetism
 He described light as a wave of oscillating electric and magnetic fields
 Modern scientists now understand that visible light forms only a small portion of the
electromagnetic spectrum
 All electromagnetic waves travel at the speed of light
9
Different types of waves differ in their frequencies and wavelengths
 Frequency measures oscillations per second in Hertz (Hz)
 Wavelength measures the distance between oscillations

High frequency waves have low wavelengths
 Blackbody Radiation
 All matter releases energy in the form of thermal radiation
 The intensity of radiation is proportional to the temperature of the object
 At room temperature, thermal radiation remains invisible in the infrared band
 Around 1000 K, the thermal radiation
enters the visible band

For example, metals glow red-hot
 According to the classical explanation,
oscillating atoms act as “antennas” which
project radiation
 Blackbodies are theoretical objects which
absorb all incoming radiation
 Blackbodies remain in equilibrium by
constantly emitting thermal radiation
 The ultraviolet catastrophe refers to a gap
between
classical
expectations
and
10
experimental observations
 According to classical theory, the intensity of
thermal radiation should reach infinity as
wavelength decreases
 However, experimental results showed that
thermal radiation contains less wavelengths below ultraviolet than expected
 Energy Quantization
 Quantization refers to the discretization of possible energy levels
 Instead of existing at a continuous range of possible energies, a particle could only
exist at certain specific energy levels
 A quantum of energy describes the smallest energy level a particle could have
 All other energy levels are multiples of this fundamental quantum
 German scientist Max Planck first proposed energy quantization in 1900

Planck’s Formula
𝐸 = ℎ𝑓𝑛
𝐸 = Energy
ℎ = 6.63 × 10−34 𝐽 ⋅ 𝑠 = Planck’s constant
𝑓 = Frequency of oscillation 𝑛 = 1, 2, 3 … = the quantum number
Since the quantum of energy is tiny, quantization is difficult to detect
 The Photoelectric Effect
 Heinrich Hertz discovered in 1887 that shining ultraviolet light on a metal will cause it to
emit electrons
 This phenomenon is the photoelectric effect
 J.J. Thomson identified the emitted particles as electrons

10
Using classical theory, they reasoned that ultraviolet waves “charged” the electrons of
the atom with energy
 After enough energy transfer, the electrons would escape
 In 1900, Philippe Lenard observed contradictions to the classical theory

Classical Expectation Experimental Observation
Time delay during which the electron gains
Electron ejection happens instantaneously
energy before it is ejected
Any frequency of light should cause electron Only light above a certain frequency could
emission if the light intensity is high enough cause electron emission
Increasing light intensity increases the energy Increasing light intensity had no effect on
of ejected electrons electron energy
Light frequency has no effect on electron Increasing light frequency increased electron
energy energy
 Albert Einstein proposed the quantization of light energy in 1905
The massless photon is the smallest quantum of light
−19
 Photons have energy on the order of 10
𝐽
 Though
massless,
photons
possess
11
momentum
 In the photoelectric effect, photons collide with
electrons, ejecting them from the metal
 Einstein earned the 1921 Nobel Prize for this
insight
 In 1923, American physicist Arthur Compton noticed
that X-rays scatter upon impact with an electron
 This Compton scattering provided further proof
for light quantization
 Atomic Spectra
 Elements emit their own unique atomic spectra of light when excited
 A spectrum describes a set of frequencies of light
 Atomic spectra act as “fingerprints” that can be used to identify an element
 In the 1800s, atomic spectroscopy was developed

The technique identifies a sample’s chemical composition
 In 1868, scientists used atomic spectroscopy to identify helium in the sun

Helium was only discovered on Earth 30 years later
 An emission spectrum describes the set of frequencies emitted by an excited atom
 A spectroscope uses a prism to separate the emission into wavelengths
 Passing white light through a set of atoms creates an absorption spectrum
 Lines in the spectrum mark which frequencies were absorbed
 Generally, the absorption spectrum marks the gaps in the emission spectrum
 In 1885, Swiss physicist Johann Balmer found a relationship between the frequencies of
hydrogen’s emission spectrum
 Johannes Rydberg used Balmer’s findings in formulating the Rydberg formula

11
𝟏
𝟏
𝟏
= 𝑹𝑯 ( 𝟐 − 𝟐 )
𝝀
𝒎
𝒏
𝝀 = wavelength of emitted
light
𝑹𝑯 = 𝟏. 𝟎𝟗𝟕 × 𝟏𝟎𝟕 𝒎−𝟏 = the
Rydberg constant
𝒎, 𝒏 = positive integers
 The Bohr Model
 In 1913, Danish physicist Neils Bohr created an atomic model that accounted for energy
quantization
 He modified Rutherford’s solar system model
ℎ
 The electron’s angular momentum now had to be a multiple of
2𝜋
Bohr had no experimental justification for this change

Luckily, it worked anyway
 Bohr’s model has the following properties:
 Electrons move in circular orbits around the nucleus
 Only certain orbits, or energy levels, are stable
 Electrons do not radiate energy in their orbits
 This assumption contradicted known physical laws of physics12
 Electrons can move between energy levels
 Absorbing radiation increases the energy level
 Emitting radiation decreases the energy level

Electron Quantum Principles
Quantum
number, n
Electron’s potential energy levels
Ground state: n = 1, electron closest to nucleus
n > 1 → excited states
Ionization energy
Energy needed to remove an electron
Hydrogen: 13.6 eV
Electron’s
distance from
nucleus at each
level
𝒓𝒏 = 𝒏𝟐 𝒂𝟎
n = quantum number
𝑎0 = 0.0529 𝑛𝑚 = ground state electron radius
= the Bohr radius
Electron’s energy
at each energy
level
−(𝟏𝟑. 𝟔 𝒆𝑽)
𝑬𝒏 =
𝒏𝟐
eV, or electron volt, = energy of one electron
accelerated through a 1V potential difference
1 𝑒𝑉 = 1.6 × 10−19 𝐽
The negative sign implies that attraction keeps
the electron around the nucleus
 Bohr’s model explained why the Rydberg formula worked


12
𝑚 and 𝑛 correspond to the energy levels between which an electron transitions
Lines in the emission spectrum had corresponding quantum numbers
Series
Balmer
Discovered
Lyman
Paschen
1906-14
1908
State transition 𝑛 > 2 → 𝑛 = 2 𝑛 > 1 → 𝑛 = 1 𝑛 > 3 → 𝑛 = 3
 Bohr’s correspondence principle reconciled quantum and classical physics13
At high quantum numbers, quantum and classical predictions should match
 In the Bohr model, emissions at high quantum numbers match the electron’s orbital
frequency
 In 1914, James Franck and Gustav Hertz found evidence supporting the Bohr model
 They fired electrons through mercury gas in a heated tube
 The electrons lost energy in quantized amounts of factors of 4.9 eV
 Franck and Hertz found that mercury emits ultraviolet radiation with similarly
quantized amounts
 They won the 1925 Nobel Prize in Physics for this work
 The Bohr model still had several faults
 It could only describe the behavior of electrons in hydrogen
 The model did not explain why some lines in hydrogen’s atomic spectrum are actually
two very closely spaced lines
 It did not account for molecule formation

Particles as Waves
 The de Broglie Hypothesis
 French physicist Louis de Broglie first proposed the wave behavior of matter in his 1924
Ph.D. dissertation
 He compared the wave-particle behavior of light and the behavior of matter
de Broglie Hypothesis
𝜆=
𝒉 = Planck’s constant
ℎ
𝑝
𝑝 = particle momentum
𝜆 = de Broglie wavelength
It explained why electron angular momentum must be quantized
 If the electrons are instead waves, their wavelengths must be factors of their orbital
circumference
 In 1927, Bell Labs researchers confirmed the de Broglie hypothesis
 Clinton Davisson and Lester Germer observed a diffraction pattern when firing
electrons at nickel
 They wanted to quantify the roughness of the crystalline nickel
 Since only waves can diffract, the electrons must have wavelike behavior
 Many innovations rely on this finding

13
Transmission electron microscopes (TEMs) use the wave behavior of electrons to
achieve very high resolutions
 Light microscopes cannot resolve objects less than 500 nm, the approximate
wavelength of visible light
 A
TEM accelerates electrons with a
wavelength of 0.0037 nm to 100 keV
 We do not observe the wave behavior of matter
in everyday life
 Planck’s constant is very small
 An apple has a de Broglie wavelength a
trillion trillion times smaller than an atom
 Wave-Particle Duality
 Wave-particle duality refers to the wave-particle
behavior of both light and matter
 Electrons, photons, and neutrons all create a
diffraction pattern in Young’s double slit
experiment
 The experiment cannot detect the path of
any individual particle
 In 1926, Albert Einstein14 wrote to Max Born about the strangeness of quantum
mechanics
 He said that he could not believe God would play at dice

Modern Quantum Mechanics
 Quantum Mechanics
 Quantum mechanics emerged in 1925 to unify quantum theory
 Classical physics had a set of laws to describe wave and particle interactions
 Newton’s laws described particle interactions
 The differential wave equation described wave behavior
 In 1925, Austrian physicist Ernst Schrödinger designed an equation that describes the
wave-like behavior of particles
 The Schrödinger equation cannot be derived from existing theorems
 It has received experimental verification
 It’s solutions of wave functions are labeled by the Greek letter psi (𝜓 𝑜𝑟 Ψ)
2
 In 1926, Max Born suggested that Ψ = the probability distribution of a particle
 Two wave functions have particular importance
 A wave “packet” describes a particle freely travelling through space
 A “particle-in-a-box” describes a particle trapped in an infinite potential well
 Its energy levels depend on the mass of the particle and the size of the box
 The Schrödinger equation suggests particles can escape potential wells with quantum
tunneling
 Classical physics thought that a particle cannot cross potential barriers if its energy is
too low
 Particles actually have a non-zero probability of crossing potential barriers
14
 The scanning tunneling microscope (STM) uses quantum tunneling
The STM forms a potential barrier between the microscope and the sample
 It analyzes the current based on tunneling electrons with a resolution of 0.1 nm
 Quantum Probability

 In 1935, Schrödinger presented the Schrödinger’s cat scenario


It showed that a quantum system can exist in multiple states before being observed
A cat is placed inside a box with a container of poison
 The poison has a 50% chance of being released
 Until someone opens the box, the cat is said to be both dead and alive
Newtonian mechanics Quantum mechanics
The world is deterministic The world is probabilistic
Object positions are predictable and Repeated measurements of an object yield different
determined results
Works at larger scales Observed at the subatomic scale
 At large scales, uncertainty in measurements comes from the measuring instrument
 Quantum mechanics sets an upper limit on the precision of any measurement
Measuring an object alters the object
 Ex: shooting a photon at a particle alters the particle’s position and velocity
 German physicist Werner Heisenberg proposed the Heisenberg uncertainty principle
in 1927
 It states the impossibility of knowing a particle’s exact position and momentum
 Increasing the precision of one measurement decreases that of the other

𝒉
Heisenberg uncertainty principle: 𝚫𝒙𝚫𝒑 ≥ 𝟐𝝅
Δ𝑥 = uncertainty in position
Δ𝑝 = uncertainty in
momentum
ℎ = Planck’s constant
 Because the value of Planck’s constant is so small, the uncertainty principle only affects
microscopic measurements
 In 1940, George Gamow wrote the book Mr. Tompkins in Wonderland
 It describes a world with a very large Planck’s constant

A bank teller explored a “quantum jungle”

Elephants have fuzzy skin from uncertainty in their position

A gazelle spread out into a herd as if diffracted through a bamboo forest
 The Modern Quantum Model
 The modern model of the atom is the Schrödinger model
 Wave functions describe the electron’s waveform
 The amplitude of the wave function at a position describes the probability of
finding an electron at that position
 Electrons orbit the nucleus in a probability cloud
 The probability could does not need to be spherical
 Bohr radii represent their probable positions
 Three quantum numbers describe the electron’s position
 The principal quantum number, Bohr’s original number, is 𝑛
This number describes the energy of the electron
The orbital quantum number is ℓ where 0 ≤ ℓ ≤ 𝑛 − 1
 Electrons with the same ℓ and 𝑛 occupy the same subshell


Orbital quantum number
0
1
2
3
Subshell
s
p
d
f
Subshells can be described using their principle quantum number and letter

Ex: Subshell 3d has electrons with 𝑛 = 3, ℓ = 2

Superscripts denote electron configurations

Sodium’s electron configuration is 1𝑠 2 2𝑠 2 2𝑝6 3𝑠 2
 The orbital magnetic quantum number is 𝑚ℓ , −ℓ ≤ 𝑚ℓ ≤ ℓ
 The magnetic quantum number affects an atom’s behavior in a magnetic field

The Zeeman effect alters the energy of electrons with differing 𝑚ℓ values

Some spectral lines are actually two lines with slightly differing frequencies
 The spin quantum number 𝑚𝑠 does not come from the Schrödinger equation
 In 1925, scientists observed the yellow emission lines of sodium splitting
 This effect was called fine structure splitting
 In 1928, Paul Dirac derived a relativistic form of the Schrödinger equation
 It derives the spin quantum number from the electron’s angular momentum
 Electrons are a type of fermion, particles with half-integer spin
1
1
 Electrons can have 𝑚𝑠 = or −
2
2

Usually, the spin is characterized as “spin up” or “spin down”

Note that the spin number does not refer to the actual spinning motion

The electron would have to spin faster than the speed of light if so
The spin direction describes the electron’s contribution to the magnetic field
 The magnetic moment measures electrons’ tendency to align with the magnetic
field


Types of elements
Diamagnetic
•
Shells are filled with electrons; electron spins cancel to 0
•
Element is repelled by a magnetic field
•
Shells are partially filled; electron spins do not cancel out
Paramagnetic •
•
•
Ferromagnetic •
(iron, nickel) •
•
Atoms in the element align to a magnetic field
Atoms de-align when removed from the field
Shells are partially filled
Atoms in the element align, even without a magnetic field
Used in permanent magnets
Above the Curie temperature, magnetic properties are lost
 An electron’s state can be described by the four quantum numbers, 𝑛, ℓ, 𝑚ℓ , and 𝑚𝑠



Wolfgang Pauli proposed the Pauli exclusion principle
No two electrons in an atom have the same four quantum numbers
 No two fermions can occupy the same quantum state
Hence, electrons added to the atom fall to the lowest energy quantum level
 This property explains why noble gases like neon and helium do not react easily
They have filled electron shells15
 Alkali metals such as lithium and sodium, however, are extremely reactive

They have unpaired electrons
 The Pauli exclusion principle does not apply to bosons
 Bosons are particles with integer spin, not half-integer spin
 In 1924, Satyendra Bose and Albert Einstein suggested that cooling a gas of bosons
to 0 K would create a new state of matter
 This temperature is also known as absolute zero
 The “K” stands for “Kelvin”
 In 1995, Carl Weiman and Eric Cornell produced this new state of matter with laser
cooling
 They called it the Bose-Einstein condensate

Applications of Atomic Physics
 Lasers
 Atoms emit energy when an electron falls from a higher to lower energy level
 In spontaneous emission, the atom emits a photon in a random direction
 The atom remains excited for a few nanoseconds
 In stimulated emission, a passing photon can prompt a second photon release
 The passing photon’s oscillating electric field must have the same frequency as the
transition frequency of the excited electron
 The second emitted photon oscillates in synchrony with the first
 Laser stands for Light Amplification by Stimulated Emission of Radiation
 Lasers were first designed in 1960
 A reflective cavity contains and amplifies emitted light of uniform wavelength
 It creates a chain reaction of stimulated emissions
 A laser’s power ranges from 0.001 watts to 10,000 watts
 Lasers are widely used in medicine, industry, and research16
Qualities of Lasers Qualities of Ordinary Light and Radiation
Monochromatic: carry one light
Carry many different frequencies
frequency
Directional: do not spread as they
Decrease in intensity with distance squared
travel
Coherent: waves travel in the same
Do not travel in the same phase (ordinary
phase17, so they exhibit cleaner
light)
interference effects
 Materials used in the laser must meet two requirements


15
16
17
The element’s excited state must be metastable
 It has to remain excited state for some time before falling to the ground state
 Simulated emission can then occur before spontaneous emission
Most of the atoms in the laser need to be in the excited state
A process called population inversion creates a sample that contains more atoms
in the excited state
 A common design is the Helium-Neon (HeNe) laser
 HeNe lasers produce bright red 632.8 nm light
 HeNe lasers are used in physics18 demonstrations and barcode scanners
 Helium atoms excited by an electric current collide with neon atoms
 The neon atoms emit 632.8 nm radiation
 Laser cooling uses lasers to slow down the movement of atoms
 Room temperature gas particles move at 500 m/s
 Quantum effects cannot be easily observed at these speeds
 The scientific community awarded the 1997 Nobel Prize in Physics to the three
scientists who developed laser cooling
 Laser cooling relies on two principles
 (1) Conservation of momentum implies that each photon from the laser carries
some momentum to the gas particle it strikes

The laser exerts an overall pressure on the gas particle
 (2) The Doppler effect describes how moving towards or away from a wave source
alters the apparent frequency and wavelength

A siren moving towards you sounds high pitched, while a siren moving away
from you is low pitched
 The cooling laser has a frequency slightly below the transition’s
 Only particles moving towards the laser will be excited and slowed
 Systems involve six laser beams
 Two beams point in opposite directions along the x, y, and z axes
 In 2015, Stanford scientists cooled a sample of gas to 50 trillionths of a kelvin
 A rubidium atom at this temperature moves at 70 thousandths mm/se
 Atomic Clocks
 Atomic clocks use the timings of atomic transitions to tell time
 Unlike pendulum clocks, they do not respond to environmental changes
 Atomic transition timings will be identical for all atoms of an element
 In 1955, the first atomic clock was created using cesium
 This clock had an error of 1 second per 300 years
 Modern cesium clocks are accurate to 1 second per 300 million years19
 The accuracy of frequency measurements and ability to remove measurement
noise have improved
 In 1967, the second was redefined as the time that elapses during 9,192,631,770 hyperfine
transitions of cesium-137
 Hyperfine energy level differences result from magnetic interactions between
electron spin and nuclear spin in the ground state
 The second has become the most accurately defined SI unit of measurement
 Elements used in atomic clocks include hydrogen, rubidium, mercury, strontium, and
aluminum
 The National Institute of Standards and Technology uses cesium-13

18
19



Structure of the Nucleus
 Discovery of the Proton and Neutron
 Ernest Rutherford performed the gold foil
experiment in 1911
 He discovered the presence of a small, dense,
positively charged core at the center of the
atom
 In 1917, Rutherford carried out particle scattering
with nitrogen gas
 He was surprised to notice hydrogen nuclei
being produced from the collision
 He decided that the hydrogen nucleus
must be a fundamental building block of
matter
 Later scientists realized that the nucleus
contains just a single proton
 Surprisingly, the nucleus did not have a charge proportional to its mass
 He suggested that the nucleus contained neutral proton-electron pairs
 However, electrons cannot exist inside the nucleus
 According to the Heisenberg uncertainty principle, the electron has a minimum
energy in the nucleus

It exceeded experimentally observed electron energies
 Experimental observations of nuclear spin also contradict this idea
 In 1920, Rutherford that proton-electron pairs merge into neutrons
 In 1930, scientists found the neutron when bombarding beryllium with alpha particles
 The beryllium emitted neutral highly penetrating radiation
 This radiation did not behave like photons
 It had enough energy to eject photons from paraffin (wax)
 English scientist James Chadwick confirmed this particle was the neutron in 1932
 Nuclear Properties
 Nuclear physics studies the structure and interactions of the atomic nucleus
 Nuclei consist of protons and neutrons, known collectively as nucleons
−𝟏𝟗
 Protons have a positive charge of +𝟏. 𝟔 ⋅ 𝟏𝟎
Coulombs

Neutrons have a negative charge and a slightly higher mass than protons
 Nuclei are notated by their numbers of neutrons and protons
Nuclear notation: 𝑨𝒁𝑿
X Chemical symbol
Atomic number - number of protons
Z Unique to each element; can be omitted from notation e.g. uranium 238 = uranium with
atomic mass 238
N Number of neutrons
A
Atomic mass number, Z + N – total number of neutrons and protons
Always an integer
The relative mass number describes the average atomic mass of an element
 This number appears on periodic tables20
 It refers to the average atomic mass of all isotopes of an element, weighted by the
abundance of each isotope
 Atomic masses are measured in unified mass units, u
𝑀𝑒𝑉
2
 The 2 unit of mass comes from Einstein’s relation 𝐸 = 𝑚𝑐
𝑐

𝟏𝒖=
𝟏
𝟏𝟐
mass of
𝟏𝟐
𝑪 = 𝟏. 𝟔𝟔 × 𝟏𝟎−𝟐𝟕 𝒌𝒈 = 𝟗𝟑𝟏. 𝟒𝟗
𝑴𝒆𝑽
𝒄𝟐
Kilograms
Unified Mass Units (u)
𝑴𝒆𝑽
𝒄𝟐
Proton
1.672 × 10−27
1.007276 (~1 u)
938.28
Neutron
1.675 × 10−27
1.008665 (~1 u)
939.57
Weight in
Electron
9.109 × 10−31
1
5.486×10-4 (~1800
𝑢)
0.511
 The nucleus is about 100,000 times smaller than the atom
After the gold foil experiment, Rutherford measured the radius of the nucleus as
10−14 𝑚
 He conducted scattering experiments to find this result
−15 21
 The actual size of a nucleus is 10
𝑚 , a femtometer
 It takes its name from Italian Enrico Fermi
−10
 The electron cloud has a radius of 10
𝑚
 If an atom were a football stadium, the nucleus would be a marble22
 The equation 𝑟 ≈ 𝑟0 𝐴1/3 relates atomic radius to atomic weight
−15
 𝑟0 = 1.2 × 10
𝑚
 Nuclei have volume proportional to A
 Hence, all nuclei have the same density
 Isotopes
 Isotopes of an atom have equal numbers of protons but differing numbers of neutrons
 In Greek, “isotope” roughly means “the same place”

20
21
22
All isotopes of an element occupy the same spot on the periodic table
Isotopes have similar chemical properties
 Neutrons do not usually affect chemical bonding
They have very different nuclear properties, especially those of stability and abundance



Isotope of Hydrogen
Symbol
Abundance
Stability
Plain = hydrogen
1
1𝐻
99.99%
Stable
Deuterium
2
1𝐻
Very little
Stable
Tritium
3
1𝐻
Very little
Radioactive (unstable)
 Scientists create isotopes by bombarding nuclei with alpha particles, neutrons, or other
nuclei
 All isotopes heavier than Californium23 (z = 98) can only be created artificially
 Nuclear Forces
 The strong nuclear force2425 holds protons and neutrons together in the nucleus
 This force only acts over very short ranges
 The binding energy is the energy needed to split apart the nucleus
 The total mass of a nucleus’s components exceeds that of the nucleus26
 The extra mass comes from the binding energy
4
 2𝐻𝑒 has an unusually high binding energy, affecting its decay properties
Elements
4
2𝐻𝑒
=
2 × 10𝑛
+
2 × 11𝑝+
Mass
4.001506 𝑢
≠
2 × 1.008665 𝑢
+
2 × 1.007276 𝑢
Sum:
4.001506 𝑢
≠
Sum: 4.031882 u
Difference
0.03076 u
=
28.3 MeV, 7 MeV/nucleon
 A nucleus’s binding energy relates to its nuclear stability

Neutrons increase nuclear stability by not repelling protons
𝒁
Stability properties
≈56
High stability - highest binding energies, e.g. iron, nickel
>60
Binding energies decrease with atomic number
Larger nuclei have weak short-range nuclear forces

23
24
25
26
>20
Require many more neutrons than protons to remain stable
> 83
No number of neutrons can stabilize the nucleus
Quantum effects also contribute to nuclear stability
 Nuclei with even numbers of neutrons are more stable
 If the number of neutrons or the number of protons is a magic number, the nucleus
is unusually stable
The magic numbers are 2, 8, 20, 28, 50, 82, and 12627

Helium-4 and oxygen-16 are doubly magic
 In 1949, Maria Goeppert Mayer and Eugene Wigner designed a “shell” model
 This model of nucleons explained the presence of magic numbers
 The magic numbers equal the protons and neutrons needed to fill each shell
 Neutrons and protons are fermions and so follow the Pauli exclusion principle
 Protons and neutrons are fermions because they have half-integer spin
 When the number of protons or neutrons is even, the spins cancel out
 Particles of opposing spin align to decrease energy
 Nuclei with uneven numbers of protons or neutrons have a magnetic moment
 A nucleus with a magnetic moment will respond to an external magnetic field
 Aligning the magnetic moment with the field decreases the nucleus’s energy
 An oscillating magnetic field can cause the nucleus to rapidly oscillate between two
energy levels
 Magnetic resonance imaging (MRI)28 uses a strong magnet to align all of the
hydrogen-1 atoms in a body
 Radio waves target specific areas and break the alignment of hydrogen nuclei

Without the radio waves, the nuclei fall back and release energy

MRI does not damage cells, but still provides high resolution images

Radioactivity
 The discovery of radioactivity
 In 1895, German physicist Wilhelm Roentgen made the first observation of x-rays
 He experimented with a cathode ray tube
 The rays passed through cloth, paper, and books to cause a view-screen to glow
 He called them “X” rays since they were then unknown
 Roentgen won the 1901 Nobel Prize for this discovery
 French physicist Henri Becquerel discovered spontaneous radiation later that year
 He observed it in uranium salts that behaved similar to Roentgen’s x-rays
 Radioactivity refers to spontaneous radiation
 Radioactive isotopes spontaneously emit radiation and
 In the process, they transform into other isotopes
 Marie Curie measured the radioactivity of many substances
 She built on her husband Pierre Curie‘s work on crystals
 She analyzed pitchblende and torbernite
 These minerals that contain uranium
 Their radioactivity was proportional to the quantity of uranium
 Hence, a change in uranium’s atomic structure induced radiation
 In 1898, the Curies discovered polonium and then radium
 They named polonium after Marie’s home country Poland29
 The Curies and Becquerel jointly won the 1903 Nobel Prize in Physics
 Marie Curie also won the 1911 Nobel Prize in Chemistry
27
28
29
She is the only person ever to win two Nobel Prizes
Heavy exposure to radiation ruined Marie’s health
 She lost most of her sight in the 1930s and died in 1934 of aplastic anemia
 Her original notes are too radioactive to be handled without shielding30
 Radioactive decay
 In 1900, Ernest Rutherford and Frederick Soddy identified the three types of radiation:
alpha (α), beta (β), and gamma (γ)
 They also suggested that radiation results from radioactive decay
 During radioactive decay, unstable isotopes transform into stable isotopes
 Charge and nucleons are always conserved
 The parent nucleus X transforms into a daughter nucleus Y, except in gamma decay
 Gamma decay involves a descent from a higher energy state X* to a lower energy
state X*


Type
Emits
Alpha
Beta minus
Beta plus
Gamma
Helium nucleus
Electron and
antineutrino
Positron and
neutrino
Photon
𝟒
𝟐𝑯𝒆
𝟎 −
−𝟏𝒆
𝟎 +
𝟏𝒆
𝜸
Notation
Decay
formula
𝑨
𝒁𝑿
Example
238
92𝑈
→ 𝟒𝟐𝑯𝒆 + 𝑨−𝟒
𝒁−𝟐𝒀
→ 42𝐻𝑒 + 234
88𝑇ℎ
𝑨
𝒁𝑿
→
𝟏𝟒
𝟔𝑪
𝟎 −
−𝟏𝒆
̅
+ 𝒁+𝟏𝑨𝒀 + 𝟎𝟎𝒗
𝑨
𝒁𝑿
→ 𝟎𝟏𝒆+ + 𝒁−𝟏𝑨𝒀 + 𝟎𝟎𝒗
̅
→ 𝒆− + 𝟏𝟒𝟕𝑵 + 𝝂
𝑨 ∗
𝒁𝑿
𝟏𝟐 ∗
𝟔𝑪
→
→ 𝑨𝒁𝑿
𝟏𝟐
𝟔𝑪
+𝜸
 During alpha decay, an atom releases an alpha particle
An alpha particle is two protons and two neutrons
 It is the same as a helium nucleus
 This particle’s high binding energy
makes it energetically favorable for
decay
 Emitting 2 neutrons and 2 protons
individually is not energetically
favorable

Eg: 𝐴𝑍𝑋 → 10𝑛 + 10𝑛 + 11𝑝 + 11𝑝 + 𝐴−4
𝑍−2𝑌
 Alpha decay occurs in elements at least
as heavy as tellurium (𝑍 ≥ 52)
 Radioactive
nuclides release alpha
particles at 5% of the speed of light
 Alpha particles lose energy quickly due
to their high mass
 They usually stop in a few centimeters
 During beta decay, an atom releases either an electron or positron
 A positron is electron’s antiparticle – an electron with a positive charge
 Scientists only discovered beta plus decay decades after beta minus decay
−10
 The positron lasts for 10
seconds in a vacuum before annihilating with an
electron

30


Beta minus particles come from the nucleus, not the surrounding electron cloud
 A neutron in the nucleus transforms into a proton and an electron
1
1 +
0 −

0𝑛 → 1𝑝 + −1𝑒

Free neutrons outside the nucleus perform such decay in 15 minutes
In the 1920s, physicists including Neils Bohr realized that conservation of energy, spin,
and angular momentum did not occur in beta decay
 In 1930, Wolfgang Pauli hypothesized another particle in beta decay
 Enrico Fermi called this particle a neutrino, or “little neutral one”

The neutrino was first observed in 1950
Properties of the Neutrino
Neutrally charged
Fermion with half-integer spin
Essentially massless
Weakly interacts with matter
•
Released by nuclei in electron capture (K-capture):
The nucleus absorbs an electron from the K energy level of its electron cloud
•
Higher energy electron drops down to fill the shell, releasing an X-ray photon
•
•
A proton combines with the electron in the nucleus to produce a nucleus and a neutrino
The nucleus releases the neutrino
•
Example: 74𝐵𝑒 + 𝑒 − → 73𝐿𝑖 + 𝜈
 During gamma decay, an atom releases electromagnetic radiation, or photons


Gamma decay often proceeds after alpha or beta decay produces an excited nucleus
Photons produced by nuclear transitions differ from those in electron transitions
Nuclear transition photon Electron transition photon
Gamma rays
X-rays
Millions of eV
Tens of eV
 Scientists can create unstable isotopes that do not exist naturally


In 1934, Irene Joliot-Curie and Frederick Curie artificially synthesized a radioactive
isotope of phosphorous
 Irene was the daughter of Marie and Pierre Curie
They fired alpha particles at aluminum
4
2𝐻𝑒
+ 27
13𝐴𝑙 →
30
15𝑃
+ 10𝑛; 30
15𝑃 →
30
14𝑆𝑖
+ 𝑒+
Together they won the 1935 Nobel Prize in Chemistry
 Medically useful isotopes are produced artificially
 Over 3,000 radioactive isotopes have been synthesized
 The math of decay
 The timing of decay cannot be predicted for a specific nucleus31
 For a group of radioactive atoms, decay happens exponentially
 The number of decays is proportional to the number of nuclei present and to the time
that has elapsed
 The rate of decay has a similar exponential relation

31
Decay Laws
𝚫𝑵 = −𝝀𝑵𝚫𝒕
𝑵 = 𝑵𝟎 𝒆−𝝀𝒕
𝑹 = 𝑹𝟎 𝒆−𝝀𝒕
Δ𝑁 = number of decays in a period of time 𝑁 = number of nuclei present at a given time
𝑁0 = initial nucleus population
𝑅 = decay rate at a given time
t= time elapsed
Δ𝑡 = a period of time
𝑅0 = initial decay rate
𝜆 = decay constant
The decay rate is measured in Curies or Becquerels
10
 1 Ci (Curie) = 3.7 × 10 𝑑𝑒𝑐𝑎𝑦𝑠/𝑠
 1 Bq (Becquerel) 1 𝑑𝑒𝑐𝑎𝑦/𝑠

The Becquerel became the standard unit for decay rate in 1975
 The half-life of an isotope measures the time for half a sample of that isotope to decay

Examples:
Half-life equation
𝐥𝐧 𝟐 𝟎. 𝟔𝟗𝟑
𝑻𝑯 =
=
𝝀
𝝀
Hydrogen-4
10−22 seconds
Tellurium-12

1024 years
Isotopes with a long half-life have a more stable nucleus
 In any decay, a set of particles moves from a state with high potential energy to a state
with lower potential energy
 The mass of products will always be less than the mass of the original particles
 The potential energy difference comes from the mass difference
 Quantum mechanics explains why decay is probabilistic
 An alpha particle in a nucleus has a wave function
 The nuclear and Coulombic forces contain the alpha particle in a potential barrier
 The potential barrier has a size proportional to the nucleus’s size and charge
 Much like quantum tunneling, the alpha particle can escape the confining forces
 If the potential barrier is small, the alpha particle will escape more easily

This isotope would have a short half life
 Decay chains
 A decay chain occurs when the daughter nucleus is also radioactive
 Each decay step has its own half-life
 The three primary decay chains in nature occur in thorium, uranium, and actinium
 Neptunium’s decay chain does not occur in nature
 A chain starts with a heavy long-life isotope and ends with a stable isotope of lead
 In thorium-232’s chain, bismuth-212 performs either alpha or beta minus decay
 Decay chains explain why short-lived isotopes still exist in nature
 Radium-226 has a half-life of 1,600 years
 The Solar System has existed for 4.6 billion years
 All original radium-226 has decayed
 Uranium-238’s decay chain replenishes the isotope
9
 Uranium-238 has a half-life of 4.47 × 10 years
 Detecting Radioactivity
 Dosage measures the quantity of radiation an object receives
 The standard unit of dosage is the Sievert (Sv)
 One Sievert equals the effect of radiation that puts 1 Joule into 1 kg of tissue
 The United States uses the rem, equal to 0.01 Sieverts
 All methods of detecting radiation measure radiation’s ionizing effects
 Radiation ionizes atoms by removing electrons
Geiger counter
Scintillation counter
Invented by Hans Geiger32
Proportional counter
Provide information about the
energy level of the radiation
Measure energy of incoming
radiation
Essentially complex Geiger
counters
Radiation ionizes gas
atoms, releasing electrons
Radiation excites the crystal,
usually NaI
Incoming radiation trigger an
"avalanche" of ions
Electrons jump to wire and
trigger electric pulse
Excited crystal falls back to its
ground state and releases a
photon
Ions move towards a highvoltage wire, changing its
current
Electric pulse produces
clicking sound
Photomultiplier tube converts
photon to electric pulse
Change is proportional to
particle energy
Contain positively charged
wire surrounded by tube of
inert gas
Use scintillating material
instead of gas
 American Donald Glaser invented the bubble chamber in 1952


It and its counterpart, cloud chambers, track the path of radiation
The path provides information on the particle’s mass, charge, and momentum
 Positive and negative particles curve in opposite directions
Cloud chamber
Bubble chamber
Medium
Vaporized water or alcohol
Heated liquid hydrogen
Result
Particles are ionized. Pressure
condenses vapor around the
ions, forming trails
Pressure is decreased; particle
in an electric or magnetic field
leaves behind a trail of bubbles
Practical Applications of Radiation
 Sources of Radiation
 The average American receives 6.2 mSv of background radiation every year
 Half of this radiation comes from man-made sources, mostly x-ray procedures
 One x-ray delivers 0.02 mSv to the body
 Less than 0.1% comes from the nuclear industry
 The other half comes from natural sources33
32
33
Cosmic rays




Radon-222
High energy particles from
beyond the solar system
Mostly free protons
Shielded by the atmosphere
More prominent in high altitude
areas
>Ex: Denver receives 2x more
radiation than sea level
>Affects pilots' annual
permitted dosages 34
Other sources

Largest source of natural
background radiation

Radioactive
minerals

Found in decay chain of
uranium-238

Radioactive
nuclei in food

Accumulates in basements
as a dense gas


Second most frequent
cause of lung cancer after
smoking
Potassium-40 results in 0.4 mSv
per year

Can be tested for with
detection kits35
 Health Effects of Radiation36
 Ionizing radiation has enough energy to excite electrons
 Both ionizing and non-ionizing radiation can thermally excite atoms, causing burns
Non-ionizing radiation
𝐸𝑛𝑒𝑟𝑔𝑦 < 10 − 33 𝑒𝑉


Radio waves
Microwaves

Infrared, visible, sun light
Ionizing radiation
𝐸𝑛𝑒𝑟𝑔𝑦 > 10 − 33 𝑒𝑉



X-rays and gamma-rays
High energy UV light
Decay emissions
 Ionizing radiation damages living things when it strikes a molecule in the body
 An electron is removed, creating an ion or free radical3738 (neutral molecules with
unpaired electrons)
 The free radical react with other elements to produce irregular compounds
 Cells repair weak radiation damage only slowly
 However, the body cannot regenerate nerve cells
 Damage to DNA can lead to mutations, causing genetic disorders or cancer
 Overexposure to UV radiation causes sunburns, which can damage skin cells’ DNA
 Dead skin cells peel off
 Some forms of radiation are more dangerous than others
34
35
36
37
38
Gamma rays
Alpha particles
Most destructive form
Travel farthest into matter
Blocked by skin
Highly damaging if alpha emitter is consumed39
Interact weakly with matter
Neutrinos Do not affect human health
Strike earth from sun with flux of 1011 neutrinos / cm2
 Radiometric Dating
 Radiometric dating uses decay rates to calculate a material’s age
 The most common form is carbon dating
 In the 1940s, American Willard Libby developed carbon dating
 He won the1960 Nobel Prize in Chemistry
 Carbon-12 and carbon-13 are stable, but carbon-14 undergoes beta decay
 Carbon-14 transforms into nitrogen-14 with a half-life of 5,730 years
 Carbon dating only works with objects less than 50,000-years old
 Older materials have an undetectable carbon-14 concentration
Process of carbon dating
Cosmic rays produce free neutrons in the atmosphere
Free neutrons combine with nitrogen-14 to form carbon-14, which has a
natural abundance of 1 per trillion in living organisms and the atmosphere
Living organisms take in carbon dioxide in respiration
The organism dies, and carbon-14 in its body decays
Ratio of carbon-14 to carbon-12 decreases with time
Scientists measure the ratio to determine the organism’s age
 Fluctuations in the atmosphere’s carbon-14 concentration limit carbon dating’s accuracy
Varying intensities of the Earth’s and Sun’s magnetic fields alter the strength of
incoming cosmic rays
 Oceans hold carbon-14 as dissolved carbon dioxide
 Inconsistent ocean temperatures alter the rate at which carbon flows into the
atmosphere
 Uranium dating works on objects older than 50,000 years
 Uranium-238 is used instead of carbon-14
9
 This isotope has a half-life of 4.5 × 10 years
 The technique revealed that the oldest moon rocks and the oldest Earth rocks have
the same age
 The moon was probably formed out of the Earth in a primordial collision
 Uranium dating and argon-argon dating40 have recreated the fossil records

39
40
Geologists date the rock layers in which fossils are found
Primordial isotopes like uranium-238 were present in Earth’s crust at its formation
9
 Earth’s age is 4.5 × 10 years
7
 For a primordial isotope to be detectable its half-life must be > 5 × 10 years
 Industrial applications
 Radiation therapy destroys cancer cells’ DNA with ionizing radiation
 Without DNA, the cancer cells die
 The radiation must precisely kill only the cancerous cells
 Multiple low intensity beams intersect at the location of the cancerous cells41
 Gamma rays are most commonly used for cancer therapy
 Beta radiation is used to kill skin cancer and tumors close to the skin
 Radiation sterilization was first used in the mid-twentieth century
 Gamma rays are commonly used, generally using cobalt-60 as the emitter
 Eggs, grains, fruits, and vegetables can be sterilized without becoming radioactive
 It may chemically alter the food’s taste and nutrition
 The United States Food and Drug Administration regulates food irradiation
 Smoke detectors contain under 1 microgram of radioactive americium-241
 Americium-241 transforms into neptunium-237 in alpha decay
 The alpha particles produce a current in the detector
 Smoke absorbs the alpha particles, breaking the current
 Radioactive tracers use isotopes to create an observable path through a system


Uses of radioactive tracers
• Doctors42 prepare sodium iodide with radioactive iodine-131
instead of iodine-127
Medicine
• The patient ingests the harmless sodium iodide
• The radioactive iodide collects at the patient's thyroid glands,
providing a measure of thyroid health
• Doctors can then detect hemorrhage or tumor formation
Agriculture
• A radioactive solution is injected into a plant’s root system
• The solution’s uptake throughout the plant is measured
• Scientists can then detect information about the plant’s
fertilizer or other chemical use
• The engine's cylinder walls are coated with a tracer
Auto mechanics
• The engine is operated for some time
• The tracer's concentration in the lubricating oil is analyzed
41
42



Nuclear Reactions
 A brief history
 Two nuclei collide and form another nucleus
in a nuclear reaction
 Ernest Rutherford induced a nuclear reaction
when he discovered the proton in 1917
 He was scattering alpha particles from
nitrogen gas
4
14
 He induced the reaction: 2𝐻𝑒 + 7𝑁 →
17
1
8𝑂 + 1𝐻
 Unfortunately,
Rutherford did not
understand
the
nuclear
changes
43
occurring
 In 1932, Irish physicist Ernest Walton and British physicist John Cockcroft became known
as the first men to “split the atom”
1
7
4
 They performed the reaction 1𝑝 + 3𝐿𝑖 → 2 × 2𝐻𝑒
 Like chemical reactions, compounds react to form new compounds
 However, nuclear reactions release energy in the order of MeVs rather than eVs
Mass-energy conversion
Fusion
Fission
Direct
Involves light nuclei heavy nuclei particle-antiparticle pairs
% mass converted
0.7%
0.1%
100%
 Particle accelerators now collide particles with tremendous amounts of energy
The Large44 Hadron Collider accelerates protons to 99.9999% of the speed of light
 These protons have 1 TeV45 of energy
 The LHC is located at CERN, a research facility in Europe
 A reaction’s Q value measures its energy output or input

43
44
45
Reaction
Energy
Example
Mass of
reactants
Exothermic: Q > 0
Endothermic: Q < 0
Released as kinetic energy of products
and gamma rays
Requires input - kinetic energy of
reactants
2
1𝐻
+ 63𝐿𝑖 → 42𝐻𝑒 + 42𝐻𝑒
4
2𝐻𝑒
2.014101 𝑢 ( 21𝐻 ) + 6.015123 𝑢 ( 63𝐿𝑖 )
= 8.029224 𝑢
Mass of 4.002603 𝑢 ( 42𝐻𝑒) + 4.002603 𝑢 ( 42𝐻𝑒)
= 8.005206 𝑢
products
Net energy
+ 147𝑁 →
17
8𝑂
+ 11𝐻
4.002603 𝑢 ( 42𝐻𝑒) + 14.003704 𝑢 ( 147𝑁)
= 18.005677 𝑢
16.999132 𝑢 ( 178𝑂) + 1.007825 𝑢 ( 11𝐻 )
= 18.006957 𝑢
0.024018 𝑢 = 22.4 𝑀𝑒𝑉
−0.001280 𝑢 = −1.19 𝑀𝑒𝑉
Produces 22.4 MeV
Requires a little more than 1.19 MeV
 Actual energy input slightly exceeds the Q value in endothermic reactions


The Q value energy produces the product particles at rest
To maintain conservation of momentum, the products must have kinetic energy
𝒎
Required kinetic energy, 𝑲𝑬𝒎𝒊𝒏 = (𝟏 + 𝑴) |𝑸|
𝐾𝐸𝑚𝑖𝑛 = threshold energy
𝑀 = mass of stationary nucleus
𝑚 = mass of incoming nucleus 𝑄 = Q value of reaction
E.g.: reaction with 42𝐻𝑒 and
14
7𝑁
→ minimum energy = 1.53 MeV
 Fission reactions
 In nuclear fission, a massive nucleus releases energy and splits into fission products
 Most of the time, the heavy nucleus first collides with another particle
 In rare cases, nuclear fission occurs spontaneously
 Fission releases up to 100 MeV of energy per reaction
 Fission products, or fission fragments, are lighter nuclei released in nuclear fission
 These have a high neutron to proton ratio
 Neutrons stabilize protons in heavy nuclei
 “Neutron heavy” fission products decay further into even lighter nuclei46
Types of
nuclei
Fissile
Fertile
Neither
Performs fission after colliding
with a slow particle with
energy < 1 𝑀𝑒𝑉
Performs fission after colliding
with a fast particle with energy
> 1 𝑀𝑒𝑉
Never performs
fission
 English professor James Chadwick discovered the neutron in 1932
Earlier scientists created reactions by firing alpha particles or protons at nuclei
 After 1932, they used mostly neutrons instead
 The nucleus’s positive charge does not repel neutrons
 Low energy neutrons can still penetrate the nucleus
 This process is neutron bombardment
 In the 1930s, Enrico Fermi created new elements with neutron bombardment

46
Uranium
Neptunium
Plutonium
𝑍 = 92
𝑍 = 93
𝑍 = 94
Heaviest known element at the time;
target of neutron bombardment
New elements synthesized by
neutron bombardment
 In 1938, German physicists Otto Hahn and Fritz Strassman noticed that nuclei tend to





split in two after neutron bombardment
 The two pieces were each around half as massive as the target nucleus
 Ex: Barium is half as massive as uranium
 The existing theory behind decay did not explain this phenomenon
Lise Meitner and Otto Robert Frisch explained this observation using the liquid drop
model of the nucleus
 According to this model, heavy nuclei oscillate and split in half
 Otto Frisch first used the term “fission”
 He was alluding to how living cells split apart in biological fission
Neils Bohr realized that the energy released in nuclear fission could be harnessed
 He visited the United States and worked with John Wheeler and Enrico Fermi
In a chain reaction, a fission reaction sparks more reactions in neighboring nuclei
 Before the 1930s, scientists only knew of chemical chain reactions
 The finding proved a nuclear chain reaction to be theoretically possible
In 1933, Hungarian Leo Szilard envisioned the self-sustaining nuclear reaction
 The reaction had to be triggered by a neutron and release at least one neutron
The multiplication factor k measures the average number of released neutrons which
will trigger another fission
 Some neutrons are captured without fission, and others escape the system
Subcritical: 𝑲 < 𝟏
Critical: 𝑲 = 𝟏
Supercritical: 𝑲 > 𝟏
Number of reactions
decreases with time
Constant number of reactions →
constant power generated
Increasing number of
reactions over time
Cannot sustain decay
chains
Optimal for power generation
Optimal for nuclear
weapons
Calculating energy per reaction from binding energies of nucleons
Ex: 235 nucleons → 3.2 × 10−11 𝐽 = 200 𝑀𝑒𝑉 = 235 ∗ (8.5 𝑀𝑒𝑉 − 7.6 𝑀𝑒𝑉)
Binding energy of nucleons
Reactants: 7.6 𝑀𝑒𝑉
Products: 8.5 𝑀𝑒𝑉
Energy density
Gasoline: 4.4 × 104 𝐽
Uranium: 8.8 × 1010 𝐽
 The first nuclear chain reaction was observed in uranium-235



Uranium-235 can follow many decay paths
It is the only isotope useful for nuclear power generation
 Uranium-238 absorbs neutrons without performing fission
 It forms 95% of all uranium, while uranium-235 constitutes 0.7%
 Uranium-235 releases 2.5 neutrons per decay
Enriching uranium increases the concentration of useful uranium-235
Two possible Uranium-235 decay chains
𝟐𝟑𝟓
𝟏
𝟎𝒏 + 𝟗𝟐𝑼
𝟏
𝟎𝒏
→
+ 𝟐𝟑𝟓
𝟗𝟐𝑼 →
𝟏𝟒𝟏
𝟓𝟔𝑩𝒂
𝟏
+ 𝟗𝟐
𝟑𝟔𝑲𝒓 + 𝟑 𝟎𝒏
𝟏𝟒𝟎
𝟗𝟒
𝟓𝟒𝑿𝒆 + 𝟑𝟖𝑺𝒓 +
𝟐 𝟏𝟎𝒏
Most common; produces barium and krypton
Less common; produces xenon and strontium
Uranium enrichment
Power plants 3-4% uranium-235 → critical nuclear reactions
Weapons-grade 90% uranium-235 → supercritical nuclear reactions
Methods of uranium enrichment
•
Gas diffusion
•
(Early method)
•
•
Magnetic separation
•
(Early method)
•
•
•
(Modern method)
•
Gas centrifuge
Laser enrichment
(Experimental)
Uranium + fluorine →𝑈𝐹6 gas
Lighter uranium-235 has a higher velocity at uniform temperatures
Faster uranium-235 diffuses more quickly through a membrane
Uranium ions enter a magnetic field
The magnetic field bends the paths of the ions
Lighter ions follow a more curved path
Uranium hexafluoride gas is spun in a cylinder
Heaver ions flow to outer edge
Uranium-235 collects inside
•
•
A stream of ions passes in front of a laser
The laser accurately strikes lighter ions, shifting their paths47
•
Little energy is spent
 Fundamentals of fusion
 In nuclear fusion, two smaller nuclei collide and form a larger nucleus
Light nuclei conducting fusion
Heavy nuclei conducting fusion
Mass of reactants > mass of product
Mass of product > mass of reactants
Energy is released
Energy must be input
Example: Deuterium and tritium fuse into helium - 31𝐻 + 21𝐻 → 42𝐻𝑒 + 10𝑛
Mass of reactants:
Mass of products:
2.013553 𝑢 ( 21𝐻 ) + 3.015501 𝑢 ( 31𝐻)
= 5.029054 𝑢
4.001506 𝑢 ( 42𝐻𝑒) + 1.008665 𝑢 ( 10𝑛)
= 5.010171 𝑢
Mass of products – mass of reactants = −0.018883 𝑢 = −17.59 𝑀𝑒𝑉
 Electric forces between nuclei create a barrier to fusion called the Coulomb barrier
Two nuclei brought very close together have an attractive nuclear force that overcomes
the Coulomb barrier
 Quantum tunneling explains nuclei’s ability to cross the Coulomb barrier
7
 Colliding nuclei have temperatures near 10 K
 In thermonuclear fusion, nuclei collide and form tightly bound nuclei

47
Like chemical combustion, it requires high temperatures to initiate
 Continuous energy releases sustain both types of reaction
 Products have less mass, and energy is output
 Stellar fusion produces energy in stars
 Their cores are fusion reactors operating at millions of degrees
 Young stars perform hydrogen fusion, while old stars perform helium fusion

1920
English physicist Arthur Eddington proposed that stars produce
energy by combining hydrogen into helium
1934
Australian Mark Oliphant and Ernest Rutherford collide two
deuterium nuclei to form helium
1939
Hans Bethe describes the proton-proton chain and the carbonnitrogen-oxygen cycle
1967 Hans Bethe wins the Nobel Prize for describing stellar fusion
 The Sun converts 657 million tons of hydrogen into 653 million tons of helium per day
The Sun is 74% hydrogen and 25% helium by mass
4 tons of energy is released as radiation, light, and the solar wind48
 The solar wind is a stream of light particles ejected during fusion
 A star’s gravity provides the energy for thermonuclear fusion
 Fusion energy generates pressure outwards
 Stars need to be hot and dense enough for fusion reactions to occur
 Light stars conduct a fusion process called the proton-proton chain


The Proton-Proton Chain
Reaction
Energy Output
2 × ( 11𝐻 + 11𝐻 → 21𝐻 + 𝑒 + + 𝑣)
𝑄 = 2 × (0.42 𝑀𝑒𝑉)
2 × ( 11𝐻 + 21𝐻 → 32𝐻𝑒 + 𝛾)
𝑄 = 2 × (5.49 𝑀𝑒𝑉)
3
2𝐻𝑒
Total
+ 32𝐻𝑒 → 42𝐻𝑒 + 11𝐻 + 11𝐻
𝑄 = 12.86 𝑀𝑒𝑉
4 11𝐻 → 42𝐻𝑒 + 2𝑣 + 2𝛾 + 2𝑒 +
𝑄 = 24.68 𝑀𝑒𝑉
Positrons release more energy after colliding with electrons
2 × (𝑒 + + 𝑒 − → 𝑄); 𝑄 = 2 × (0.511 𝑀𝑒𝑉) = 1.02 𝑀𝑒𝑉
The slowest first step acts as a bottleneck
 It regulated the conversion rate
 Heavier stars follow a different process, the carbon cycle (CNO cycle)
 The CNO cycle converts hydrogen to helium, with no net carbon change
 CNO stands for carbon-nitrogen-oxygen, the intermediate elements

Applications
 Nuclear reactors
 Nuclear reactors harvest energy from sustained chain reactions
48
Reactors must control the reaction rate
One kilogram of uranium-235 provides
the same energy as 20,000 tons of TNT
 In a reactor, the moderator slows down
emitted neutrons
 The neutrons emitted by reactions
have very high kinetic energies around
2 MeV
 Uranium-235
does not easily
absorb fast neutrons
 Slow neutrons conduct fission with
uranium-235
 Uranium-238 does not absorb slow
neutrons
 A good moderator absorbs much of the neutron’s energy
 The moderator should have nearly the same mass as the neutron
 Moderators with different masses absorb little energy

Imagine a ping pong ball bouncing off a billiard ball49


Moderators
Hydrogen, 𝟏𝑯


Deuterium, 𝟐𝑯
Theoretically is the best moderator
but in practice absorbs neutrons to
form deuterium
Does not slow neutrons effectively


Graphite, 𝟏𝟐𝑪
Slows neutrons without

absorbing them
Is found in heavy water, 
replacing hydrogen-1
Is used in first
nuclear reactor
Slows neutrons after
100 collisions
Control rods50
Maintain reactor’s criticality; contain neutron-absorbing boron
Reactor startup, K > 1
Reactor operation, K =1
Reactor shutdown, K <1
Rods retracted
Rods control reaction rate
Rods inserted
 Enrico Fermi created the first nuclear reactor on December 2nd, 1942
He constructed it on the University of Chicago’s racquet courts51
 A pile of graphite bricks surrounded the uranium fuel
 Cadmium control rods penetrated the reactor core52
 A concrete containment chamber surrounds the steel reactor vessel
 The vessel contains the core, which holds fuel surrounded by a moderator
 Modern reactors use water for the moderator
 The fuel usually contains 2-4% uranium-235 and 96-98% uranium-238
 Most reactors are a type of light water reactor

49
50
51
52
Light water reactors
Heavy water reactors
Boiling water
Pressurized water
Loop of water both
cools reactor and
powers steam turbine
Pressurized cooling loop transfers
energy to a secondary loop which
generates steam
Heavy water moderates
neutrons extremely well
Radioactive coolant does not enter
steam turbine
Can induce reactions in
unenriched fuel
Common in United States
Common in Canadian reactors
More expensive
Employs relatively
simple design
 Coolant flows through the core and absorbs thermal energy
Most reactors use water
 A few use liquid sodium
 Coolant exiting the reactor boils water to produce steam
 The steam generates electricity by powering a conventional steam turbine
 Nuclear reactors have many applications
 They can generate electricity, including to power ships and submarines
 They also generate neutrons for research, medical, and industrial use
 Nuclear reactors generate a significant portion of the world’s energy needs

1951 EBR-153 reactor in Arco, Idaho generates electricity for four light bulbs
1954 Soviet Union connects a nuclear reactor to the power grid
2012 Nuclear power generates 10.9% of the world’s energy
2015 438 reactors operate in 30 countries
 Breeder reactors
 Plutonium-239 is useful for nuclear fuels and nuclear weapons
 Plutonium-239 is not a fission product, but rather forms from uranium-238
Origins of Plutonium-239
Uranium-238 absorbs a neutron without reacting
Uranium 239 has a half-life of 23.5 minutes before
decaying into neptunium-239
Neptunium-239 performs a second beta decay
238
𝑈 + 1𝑛 →
239
𝑈→
239
0
−1𝛽
𝑁𝑝 →

53
In World War II, they produced plutonium for nuclear weapons
𝑈
+ 239𝑁𝑝
0
−1𝛽
 Breeder reactors generate plutonium-239
239
+ 239𝑃𝑢
Less effective moderators increase the number of neutrons in the reactor
 Liquid sodium leaves neutrons with high kinetic energy
 These neutrons react with uranium-238 to form plutonium-239
 Some breeder reactors generate more fuel than they consume
 Breeder reactors have decreased since the 1980s and halted in the United States
 There is nothing wrong with the uranium fuel supply
 It has not been substantially depleted
 However, breeder reactors produce the fuel for nuclear weapons
 Governments fear the proliferation of weapons-grade nuclear fuel
 In addition, breeders are expensive and complex
 Nuclear power challenges
 Nuclear reactors produce hazardous radioactive wastes54
 Some wastes have very long half-lives and stay hazardous for a long time
 Plutonium-239 has a half-life of 24,000 years
 These wastes must be contained safely as long as they remain dangerous
 Some fission products decay away quickly and can be stored temporarily
 Nuclear reactors must be decommissioned after 30 years of operation
 Radioactivity builds up on the reactors components
 Structural materials degrade after prolonged exposure to ionizing radiation
 Old reactors must be completely dismantled and radioactive materials removed
 This process is very expensive
 Nuclear reactors still hold many advantages over coal, oil, and natural gas plants55
 Coal power plants release many greenhouse gases and expose workers to radon
 Nuclear power plants only release water vapor, which converts to snow and rain
 Nuclear plants release very little radiation, an average of 0.1 mSv per year
 This amount equals 0.003% of the average annual background radiation
1
 It also constitutes
the radiation from one chest x-ray
200

 The United States produced 1/3 of the world’s nuclear energy in 2013
Nuclear power provided 19.5% of the country’s energy in 2014
 In contrast, France generates 75% of its electricity through nuclear plants
 No new plants have been developed in the United States since the 1970s
 Political and economic forces have halted the building of new power plants
 Although the risk from nuclear power plants is small, accidents are high-profile and
alarming
 Nuclear power plants are very expensive to build
 The United States still builds new reactors to add to existing plants
 Accidents can be meltdowns or explosions
 In meltdowns, the nuclear fuel overheats and melts through its containment
 Explosions occur due to over-pressurized coolant
 The Three Mile Island5657 incident occurred on March 29, 1979 in Pennsylvania

54
55
56
57
Three Mile Island Accident
Water pump shuts down
Secondary coolant loop stops circulating
Reactor shuts down but still generates heat
Secondary loop boils off, leaving only primary loop
Primary loop overheats and overpressurizes
Water floods the containment structure and is pumped outside
Though it was the worst accident in United States history, it had no impact on public
health
 The Chernobyl incident occurred on April 26th, 1986 in the former Soviet Union
 This was the worst nuclear accident in history
 A sudden power surge ruptured the reactor vessel, causing a large explosion
 Its radioactive cloud had 400 times more radiation than the Hiroshima bomb
 Thirty people died and hundreds of thousands had to evacuate58
 Such a disaster could not occur in the United States, as it uses different plant designs
 On March 11th, 2011, the Fukushima Daiichi nuclear accident occurred in Japan
 It stands as the worst accident since Chernobyl

Fukushima Daiichi Nuclear Accident
9.0 earthquake forces reactor to shut down
Control rods drop down into the core
Cooling reactors need supply of coolant
Tsunami cuts power to the primary and secondary coolant pumps
Reactors melt down and explode
500,000 residents evacuated
A 2013 report finds that evacuated civilians suffered no health effects
All 54 Japanese nuclear plants shut down
 Generation IV reactors will be constructed from 2030

These reactors minimize waste, increase safety, and impede nuclear proliferation
 Nuclear weapons
 Weapons research drove nuclear science in the 1940s
 Nuclear weapons release nuclear energy rapidly in supercritical (K >1) reactions
 They release energy on the order of 1 to 500,000 tons of TNT
 The critical mass refers to the minimum mass of fissile fuel in a nuclear weapon59
 In uranium-235, the critical mass forms a 6.8 cm diameter sphere
 The Nagasaki bomb used another common fuel, plutonium-239
58
59
Below the critical mass
At the critical mass
Above the critical mass
Neutrons escape fuel before
colliding with a nucleus
Every fission causes one more
fission
The reaction rate increases
exponentially
Nuclear fuel remains below critical mass until detonation
 At detonation, conventional explosives bring the pieces together
 Early weapons used a gun-type design
 An explosive fires half of the mass at the other down a barrel
 Modern implosion-type weapons use a sphere of explosives to compress the fuel
 Applications of fusion
 Thermonuclear weapons and hydrogen bombs release energy in nuclear fusion
 The fusion bomb originated in the Manhattan Project
 Hungarian Edward Teller suggested a fission bomb could trigger a fusion bomb
 In 1951, Teller and Stanislaw Ulam designed a fusion bomb
 Teller became known as the “father of the hydrogen bomb”
 The first fusion bomb detonated in 1952, using Teller’s multistage design
 Fission charges compress fission and fusion fuel, detonating the primary bomb
 The primary stage compresses and detonates a secondary fusion bomb
 It released 10.4 megatons of energy, 450 times more than the Nagasaki bomb
 The largest hydrogen bomb ever built was the Tsar Bomba
th
 The Soviet Union tested this weapon on October 30 , 1961
 It had the same energy as 50 million tons of TNT60
 Scientists have been trying to harness power from fusion reactions for 50 years
 Potential fusion reactions for power generation must satisfy certain criteria

Criteria
Components
(1) Must be exothermic
(2) Must conserve proton and
neutron number

(1) Light nuclei with minimal Coulombic repulsions
(2) Two reactants to maximize collision probability
(3) At least two products to conserve momentum
Fusion reactions with deuterium and tritium are candidates for power generation
 However, hydrogen is optimal for use in nuclear fusion
 It is the most plentiful element and all isotopes appear in water
Potential fusion reactions
Reaction
Energy output
2
1𝐻
+ 21𝐻 → 32𝐻𝑒 + 10𝑛
2
1𝐻
𝑄 = 3.27 𝑀𝑒𝑉
+ 21𝐻 → 31𝐻 + 11𝐻 61 
𝑄 = 4.03 𝑀𝑒𝑉
1 gram in every 30 liters of sea water,
Deuterium provides same energy as 10,000 liters
of gasoline
Tritium
60
61
Low natural abundance; half-life of
10 years
2
1𝐻
+ 21𝐻 → 42𝐻𝑒 + 10𝑛
𝑄 = 17.59 𝑀𝑒𝑉
World’s deuterium supply contains
more energy than its fossil fuel plus
uranium supplies
Synthesized by breeding lithium-6
6
1
3
4
3𝐿𝑖 + 0𝑛 → 1𝐻 + 2𝐻𝑒
 Fusion reactors have many advantages over fission reactors
Fusion reactors cannot melt down as the reaction cannot become supercritical
 Reaction products are not used in subsequent reactions
 Fusion produces no pollution or radioactive waste, only helium
 Fusion energy requires extremely high temperatures
 In the sun, fusion occurs at over 10 million K
 These extremely high temperatures are the greatest barrier to fusion energy62
 Fusion reactors must be self-sustaining at ignition, like fission reactors
 The energy released by a reaction can power subsequent reactions
 Scientists have not yet been able to achieve ignition
 Reactors must compress nuclei to extremely high densities to increase reactions
 Electrons separate from nuclei in atoms above their ionization energies
 The cloud of positive nuclei and negative electrons forms a plasma
 Most structural components would vaporize at these temperatures and densities

Lawson’s Criteria
Deuterium-tritium fusion
𝑛𝜏 ≥
1014 𝑠
𝑐𝑚3
𝑛 = plasma ion density
Deuterium-deuterium fusion
𝑛𝜏 ≥
1016 𝑠
𝑐𝑚3
𝜏 = plasma confinement time
 In 1957, J.D. Lawson devised conditions for fusion power generation
 Two methods exist for generating and sustaining fusion
 In magnetic confinement, electromagnets trap high-temperature plasmas
A strong magnetic field bends the paths of ions in the plasma cloud
 Magnetic confinement systems trap moving ions in a “magnetic bottle”
 Tokamaks are toroidal containment devices with two magnetic fields
 They trap the plasma in a ring shape
 The Soviet Union developed the tokamak after World War II
 Magnetic confinement aims to sustain nuclei at high temperatures
 Inertial confinement fusion (ICF) systems use laser beams to compress atoms
 A laser array compresses a target pellet containing deuterium and tritium
 The pellet ionizes into a plasma
−9
 Less than 10
seconds later, the particle reaches 108 K and fusion occurs
 ICF systems prevent nuclei from drifting apart by forcing them together quickly
 The National Ignition Facility63 is the world’s largest ICF device
 It lies in Lawrence Livermore National Laboratory in Livermore, California
 The NIF targets a 2mm hydrogen pellet with the world’s most powerful laser
 In 2012, the NIF shot a 500 trillion watt laser pulse
 This pulse has 1,000 times more energy than the United States uses in an instant
 At break-even, the energy output exceeds the energy needed to trigger fusion
 Princeton’s Tokamak Fusion Test Reactor tried to achieve this point but failed
 It heated plasma to over 200 million K, above hydrogen’s ignition temperature

62
63
The TFTR operated from 1982 and shut down in 1997 after 15 years
The Joint European Torus (JET) is another tokamak design that operates today
The world’s largest experimental fusion system is the ITER in France
 ITER originally stood for International Thermonuclear Experimental Reactor
 The European Union, India, Japan, Korea, China, Russia, and the United States
collaborated on this project
 ITER uses a magnetic confinement system, hoping to prove its feasibility
 It will finish construction in 2027 and run deuterium-tritium fusion experiments






The Manhattan Project
 Background
 In the decades after World War I, Italy and Germany fell under fascist rule
 Italy’s Benito Mussolini and the Nazi Party’s Adolf Hitler led their respective countries
 The two allied countries carried out racial discrimination and genocidal policies
 Germany’s invasion of Poland in September 1939 started World War II
 Enrico Fermi and Leo Szilard fled to the United States in 1939
 Leo Szilard had first conceived of the nuclear chain reaction in 1933
 He warned Franklin Delano Roosevelt that Germany might be researching nuclear
weapons
 He proposed that the United States follow suit and also stockpile uranium
 Szilard signed the letter with Einstein’s name to attract more attention
 Einstein, a German-born Jew, also worried about Nazi Germany
 When Hitler became chancellor in 1933, Einstein chose to stay in the United States
 Einstein was a pacifist and opposed creating nuclear weapons
 He shared Szilard’s concern about German research into nuclear weapons
 In response to Szilard’s letter, Roosevelt created the Advisory Committee on Uranium
 National Bureau of Standards director Lyman Briggs chaired the committee
 It had the task of recommending how to proceed with nuclear research
 On November 1, 1939, it reported that the United States should support Fermi and
Szilard’s research in chain reactions
 The United States purchased $6,000 of uranium oxide and graphite64
 At the time, Fermi believed that nuclear reactors were possible, but not bombs
 Pilot research
 Vannevar Bush pushed for research on nuclear weapons
 Bush was a science administrator and president of the Carnegie Foundation
 He could influence United States policy in his position
 By 1940, he was concerned about German expansion
 He noticed a lack of cooperation between researchers and the military
 In June 1940, Bush became the chair of the National Defense Research Committee
64
Roosevelt approved this committee in less than 15 minutes
This committee oversaw research and development of nuclear weapons
 The S-1 subcommittee studied uranium enrichment
 It included Ernest O. Lawrence, director of the Radiation Laboratory65 at the
University of California, Berkeley
 He had invented the cyclotron, a particle accelerator and mass spectrometer

As a mass spectrometer, it could separate uranium-235 from uranium-238
 The S-1 committee needed to produce a critical mass of uranium-235
 Nobody knew if the critical mass was small enough to fit on a bomber
 The committee explored gaseous diffusion, centrifuge separation, and
electromagnetic separation as enrichment methods
 Simultaneously, Great Britain developed its own nuclear weapons program
 They estimated the critical mass to be on the order of 10 kg
 Its representative, physicist Mark Oliphant, visited the United States in August 1941
to help and assess the American program
 He encouraged the American researchers by sharing British research with them
 By 1941, the atomic bomb seemed to be possible
th
 Roosevelt and his Vice President Henry Wallace met on October 9 , 1941 with
Vannevar Bush
 Bush summarized the progress of American and British research
 Roosevelt asked Bush to estimate the cost of an atom bomb

President Roosevelt wanted the US Army to manage bomb construction
th
 Japan attacked Pearl Harbor on December 7 , 1941
 The United States declared war on Japan the next day
 Starting production
 In March 1942, Bush informed Roosevelt that
Lawrence’s cyclotron had successfully refined uranium
“I think the whole thing
 He believed that a bomb would be complete by
should be pushed not only in
1944
regard to development, but
 Roosevelt shared his concerns in a response (right)
also with due regard to time.
 In May 1942, Arthur Compton asked J Robert
This is very much of the
Oppenheimer to perform calculations for the chain
essence.” - FDR
reaction
 Oppenheimer worked at the University of California,
Berkeley66
 He formed a team with Hans Bethe, John Van Vleck, Edward Teller, Felix Bloch,
Emilio Segre, and Robert Serber
 They found they needed double the amount of fission fuel previously estimated
 However, they confirmed that a fission weapon could be built
 In June 1942, the S-1 committee researched fuel enrichment

Vannevar Bush allocated $85 million for constructing enrichment plants
 Three plants were built to enrich uranium, and one more for plutonium
 The United States stockpiled uranium on Staten Island
 It stored 12,000 tons of uranium ore from Colorado and Canada


65
66
 Fermi created a chain reaction at the University of Chicago on December 2, 1942
The S-1 committee then finalized plans for bomb development
 Roosevelt agreed to the proposals and allocated $500 million for the project
 The Manhattan Project
 The Army Corps of Engineers managed bomb production
 On August 13, 1942, they set up an office in Manhattan, New York
 The office became the Manhattan Engineer District, or The Manhattan Project
 General Leslie R. Groves became the project’s director in September 1942
 He came from the Army Corps of Engineers, where he had worked on the Pentagon
 Groves drew criticism for his abrasive and critical personality
 His focused, goal-oriented management helped the project meet crucial deadlines
 Groves selected Oppenheimer as the leader of Project Y on July 20th, 1943
 Project Y referred to the Manhattan Project’s weapons development lab
 Ernest Lawrence and Arthur Compton were too busy to serve as director
 Compton suggested Oppenheimer
 Oppenheimer’s mastery of science and engineering concepts impressed Groves
 Others opposed this choice
 Oppenheimer had not won a Nobel Prize and lacked administrative experience
 His wife Kitty and brother Frank had communist sympathies
 The Manhattan Project’s primary enrichment plant lay at Oak Ridge, Tennessee
 In October 1942, the Army Corps of Engineers purchased 60,000 acres of land
 It named the land Clinton Engineer Works in January 1943
 Oak Ridge was a city founded to house the tens of thousands of new employees
 It was Tennessee’s fifth largest city in 1945
 The Oak Ridge plant contained many small facilities
 Construction of the world’s second nuclear reactor started on February 2, 1943
 The X-10 Graphite Reactor first operated on November 4, 1943
 The Y-12 electromagnetic separation plant separated uranium isotopes
 This enrichment method based on the cyclotrons was inefficient but low-risk
 The K-25 gaseous diffusion plant performed enrichment with gaseous diffusion
 It was one of the largest single-roofed buildings in the world
 At the time, gaseous diffusion had not been demonstrated to work
 It required a barrier that could separate isotopes by their average speeds
 The enrichment level of this plant steadily increased as the years went by
 The S-1 committee rejected the centrifuge method, so no such plants were constructed
 Tests at the X-10 reactor showed that a full-scale reactor was needed to produce
plutonium
 Groves hired the DuPont chemical company to construct the plant
 DuPont had worked on various war contracts and operated reactors
 Since Oak Ridge was close to Knoxville, DuPont decided to construct the plant on the
Columbia River in Washington state
 Knoxville was a populated city
 Groundbreaking at the Hanford Engineer Works occurred in March 1943
 The B-Reactor at Hanford was the world’s first large plutonium generator
 Construction started in October 1943
 In September 1944, criticality was achieved

 Los Alamos
 In 1942, scientists worked on the Manhattan Project from across the country
 The project’s administration decided to form a centralized laboratory
 Oppenheimer wanted the laboratory to be in a remote location
 General Groves founded Site Y in northern New
Mexico in 1943
 It lay near the Los Alamos Ranch School, 30
miles northwest of Santa Fe
 The secret location had a mailing address at a
P.O. box in Santa Fe
 Today, Site-Y is known as Los Alamos
National Laboratory
 In 1943, Oppenheimer recruited scientists from
across the nation to join Los Alamos
 His hires included “Berkeley Luminaries” Hans
Bethe and Edward Teller
 Many of the scientists had won Nobel Prizes
 Richard Feynman and Emilio Segre
would win Nobel Prizes later
 Albert Einstein never joined the Manhattan
Project
 He had to create a detonation mechanism that
could rapidly reach supercritical mass
 Subcritical masses might produce smaller explosions and blow apart the material
 In this case, the bomb pre-detonates, or “fizzles”
 Two types of detonation mechanisms were proposed
 At first, engineers designed a gun-type plutonium bomb
 They dubbed it the “Thin Man” due to its unusual shape
 The first shipment of plutonium arrived at Los Alamos in April 1944 from X-10
 Emilio Segre realized that reactor-bred plutonium had more impurities than cyclotronmade plutonium
 It contained too much plutonium-240, which tends to start the chain reaction too
early and fizzle out
 Mathematician John von Neumann proposed an implosion-type weapon in
September 1943
 He relied on earlier work by physicist Seth Neddermeyer
 Although more complex, it brought the fuel together more quickly
 In 1944, Oppenheimer instructed researchers to abandon the gun method
 On August 7th, 1944, General Groves announced that an implosion bomb would be
completed by spring 1945
 A uranium gun-type bomb would be finished later in August 1945
 The team planned a full-scale test outside Alamogordo, New Mexico
 Groves only approved the test after assuring that the nuclear material would be
recovered if the bomb fizzled
Oppenheimer named the test “Trinity” after a
poem by John Donne67
“We knew the world would not
 The bomb, nicknamed the “gadget”, used
be the same. A few people
Hanford B plutonium
laughed, a few people cried,
 A 100-foot-tall tower suspended the bomb to
most people were silent.”
produce maximum power
– Oppenheimer, on reactions to
 Energy from a midair detonation would
the Trinity test
expand in a sphere
 Observers sat in bunkers 10,000 yards north,
west, and south of the tower
 The Trinity test occurred at 5:30 am on July 16th, 1945
 The bomb released the same energy as 20,000 tons of TNT
 A mushroom cloud rose 7.5 miles into the air
 The bomb left a crater 5 feet deep and 30 feet across
 The steel tower was completely destroyed68

Nuclear Weapons and International Security
 Atomic bombing of Japan
 Roosevelt unexpectedly died in office on April 12, 1945
 Harry Truman replaced him just three months after becoming Vice President
 He did not know of the Manhattan Project
 General Groves and Secretary of War Henry Stimson discussed the deployment of the
bomb with Truman on April 25
 By this time, the Allies had the upper hand in the war against Japan
 Nazi Germany surrendered on May 8
 The Americans and British planned to invade Japan on November 1 1945
 However, the invasion would have cost millions of casualties
 On July 26, Allied leaders presented the Potsdam Declaration to Japan

Japan rejected the declaration’s terms of surrender
 In July, Leo Szilard and 70 scientists signed a petition against using the bomb
 Secretary of State James Byrnes prevented Truman from seeing the petition
 Ernest Lawrence wanted the military to publicly demonstrate the bomb
 He reasoned that the show of power would compel Japan to surrender
 However, a failed test would only encourage the Japanese to keep fighting

Only two bombs had been produced after two years and billions of dollars
 It would also remove the element of surprise

Japan might move prisoners of war to bombing targets
 The Scientific Advisory Panel rejected the proposal
 It concluded that direct military use of the bomb remained the only option
 Hiroshima and Nagasaki were selected as targets in summer 1945
 Hiroshima was a major port and housed military headquarters
 It had not been hit with air raids, so the bomb would have a more striking effect
67
68
Manufacturing centers Kyoto and Yokohama were also considered
 Because Kyoto had historical significance as the former capital, it was rejected69
 The seaport and industrial center Nagasaki replaced Kyoto
 On August 6th, 1945, the United States dropped an atom bomb on Hiroshima
 The bomb nicknamed “Little Boy”70 used a gun-type uranium design
 The bomb leveled five square miles of the city and killed 140,000 people
 It released the energy of 15,000 tons of TNT
 The blast sparked firestorms that burned anything not destroyed by the blast
 A radiation flash permanently burned shadows of people and objects onto walls

It etched clothing patterns into skin
 The bomb killed or disabled 90% of Hiroshima’s medical personnel
 President Truman announced the bombing to the American public over radio
 He reasoned that this bomb would “shorten the agony of war”
 If Japan did not surrender, he warned, the United States would drop another bomb
 The United States accordingly dropped a second bomb on Nagasaki on August 9th
 This bomb, named “Fat Man”, was an implosion-type plutonium bomb
 It resembled the Trinity Test’s bomb, releasing 21,000 tons of TNT
 Nagasaki’s geography limited the damage to 3 square miles, killing 74,000 people
 Japan finally surrendered on August 15th
nd
 The formal surrender occurred on September 2 onboard the USS Missouri
 American nuclear research after 1945
 By 1945, the Manhattan Project rivaled the American automotive industry in scale
 It employed 130,000 people and cost $2 billion dollars, or $26 billion in 2015 values
 Many employees did not even know they were working on an atomic weapon
 The National Laboratories set a standard for federally-funded research
 Oak Ridge director Alvin Weinberg termed the federally funded lab system “Big
Science”
 Many reporters predicted that atomic power would transform life after the war
 New York Times journalist William Lawrence termed the period the atomic age
 He had personally witnessed the Trinity Test and the bombing of Nagasaki
 Lewis Strauss thought that electricity would become “too cheap to meter”
 Newspapers and magazines imagined atomic cars and atomic medicine
 The United States did not know if the atomic program should remain controlled by the
military
 In October 1945, Congress debated the May-Johnson Bill
 According to this proposal, the military would continue managing the program
 Fermi and Oppenheimer supported the bill, while Szilard opposed it
 In December 1945, the May-Johnson Bill was replaced by the McMahon Bill
 This bill gave control of the program to civilians
 President Truman signed it into law as the Atomic Energy Act of 1946
 The United States Atomic Energy Commission (AEC) took over the nuclear research
program from the army on January 1st, 1947
 Five civilians sat on the board of the AEC
 It established the National Laboratory system and continued weapons testing

69
70
The Nuclear Regulatory Commission and the Energy Research and Development
Administration replaced the AEC in 1974
 In 1977, Jimmy Carter established the US Department of Energy
 This agency still manages the United States’ nuclear weapons and energy programs
 Nuclear arms race
 The United States and Soviet Union became rival superpowers after World War II
 American scientists predicted that the Soviet Union would develop an atomic bomb in
the 1950s
 The Soviet Union surprised the world by detonating one on August 29, 1949
 The superpowers rapidly grew their stockpiles of nuclear weapons
 Children learned to perform “duck and cover” drills to prepare for nuclear war71
 The next step in atomic escalation involved thermonuclear weapons
 Oppenheimer publicly opposed thermonuclear weapons
 The United States tested a hydrogen bomb on November 1, 1952 in the Pacific
 The Soviets followed suit in August 1953
 If either superpower attacked, both sides would be annihilated
 This situation has become known as mutually assured destruction (MAD)
 Atoms for Peace
 The postwar scientific community experienced rifts and regret
 The United States found out that Germany had not pursued nuclear weapons72
 Many scientists had joined the project for the purpose of pre-empting Germany
 Albert Einstein deeply regretted starting the Manhattan Project
 In 1947, he told Newsweek that he would not have acted had he known Germany
would not develop the bomb
 Oppenheimer told President Truman, “I feel I have blood on my hands”
 He pushed for an international nuclear oversight organization

However, neither superpower wanted to give up nuclear weapons73
 Supporters of disarmament came under suspicion as communist sympathizers
 AEC commissioner Lewis Strauss tried to discredit Oppenheimer

After months of hearings, he had Oppenheimer’s security clearance revoked
 Scientists worked to warn against nuclear weapons while also gaining support for atomic
energy
 Einstein founded the Emergency Committee of Atomic Scientists (ECAS) in 1946
 This group included Leo Szilard and Hans Bethe
 They presented and published information promoting peaceful atomic uses
 In 1945, Eugene Rabinowitch co-founded the Bulletin of the Atomic Scientists
 This non-technical magazine on nuclear weapons exists today as a public reference
on global nuclear issues74
 The Bulletin has published the Doomsday Clock since 1947

The Doomsday Clock measures how close we are to atomic apocalypse

71
72
73
74
Progress of the Doomsday Clock
Period
Minutes from midnight
1947 Height of Cold War Thawing of Cold War January 2016
7
2
17
3
 Eisenhower moved American policy towards peaceful applications of nuclear energy
From MAD to Atoms for Peace
1953
Eisenhower’s December 8 “Atoms for Peace” speech at United Nations
1954
Atomic Energy Act of 1954 partially repeals 1946 Act; allows civilian nuclear power plants
1957
United Nations creates International Atomic Energy Agency (IAEA) to promote
atomic energy and prevent weaponization
1950s60s
Great Britain, France, and China develop nuclear weapons, but have much smaller
stockpiles than the superpowers
1969
Jul 1: United States, Soviet Union, and 60 nations sign Nuclear Non-proliferation Treaty
barring countries from acquiring nuclear weapons
1978
Carter signs Nuclear Non-Proliferation Act preventing the spread of weapons material
but allowing foreign countries to acquire fuel for energy production
All numbers in parentheses refer to the page numbers of the USAD Resource Guide where you
can find the original context of the defined term.
TERMS


Absorption
spectrum (13)
Set of wavelengths absorbed by an atom

 (5)
Aether
Invisible medium that fills the universe; philosophical substance;
does not exist

 vapor (40)
Alcohol
Substance used in cloud chambers

 particle (31, 35, 38, 43)
Alpha
Positively charged decay particle; equivalent to a helium-4
nucleus; can be blocked by paper; travels at 5% of the speed of
light; blocked by skin; ionizing radiation

 momentum (15)
Angular
Property of the electron which Bohr quantized, modifying the
Rutherford planetary model

 (7)
Anode
Positively charged end of a cathode ray tube; receives an invisible
beam from the anode


Antennae
(10)
Objects representing atoms; emit thermal radiation according to
classical physics


Antineutrino
(37)
Antiparticle of the neutrino; released in beta minus decay


Antiparticle
(36)
Relation between the electron and positron

 anemia (34)
Aplastic
Illness caused by radiation exposure; ended Marie Curie's life

 spectroscopy (13)
Atomic
Use of spectral lines to determine a sample's chemical
composition; used in 1868 to discover helium on the sun

 (5)
Atomos
Greek word for "unable to be cut"

 (5)
Atoms
Tiny units of matter; basic building blocks of the universe


Background
radiation (43)
Naturally occurring radiation; affects everyone; mostly from radon

 series (16)
Balmer
Set of hydrogen's spectral lines caused by transition to the n=2
energy level

Betaparticle (35)
Less massive decay particle; can be stopped by aluminum

Big 
Science (68)
Model for federally funded research, as described by Alvin
Weinberg


Bose-Einstein
condensate
(25)
New state of matter composed of particles with integer spin;
created in 1995 by Carl Wieman and Eric Cornell via laser cooling

 (25)
Bosons
Particles with integer spin; unaffected by Pauli exclusion principle


Break-even
(59)
Point at which energy output equals input in fusion reactions


Cathode
(7)
Negatively charged end of cathode ray tube; emits invisible beam


Cathode
ray (7)
Beam of electrons produced by cathode ray tube; travels from the
cathode to the anode


Chernobyl
accident (54)
Worst nuclear power incident in history on April 26, 1986 in the
Soviet Union; released 400 times more radiation than Hiroshima

 (23)
Cloud
Metaphor for arrangement of electrons in the Schrödinger model


Coherent
(26)
Property of laser light; light waves travelling in phase; creates
good interference patterns


Corpuscule
(6)
Theoretical infinitely divisible particles proposed by Isaac Newton

 rays (43)
Cosmic
High energy radiation originating from outside the solar system

 (49)
Critical
Situation with constant number of fission events; K = 1

 (34)
Crystals
Subject studied by Pierre Curie before joining his wife's research

 (5)
Cube
Shape associated with earth by Plato


Daughter
nucleus (36)
Nucleus produced by radioactive decay


Deterministic
(22)
A Newtonian view of the world


Diamagnetic
(24)
Materials composed of paired electrons; repelled by magnetic
fields


Directional
(26)
Property of laser light; light travelling in a uniform direction

DNA(43)
Cellular component damaged by ionizing radiation; contributes to
mutations, disorders, and cancer


Electromagnetic
spectrum (9)
Range of all possible electromagnetic waves


Electron
(7, 14, 20)
Negatively charged cathode ray particle 1800 times lighter than
hydrogen; atomic component; discovered by J.J. Thomson; resides
at quantized energy levels; releases energy when moving down a
level; used in transmission and scanning electron microscopes


Emission
spectrum (13)
Set of wavelengths emitted by excited electrons


Endothermic
(47)
Reaction which consumes energy; Q < 0

 state (16)
Excited
Energy levels above the ground state


Exothermic
(47)
Reaction which releases energy; Q > 0


Fermion
(24)
Particles with half-integer spin; includes electrons; two of these
cannot occupy the same quantum position


Ferromagnetic
(24)
Materials with at least one unpaired electron; includes iron and
nickel; loses magnetic properties above the Curie temperature

 (47)
Fissile
Nuclei that perform fission after colliding with low-energy
neutrons

 products (47)
Fission
Output of a fission reaction


Fissionable
(48)
Nucleus that only performs fission with fast neutrons

Freeradical (43)
Neutral atom with unpaired electrons; created by radiation; forms
harmful compounds in the body


Fukushima
Daiichi nuclear
accident (54)
Nuclear disaster following an earthquake on March 11th, 2011;
forced evacuations of the surrounding area

 ignition (58)
Fusion
Point at which a fusion reaction becomes self-sustaining

 particle (35, 43)
Gamma
Photon decay particle; high energy; can only be stopped by lead
plating; most destructive to life


Graphite
(51, 61)
Moderator in first nuclear reactor; made of carbon-12; purchased
in the early days of atomic research

 state (15)
Ground
Lowest allowable energy state of an atom or particle

 water (51)
Heavy
Water with two molecules of deuterium instead of hydrogen; used
as a moderator in Canadian reactors


Ionizing
radiation (42)
Radiation with enough energy to remove electrons from atoms;
energy > 10 eV; includes X-rays, gamma rays, UV light, alpha
particles, beta particles, and decayed neutrons


Icosahedron
(5)
Shape associated with water by Plato


Isotopes
(30)
Atoms with the same number of protons but different numbers of
neutrons; means "the same place" in Greek

 series (16)
Lyman
Set of hydrogen's spectral lines discovered from 1906 to 1914


Magnetic
moment (24)
Property of the electron; measures tendency to align with a
magnetic field


Magnetic
resonance imaging
(34)
Using power magnetics and radio waves to perform diagnostic
imaging of patients


Moderator
(50)
Component of a nuclear reactor; surrounds the nuclear fuel and
slows down fast neutrons


Monochromatic
(26)
Property of laser light; light of a uniform frequency

 (40)
Muon
Particle discovered in a cloud chamber

NaI 
(40, 45)
Crystal used in scintillation counters; ingested by patients when
using radioactive tracers


Neutrino
(37, 43)
Particle released in beta plus decay; first observed in 1950; has no
electric charge and very little mass; does not interact with matter


Neutron
(29)
Electrically neutral particles in the nucleus; a type of nucleon;
proposed in 1920 by Ernest Rutherford


Non-ionizing
radiation (42)
Radiation without enough energy to remove electrons from
atoms, e.g. radio waves, microwaves, infrared, and visible light

 physics (29)
Nuclear
Study of the structure and behavior of the atomic nucleus


Nucleon
(29)
Particle in the nucleus; proton or neutron


Nucleus
(7)
Dense central core of the atom; contains protons and neutrons;
positively charged


Paramagnetic
(24)
Materials composed of unpaired electrons; have an overall
magnetic moment

 nucleus (36)
Parent
Nucleus performing radioactive decay


Paschen
series (16)
Set of hydrogen's spectral lines discovered in 1908

 (13)
Photon
Particle form of light; first proposed by Albert Einstein; massless,
yet still carries momentum


Pitchblende
(34)
Mineral which contains uranium; studied by Marie Curie

 (58)
Plasma
Collection of superheated atoms represented by a cloud


Positron
(36, 40)
Antiparticle of the electron; same mass as electron but opposite
charge; very short lifetime outside of a vacuum; discovered in a
cloud chamber


Primordial
isotopes (44)
Isotopes created with the Earth; includes uranium-238


Probabilistic
(22)
A quantum view of the world


Probability
density (20)
Field of probabilities where a particle may reside'

 (29)
Proton
Positively charged particle in the nucleus; a type of nucleon


Psi (20)
Greek letter denoting wave functions


Quantum
(11)
A discrete, fundamental unit of energy


Quantum
mechanics (19)
Field of physics which provided a unified explanation for quantum
effects; rose in prominence after 1925


Radiation
therapy (43)
Using targeted ionizing radiation to kill cancerous cells


Radioactive
waste (52)
Harmful radioactive fission products of uranium-235


Radiometric
dating (44)
Using the half-life of isotopes in a substance to determine its age;
developed by Willard Libby in the 1940s


Subcritical
(49)
Situation of decreasing number of fission events over time; K < 1


Sunburn
(43)
Radiation damage caused by exposure to ultraviolet radiation
from the sun


Supercritical
(49)
Situation in which the number of fission events increases
exponentially with time; K > 1; used in nuclear weapons


Thermal
radiation (10)
Radiation emitted by objects above 0 K; generally felt as infrared
radiation

 Mile Island accident
Three
(53)
Nuclear accident on March 28 1979 in Pennsylvania; worst nuclear
accident in American history but did not have any health impacts


Torbernite
(34)
Mineral containing uranium; studied by Marie Curie

 (45)
Tracer
Radioactive substance used to track how chemicals participate in
reactions and flow through a system


Uranium
hexafluoride (50)
Gas used in gas diffusion enrichment

 (34)
X-rays
High energy rays named by Wilhelm Roentgen for their unknown
nature
Units and Constants

 mass number (29)
Atomic
A; total number of neutrons and protons in the nucleus

 number (29)
Atomic
Z; the number of protons in the nucleus; indexes the elements


Becquerel
(39)
Standard unit of radioactivity since 1975; 1 decay per second

 energy (32)
Binding
Energy required to split a nucleus apart into neutrons and
protons; indicates the stability of an atom; peaks around Z=56

Bohrradius (15)
0.0529 nm; radius of ground state electron orbit in hydrogen atom

 of the proton (29)
Charge
1.6 × 10−19 coulombs

 mass (54)
Critical
Minimum mass of fissile material for a chain reaction; for
weapons-grade uranium-238, a sphere 6.8 inches in diameter

 temperature (24)
Curie
Upper limit at which ferromagnets have magnetic properties

 temperature (39)
Curie
Standard unit of radioactivity until 1975; 3.7 × 10−10 decays/s

 constant (38)
Decay
λ; corresponds to speed of decay for an isotope

 rate (39)
Decay
Also known as radioactivity; decays per second


Electron
volt (15)
1.6 * 10^-19 J; energy of an electron accelerated by a 1 volt
potential difference

 level (14)
Energy
A specific, quantized, stable orbit of the electron


Femtometer
(30)
10−15 meters; the approximate radius of a nucleus

 (30)
Fermi
See femtometer


Frequency
(9)
Speed of oscillation of a wave; measured in hertz

 (39)
Half-life
Time for half of a sample of an isotope to decay; quantifies atomic
stability

 (9)
Hertz
Measures frequency of waves; equal to 1 oscillation per second


Ionization
energy (16)
Energy required to completely remove an electron from an atom;
for hydrogen, 13.6 eV

 numbers (33)
Magic
Recurring numbers of neutrons and protons which contribute to
stability; 2, 8, 20, 28, 50, 82, 126


Momentum
(13)
Property of objects with mass and photons


Multiplication
factor K (49)
Average number of neutrons released in a fission event that will
trigger another fission event; controls criticality


Nanosecond
(12)
Delay before electron ejection in the photoelectric effect


Neutron
number (29)
N; the number of neutrons in the nucleus

 magnetic quantum
Orbital
number (24)
𝑚𝑙 ; can be integer values from -l to +l; associated with the
Zeeman effect

 quantum number
Orbital
(24)
𝑙 ; can be non-negative integer values

 constant (11)
Planck's
6.63 × 10−34 Joule seconds; central in quantum mechanics


Principal
quantum number
(24)
See quantum number

 (46)
Q value
The energy released by one nuclear reaction event; the difference
in mass between products and reactants


Quantum
number (15, 23)
Index of electron energy; only positive integers; represented by n

 atomic mass (29)
Relative
Mass number listed on periodic tables; average mass of all
isotopes of an element weighted by abundance

Rem(42)
Measure of dosage commonly used in the United States; equals
1/100 sievert


Rydberg
constant (14)
1.097 × 107 𝑚−1

 (27)
Second
Unit defined in 1967 as the time of 9,192,631,770 oscillations of
cesium-133 through its energy states; most accurate SI unit

 (42)
Sievert
Measures dosage of ionizing radiation; represents the effect of 1
joule of radiation on 1 kg of absorbing material

Spinquantum number (24)
𝑚𝑠 ; for electrons, can be +1/2 or -1/2


Temperature
(27)
Measures a substance's kinetic energy


Threshold
energy (47)
Minimum kinetic energy required for an endothermic reaction

 mass unit (29)
Unified
u; 1/12 the mass of a carbon-12 atom; the mass of one proton or
one neutron; 1.66 ∗ 10−27 kg


Wavelength
(9)
Distance between successive peaks in a wave
Equations

 mass number (29)
Atomic
A; total number of neutrons and protons in the nucleus

 decay reaction (36)
Alpha
→

Betanegative decay reaction
(36)
𝐴
𝑍𝑋
𝐴
𝑍𝑋
→
𝑍−4
𝑍−2𝑌
𝐴
𝑍+1𝑌

Betaplus decay reaction (36)
𝐴
𝑍𝑋
→
𝐴
𝑍−1𝑌


de Broglie
hypothesis (17)
𝜆=

 rate equation (39)
Decay
𝑅 = 𝑅0 𝑒 −𝜆𝑡


Differential
wave equation
(19)
Classical equation; describes behavior of macroscopic waves


Einstein's
relation (29, 32)
𝐸 = 𝑚𝑐 2; explains mass difference between nucleon and nuclear
weights

 levels in hydrogen
Energy
(15)
𝐸𝑛 = 13.6


Exponential
decay (38)
𝑁 = 𝑁0 𝑒 −𝜆𝑡

 decay reaction (37)
Gamma
𝑋∗ → 𝑋 + 𝛾

Halflife equation (39)
𝑡ℎ =
+ 42𝐻𝑒
+ 𝑒−
+ 𝑒+
ℎ
𝑝
ln 2
𝜆
𝑒𝑉
𝑛2


Heisenberg
uncertainty
principle (23)
Δ𝑥Δ𝑝 ≥ 2𝜋 ; stipulates that momentum and position of a particle


Lawson’s
criterion (58)
nτ > some number for plasma to occur; n = plasma ion density; t
= plasma confinement time


Newton's
laws of motion (19)
Classical laws; describe the behavior of macroscopic particles

 notation (29)
Nuclear
𝐴
𝑍𝑋;

 relationship (11)
Planck's
𝐸 = 𝑛ℎ𝑓; relationship between energy of an oscillating particle
and its frequency

of electrons in
Radii
hydrogen (15)
𝑟𝑏 = 𝑛2 𝑎0

 of the nucleus (30)
Radius


Schrödinger
equation (19)
1925 description of matter waves’ behavior; cannot be derived
from fundamental equations: purely based on experimental results

The
Rydberg formula (14)
1
ℎ
cannot both be known
A = mass number; Z = atomic number
1
𝑟 = 𝑟0 𝐴3
𝜆
= 𝑅𝐻 (
1
𝑚2
hydrogen

 functions (20, 23)
Wave
−
1
𝑛2
); describes the wavelengths of spectral lines in
Solutions to the Schrödinger equation; labeled by the Greek letter
psi; describes electrons in the Schrödinger model
Elements and Isotopes


Actinium
(39)
Element which can enter a decay chain


Aluminum
(27)
Element used in atomic clocks


Americium-231
(44)
Isotope in smoke detectors; alpha-decays into neptunium-1237

 (44)
Argon
Element used in radiometric dating

 (48)
Barium
Half as massive as uranium; bombarded by Otto Hahn and Fritz
Strassman; can be produced in fission of uranium-235


Beryllium
(31)
Discovered ca. 1930; emits radiation if struck with alpha particles


Bismuth-212
(39)
Isotope produced in decay chain of thorium

 (51)
Boron
Neutron-absorbing material used in control rods


Californium
(31)
All isotopes heavier than this element do not occur naturally


Carbon-12
(29, 51)
Isotope used to define the unified mass unit; found in graphite


Carbon-14
(36, 44)
Isotope which decays into nitrogen-14 through beta decay;
measured in radiometric dating


Cesium-133
(27)
Isotope used in atomic clocks; defines the second in the SI system


Cobalt-60
(43)
Isotope used in food irradiation


Deuterium
(31, 50, 58)
Isotope of hydrogen with a proton and neutron; useful moderator;
used in fusion; found in seawater


Fluorine
(50)
Element combined with uranium in gas diffusion enrichment

 (7)
Gallium
Element predicted by Mendeleev's periodic table before its
discovery; "doubly magic"; has high atomic stability


Helium-4
(13,24, 25, 32, 55)
Isotope discovered using atomic spectroscopy in 1868; found on
the sun; a noble gas; used in lasers; produced in nuclear fusion


Hydrogen
(6, 14, 27, 34, 40,
58)
Element discovered by Antoine Lavoisier and modeled by the
Rydberg formula; used in atomic clocks and bubble chambers;
aligned by magnetic waves in magnetic resonance imaging;
undergoes fusion; lightest and most abundant element


Iodine-131
(45)
Radioactive isotope used in radioactive tracing; synthetic

Iron(24, 32)
Ferromagnetic material; very stable element

 (48)
Krypton
Element produced in the fission of uranium-235

Lead(35)
Element used to shield against gamma radiation

 (24)
Lithium
An alkali metal


Lithium-7
(46)
Isotope used by Ernest Walton and John Cockcroft in the first
nuclear reaction


Mercury
(17, 27)
Element used in James Franck and Gustav Hertz's experiment with
a vacuum tube; used in atomic clocks

 (24, 25)
Neon
Noble gas used in lasers


Neptunium
(39, 48)
Artificial element; can enter a decay chain; discovered by Enrico
Fermi by bombarding uranium

 (18, 24, 32)
Nickel
Element used in the Davisson-Germer experiment which proved
wave-particle duality; ferromagnetic material; very stable element


Nitrogen-14
(30, 56)
Gas used by Ernest Rutherford in observing the emission of
hydrogen nuclei after nuclear collisions; produced in the beta
decay of carbon-14; present in the CNO cycle

 (6, 32, 56)
Oxygen
Element initially discovered by Antoine Lavoisier; "doubly magic";
has high atomic stability; present in the CNO cycle


Phosphorous
(37)
Element studied by Irene Joliot-Curie and her husband Frederic


Plutonium-239
(48, 52, 64)
Discovered by Enrico Fermi by bombarding uranium; carcinogenic;
used in nuclear weapons; produced in breeder reactors; desired
product of the Hanford Engineer Works; cannot be used in guntype weapons; powered Fat Man bomb


Polonium
(34)
Element discovered by Marie Curie and Pierre Curie


Potassium-40
(42)
Isotope which provides an annual dose of 0.4 mSv if ingested


Radon-222
(43)
Isotope responsive for most background radiation; causes lung
cancer; found as a dense inert gas


Rubidium
(27)
Gas cooled to 50 trillionth K by Stanford researchers in 2015

 (24, 51)
Sodium
Alkali metal whose emission spectrum has split lines; used in
liquid form as reactor coolant


Strontium
(27, 48)
Element used in atomic clocks; produced in uranium-235 fission


Tellurium
(36)
Lightest known element to perform alpha decay


Thorium
(39)
Element which can enter a decay chain


Thorium-234
(36)
Isotope produced by the alpha decay of uranium-238

 (31)
Tritium
Radioactive isotope of hydrogen with two neutrons and a proton


Uranium
(48)
Heaviest known element in the 1930s


Uranium-235
(48, 67)
Isotope that produces a usable chain reaction; releases three
neutrons during each fission; powered the Little Boy bomb


Uranium-238
(34, 40, 49)
Radioactive isotope studied by Marie Curie; alpha-decays into
thorium-234 decay chain and replenishes the natural abundance
of radium-226; absorbs neutrons without performing fission

 (48)
Xenon
Element produced in the fission of uranium-235
Theories and Phenomena

 decay (36)
Alpha
Decay involving the emission of a helium nucleus

 theory (5)
Atomic
Theory that all matter is composed of indivisible atoms

Betadecay (36)
Decay involving the emission of an electron or positron

Betaminus decay (36)
Decay involving the emission of an electron

Betaplus decay (36)
Decay involving the emission of a positron

 reaction (48)
Chain
Neutrons from one fission event triggering more events

CNOcycle (56)
Reactions in very hot, large stars; converts hydrogen to helium via
carbon, nitrogen, and oxygen; proposed by Hans Bethe in 1939


Compton
scattering (13)
Discovered in 1923; scattering of X-ray radiation off free electrons;
unexplainable by the wave model of light and classical physics


Corpuscular
theory (6)
Theory that all matter contains infinitely divisible corpuscules


Corpuscular
theory of light
(7, 9)
Isaac Newton’s theory in Opticks (1704) that light consists of
weightless balls; explains reflection but not refraction or
diffraction


Correspondence
principle
(16)
Proposed by Niels Bohr; states that quantum theory should align
with classical expectations at large scales


Coulomb
barrier (55)
Energy barrier preventing fusion reactants from colliding


Dalton's
atomic theory (6)
Principles in John Dalton’s 1808 A New System of Chemical
Philosophy stating that identical atoms comprise an element;
atoms cannot be created, destroyed, or divided, and (re)combine
in simple ratios in chemical reactions


de Broglie
hypothesis (17)
Relation of a particle's momentum with its wavelength

 (39)
Decay
Transformation of parent isotopes to daughter isotopes through
the emission of alpha, beta, or gamma particles

 chain (39)
Decay
Radioactive daughter nucleus performing more decay; occurs with
thorium, uranium, actinium, and neptunium


Doppler
cooling (27)
Method of selectively slowing atoms in laser cooling


Doppler
effect (27)
Frequency shift caused by relative motion between the observer
and wave emitter; used in laser cooling

 slit interference (9)
Double
Discovered by Thomas Young in 1803; constructive and
destructive interference formed when light enters two narrow slits


Electron
capture (37)
Absorption of an orbiting electron by a nucleus; emits a neutrino


Enrichment
(49)
Increasing proportion of uranium-235 in mined uranium

 (65)
Fizzle
Situation in which a nuclear weapon prematurely detonates
without reaching its expected yield

 decay (37)
Gamma
Process in which a nucleus transitions from a high energy to a low
energy state and releases a gamma ray photon


Heisenberg
uncertainty
principle (23)
Axiom that the position and momentum of a particle cannot both
be known with absolute precision


Induced
radioactivity (37)
Artificial creation of an unstable isotope artificially

 confinement fusion
Inertial
(59)
Using high-power lasers to heat and compress a pellet of
deuterium and tritium to start fusion; utilized by the NIF


K-capture
(37)
Form of electron capture that absorbs it from the "K" shell

 cooling (27)
Laser
Using lasers to slow atoms; draws on photon momentum

Law
of conservation of
matter (6)
Observation that mass is conserved in chemical reactants; noted
by Antoine Lavoisier in the late eighteenth century


Maxwell's
theory of
electromagnetism (9)
Description of light as a wave made up of oscillating electric and
magnetic fields


Meltdown
(41)
Result when the core of a nuclear reactor overheats and melts


Mutually
Assured
Destruction (69)
Scenario in which states completely destroy each other in mutual
nuclear weapon attacks

 fission (47)
Nuclear
Heavy nucleus splitting into two lighter nuclei and releasing
energy; triggered by collisions

 fusion (55)
Nuclear
Two small nuclei colliding to form a larger nucleus

 reaction (46)
Nuclear
Two nuclei colliding to form different nuclei; analogous to
chemical reactions

Pauliexclusion principle (24)
Axiom that no two electrons have the same set of quantum
numbers, except for bosons


Photoelectric
effect (12)
First observed by Heinrich Hertz in 1887; release of electrons by
metals illuminated with ultraviolet light


Planetary
model (7)
Model of the atom inspired by Rutherford’s discovery of the
nucleus; electrons orbiting a dense positively charged nucleus

pudding model (7)
Plum
Model of the atom proposed by J.J. Thomson; featured a sea of
electrons suspended in a positively charged sphere


Population
inversion (25)
Creation of sample with more excited atoms than in the ground
state


Proton-proton
chain (56)
Multi-step solar fusion reaction; converts four protons into
helium-4, positrons, neutrinos, and gamma rays; proposed by
Hans Bethe in 1939


Quantum
theory (9)
Theory that energy and matter is quantized


Quantum
tunneling (20, 55)
Implication of the Schrödinger equation that low energy particles
can overcome tall potential barriers; basis for scanning tunneling
microscope; lets particles in nuclear fusion cross Coulomb barrier


Radioactive
decay (35)
Spontaneous emission of radiation associated with a
transformation from an unstable nucleus to a stable nucleus


Radioactivity
(34)
Spontaneous radiation emission; studied by Curies and Becquerel


Refraction
(9)
Light bending around narrow apertures or corners


Schrödinger
model (23)
Model of the atom which describes electrons with wave functions;
features a "cloud" of electrons; the modern model of the atom

wind (56)
Solar
Collection of low mass particles ejected by the Sun


Spontaneous
emission (25)
An atom releasing a photon in a random direction


Stimulated
emission (25)
Causing atom to transition to a lower energy level and release a
photon; used in lasers

 nuclear force (32)
Strong
Attractive force between nucleons; counteracts repulsive force
between protons


Thermonuclear
fusion (55)
Fusion of nuclei at extremely high temperatures


Ultraviolet
catastrophe (11)
Finding that blackbody radiation emits little ultraviolet light


Wave-particle
duality (18)
Notion that light and matter exhibit properties of both waves and
particles; seen in double slit experiment


Zeeman
effect (24)
Fine splitting of spectral lines when substance is placed in a
magnetic field
Devices

 clock (27)
Atomic
Timekeeping device; relies on precise frequencies of atomic
transitions


B Reactor
(64)
First plutonium-generating reactor; located at Hanford Engineer
Works


Blackbody
(10)
Idealized object that releases all radiation it absorbs to remain in
thermal equilibrium

 water reactor (52)
Boiling
Reactor using water as moderator, coolant, and source of steam

 reactor (52)
Breeder
Reactor producing useful fissile material, plutonium-239

 chamber (40)
Bubble
Traces the path of ionizing radiation; uses liquid hydrogen;
invented by Donald Glaser in 1952


Cathode
ray tube (7)
Device consisting of glass tubes with vacuums; creates a cathode
ray; used in CRT televisions and computer monitors; used in many
experiments in the 1800s

 chamber (40)
Cloud
Traces path of ionizing radiation; uses saturated vapor and piston

 rod (51)
Control
Component of a nuclear reactor; absorbs neutrons and regulates
the speed of the chain reaction


Cyclotron
(62)
First particle accelerator; invented by Ernest O. Lawrence


Doomsday
Clock (69)
Concept created by the Bulletin of the Atomic Scientists; measures
how close the world is to nuclear Armageddon

 Reactor (52)
EBR-1
First reactor to generate electricity in 1951; located in Idaho,


Fat Man
(67)
Plutonium implosion nuclear weapon; dropped on Nagasaki

Gas
centrifuge (50)
Uses rapidly rotating cylinder to separate uranium-235 from
uranium-238

Gas
diffusion enrichment
(50)
Uses semi-permeable membranes to separate uranium-235 from
uranium-238

 counter (40)
Geiger
Radiation detector; uses tube of inert gas; creates clicking sound


Generation
IV reactor (53)
Next generation nuclear reactor design; minimizes waste,
enhances safety, and prevents nuclear proliferation

Goldfoil apparatus (7, 30)
Device which Ernest Rutherford, Hans Geiger, and Ernest Marsden
used to discover the nucleus; contained a beam of positive alpha
particles which deflected off a gold foil


Gun-type
(54)
Detonation mechanism where two pieces of fuel are shot together

 laser (26)
HeNe
Common laser used in laboratories and classrooms


Implosion-type
(54)
Detonation mechanism in which explosives compress a subcritical
fuel mass; used in modern nuclear weapons

ITER(59)
World's largest experimental fusion reactor; funded by 7 countries

JointEuropean Torus (59)
Tokamak fusion reactor located in the UK

K-25(63)
Gaseous diffusion plant at Oak Ridge; one of the largest singleroofed buildings in the world

 Hadron Collider at
Large
CERN (46)
Advanced particle accelerator capable of accelerating particles to
energies greater than 1 TeV

 (26)
Laser
Device using stimulated emission to create a beam of
monochromatic, directional, coherent light

 enrichment (50)
Laser
Uses tuned lasers to separate uranium-235 from uranium-238;
requires little energy

Boy (67)
Little
Uranium gun-type nuclear weapon; dropped on Hiroshima


Magnetic
separation
enrichment (50)
Uses a magnetic field to separate uranium-235 and uranium-238


National
Ignition Facility (59)
Largest ICF device in the world; at Lawrence Livermore National
Labs in California; uses lasers to compress a hydrogen pellet

 reactor (50)
Nuclear
Device which initiates and controls a nuclear chain reaction;
harnesses reaction energy for power generation

 in a box (20)
Particle
Physics model which describes an energized particle trapped in a
1 dimensional space bounded by infinitely high potential walls


Photomultiplier
tube (40)
Component of a scintillation counter

 (63)
Pile-1
Enrico Fermi's first nuclear reactor; built at the University of
Chicago


Pressurized
water reactor
(52)
Reactor which uses a separate cooling loop of water to produce
steam; common in the United States; prevents fuel leakage


Proportional
counters (40)
Sophisticated form of Geiger counters; measures energy of
radiation


Scanning
tunneling
microscope (20)
Uses quantum tunneling to achieve resolutions of 0.1 nm using
electrons


Schrödinger's
cat (22)
Scenario involving a simultaneously dead and alive cat;
demonstrates the multiple states of a quantum system


Scintillation
counter (40)
Radiation detector; relies on NaI crystal and a photomultiplier
tube; can determine the energy of emitted radiation

 detector (44)
Smoke
Device using a stream of alpha-particles produced by americium241


Thermonuclear
weapon (57)
Nuclear weapon which uses a fission bomb to trigger a
thermonuclear explosion

ThinMan (65)
Gun-type plutonium fission bomb; abandoned due to poor quality
of available plutonium


Tokamak
(58)
Toroidal shaped device that confines a plasma using magnetic
fields; developed in the Soviet Union during World War II


Tokamak
Fusion Test Reactor
(TFTR) (59)
Tokamak fusion reactor at Princeton; never reached break-even


Transmission
electron
microscope (18)
Device which relies on the wave properties of electrons to achieve
very fine image resolutions; accelerates electrons to 100 keV; has a
resolution on the order of 0.0037 nm

 Bomb (65)
Trinity
First nuclear weapon ever detonated; implosion-type

TsarBomba (57)
Most powerful nuclear weapon detonated; a hydrogen bomb; as
powerful as 50 million tons of TNT

 Missouri (67)
U.S.S.
Ship which hosted the former surrender of Japan

X-10(63)
Graphite reactor at Oak Ridge

Y-12(63)
Electromagnetic separation plant at Oak Ridge; second manmade
nuclear reactor
Awards and Publications

Nobel Prize in Physics
1901
(34)
First Nobel Prize in Physics; awarded to Wilhelm Roentgen for
discovering X-rays

Nobel Prize in Physics
1903
(34)
Awarded to Marie Curie, Pierre Curie, and Henri Becquerel for
their discoveries involving radioactivity

Nobel Prize in
1911
Chemistry (34)
Awarded to Marie Curie, Pierre Curie, and Henri Becquerel for
their discoveries involving radioactivity

Nobel Prize (13)
1921
Awarded to Albert Einstein for explaining the photoelectric effect
using photons

Nobel Prize in Physics
1925
(17)
Awarded to James Franck and Heinrich Hertz for demonstrating
that an atom's absorption energies match its emission energies

Nobel Prize in
1935
Chemistry (38)
Awarded to the Joliot-Curies for discovering induced radioactivity

Nobel Prize in
1960
Chemistry (44)
Awarded to Willard Libby for developing carbon dating

Nobel Prize (57)
1967
Awarded to Hans Bethe for explaining stellar energy production

Nobel Prize in Physics
1997
(27)
Awarded to three physicists for developing laser cooling

 System of Chemical
A New
Philosophy (6)
Published in 1808 by John Dalton; included Dalton's basic atomic
principles

 Energy Act of 1946
Atomic
(68)
Placed atomic research under civilian control; passed by Harry
Truman

 Energy Act of 1954
Atomic
(69)
Signed by Eisenhower; permitted the development of civilian
nuclear power plants

 for Peace (69)
Atoms
Address delivered by President Eisenhower to the United Nations;
outlined a commitment to peaceful atomic uses

 of the Atomic
Bulletin
Scientist (68)
Non-technical magazine on nuclear weapons and nuclear security
founded by Eugene Rabinowich; source of the Doomsday Clock


May-Johnson
Bill (68)
Bill proposed in October 1945; would continue military oversight
over atomic research; opposed by Szilard


McMahon
Bill (68)
Bill proposed in December 1945 to oppose the May-Johnson Bill;
placed atomic research under civilian control; incorporated in the
Atomic Energy Act of 1946

Mr. 
Tompkins in Wonderland
(23)
Written in 1940 by George Gamow; describes a bank teller
exploring a quantum jungle with strange animals

NewYork Times (68)
Newspaper of William Lawrence


Newsweek
(69)
Quoted Einstein's opposition to the Manhattan Project

 Non-Proliferation
Nuclear
Act of 1978 (69)
Signed by President Carter; prevented the spread of nuclear
materials for weapons use, but allowed for peaceful use

 Non-Proliferation
Nuclear
Treaty (69)
Signed in 1968 by 69 nations; prevented new nations from
acquiring nuclear weapons

 (6, 9)
Opticks
Published in 1704 by Isaac Newton; suggested the corpuscular
theory of light


Periodic
Table of Elements
(6)
Organization system for elements created by Dmitry Mendeleev;
organized elements by atomic weight


Potsdam
Declaration (66)
Allied leaders present terms of surrender to Japan
Numbers

-1/2(24)
Possible spin quantum number value for electrons

 20, 25)
0 (10,
Minimum temperature in Kelvin for a body to release thermal
radiation; absolute 0 in Kelvin; classical probability that a particle
will cross a high potential wall; temperature of the Bose Einstein
condensate

6.63× 10−34 (11)
Value of Planck's constant in Joule-seconds

 (42)
10−33
Energy above which radiation is considered ionizing, in eV

10−31 (30)
9.1 ×
Mass of one electron, in kilograms

1.66× 10−27 (29)
Mass of one unified mass unit, in kilograms; mass of a proton or
neutron, in kilograms

 (13)
10−19
Approximate energy of a photon in Joules

10−19 (15, 29)
1.6 ×
Energy of an electron accelerated across a 1-volt potential
difference in Joules; charge of a proton in Coulombs

 (30)
10−15
Approximate nuclear radius in meters; 1 femtometer, in meters

1/50trillion (27)
Temperature in Kelvin to which Stanford researchers were able to
supercool rubidium in 2015

 (30)
10−14
Rutherford's estimate of the nuclear radius, in meters


1 trillionth
(44)
Portion of carbon that is carbon-14

 (30, 35)
10−10
Radius of an atom's electron cloud in meters; lifespan of a
positron in seconds

10−9(59)
Time it takes for the NIF to achieve ignition, in seconds

 × 107 (14)
1.097
Value of the Rydberg constant in m^-1

1/70thousand (27)
Average velocity of molecules in the supercooled rubidium
produced by Stanford researchers, in mm/s

 × 10−4 (30)
5.486
Mass of one electron, in unified mass units

 (18)
0.0037
de Broglie wavelength of electrons in a transmission electron
microscope in keV

0.02millisieverts (42)
Dosage of a chest X-ray

 nanometers (15)
0.0529
Value of the Bohr radius

 53)
0.1 (22,
Resolution of a scanning tunneling microscope; annual dosage to
a person living 50 miles from a nuclear power plant, in
microsieverts

1/3 
(53)
Fraction of the world's nuclear energy produced by the United
States


0.4 (42)
Dosage of potassium-40 if ingested in millisieverts

0.4 -0.7 (22)
Distance from the sample in a scanning tunneling microscope in
nanometers

1/2 
(24)
Possible spin quantum number value for electrons

 (30)
0.511
Mass of one electron in mega-electron volts


0.7 (49)
Percent abundance of uranium-235 in nature

 42, 44, 46)
1 (12,
Number of nanoseconds delay before electron ejection in the
photoelectric effect; dosage which causes radiation sickness, in
sieverts; quantity of americium-241 in a smoke detector, in
micrograms; scale of the energy released by one nuclear reaction,
in MeV

 33, 34, 35, 59, 67, 69)
2 (16,
Associated with the Balmer series; a magic number; Nobel Prizes
awarded to Marie Curie; Denver receives this times more radiation
annually than the national average; size of the pellet employed by
the NIF, in mm; billions spent by the Manhattan Project; least
minutes the Doomsday Clock has been from midnight

2 - 3(14)
Transition of the hydrogen electron which produces red light


2.5 (48)
Average number of neutrons released by fission of uranium-235

 69)
3 (48,
Maximum number of neutrons released by fission of uranium-235;
current setting of the Doomsday Clock in minutes from midnight

3 - 4(49)
Percent abundance of uranium-235 in nuclear fuel

4 (5,42)
Basic elements as envisioned by Plato; minimum


4.9 (17)
Energy lost by an electron colliding with mercury in eV

5 (6,35, 42, 66)
Fatal radiation dosage in sieverts; principles in Dalton's atomic
theory; percent of the speed of light which an alpha particle
travels at; depth in feet of the Trinity test crater


6.2 (42)
Average background annual dosage in the United States, in
millisieverts


6.8 (54)
Size of a critical mass sphere of weapons grade uranium, in cm

 69)
7 (59,
Members of ITER; minutes to midnight at Doomsday Clock’s
creation


7.5 (66)
Height in miles of the Trinity mushroom cloud


7.6 (49)
Average binding energy per nucleon in uranium-235, in
MeV/nucleon

 42)
8 (33,
Magic number; lethal dosage of radiation, in sieverts


8.5 (49)
Average binding energy per nucleon in medium-sized fission
products, in MeV/nucleon


9 (41)
Magnitude of the earthquake which triggered the Fukushima
Daiichi nuclear accident

 62)
10 (58,
Half-life of tritium, in years; original estimate of uranium-235
critical mass

10.4(57)
Energy release of the first hydrogen bomb, in megatons TNT

 (52)
10.9%
World's energy production generated by nuclear reactors

13.6(16)
Ionization energy of hydrogen in eV

 62)
15 (7,
Diameter of shell mentioned by Rutherford when he commented
on the results of the gold foil experiment; time it took for
President Roosevelt to approve the NDRC, in minutes

 (52)
19.5%
United States' energy production generated by nuclear reactors


20 (33)
Mass number below which stable atoms contain equal numbers of
neutrons and protons; a magic number

23.5(52)
Half-life of uranium-239, in minutes

 (56)
24.68
Energy released in the proton-proton chain, in MeV


25 (56)
Abundance of helium in the Sun by mass percent


26 (67)
Total budget of the Manhattan project, in billions of 2015 dollars


28 (33)
A magic number

 52, 58, 66)
30 (13,
Countries operating nuclear reactors as of 2015; liters of seawater
required to collect 1g of deuterium; width in feet of the Trinity test
crater

 33, 57)
50 (22,
Probability that Schrödinger's cat is dead or alive; a magic
number; energy release of Tsar Bomba, in millions of tons of TNT


56 (32)
Mass number with maximum atomic stability


60 (32)
Mass number above which binding force decreases


62 (69)
Countries which signed the Nuclear Non-Proliferation Treaty


64 (6)
Elements known to Dmitri Mendeleev


70 (66)
Scientists who signed Leo Szilard's petition to demonstrate the
bomb to the Japanese


74 (56)
Abundance of hydrogen in the Sun by mass percent

75%(52)
France's energy production generated by nuclear reactors


82 (33)
A magic number


83 (33)
Mass number above which no stable isotopes exist


85 (62)
Amount of money obtained by Vannevar Bush for the purpose of
constructing uranium enrichment plants, in millions of dollars

 49)
90 (7,
Degrees some particles were deflected in the gold foil experiment;
percent abundance of uranium-235 in nuclear weapons

 48)
92 (29,
Protons in uranium-238; atomic number of uranium


93 (48)
Atomic number of neptunium


94 (48)
Atomic number of plutonium


98 (31)
Mass number of californium

 (31)
99.99%
Proportion of hydrogen-1 in all isotopes of hydrogen

100
(18, 42, 48, 64)
Rems in a sievert; dose above which cancer risks increase, in
millisieverts; energy of a fission reaction, in MeV; height of the
steel tower used in the Trinity test, in feet; energy of electrons in a
transmission electron microscope, in keV

126
(33)
A magic number

146
(29)
Number of neutrons in uranium-238

300
(27)
Years it takes for the first cesium atomic clock to lose one second

400
(54)
The Chernobyl accident released this times more radiation than
the Hiroshima bomb


400-700
(18)
Wavelength of visible light, in nanometers

438
(52)
Number of operational power generation reactors as of 2015

450
(57)
Order of magnitude with which first hydrogen bomb was more
powerful than the Nagasaki bomb

500
(27, 59, 62)
Average velocity of molecules in room temperature gas in m/s;
power output of the NIF, in trillions of watts; millions of dollars
allocated to the Manhattan Project in 1942

 (27)
632.8
Wavelength of HeNe laser light, in nanometers

653
(56)
Tons of helium produced by the Sun every second

 (14)
656.3
Wavelength of the red line in the hydrogen spectrum in
nanometers

657
(56)
Tons of hydrogen processed by the sun every second

 (29)
931.49
Mass of one unified mass unit, in MeV/c2

 (30)
938.28
Mass of one proton in MeV

 (30)
939.57
Mass of one neutron in MeV

 (10, 59)
1,000
Kelvin at which objects release radiation in the infrared band;
when firing a laser pulse, the NIF consumes this much times more
power than the entire United States

 (7)
1,800
Order of magnitude with which hydrogen atom is more massive
than a cathode ray particle

 (62)
1,200
Tons of imported uranium stored at Staten Island in the
Manhattan Project`

 (40)
1,600
Half-life of radium-226, in years

 (67)
21,000
Energy release of Fat Man, in tons of TNT

 (62)
2,403
Deaths at Pearl Harbor

 (38)
3,000
Artificial radioactive isotopes created in reactors and particle
accelerators

 (44)
5,730
Half-life of carbon-14, in years

 (61)
6,000
Initial value of uranium oxide and graphite suggested by the
Advisory Committee on Uranium, in dollars

 (58)
10,000
Energy of 1 gram of deuterium, in liters of gasoline

 (67)
15,000
Energy release of Little Boy, in tons TNT

 (50, 66)
20,000
Tons of TNT with energy equivalent to 1 ton of uranium or the
Trinity bomb

 (52)
24,000
Half-life of plutonium-239, in years

104 (49)
4.4 ×
Energy density of gasoline, in J / g

 (44)
50,000
Maximum age of an item for carbon dating, in years

 (67)
74,000
Immediate deaths resulting from the Fat Man bombing

 (30, 61)
100,000
Order of magnitude that the atom is larger than the nucleus;
initial value of uranium oxide and graphite suggested by the
Advisory Committee on Uranium, in 2015 dollars

 (67)
130,000
Employees of the Manhattan Project at the end of the war

 (67)
140,000
Immediate deaths resulting from the Little Boy bombing

 (54)
500,000
Maximum energy of a fission bomb, in tons TNT

107 
(55)
Temperature at which nuclear fusion occurs, in Kelvin

5 ×
107 (44)
Minimum half-life of a primordial isotope for it to be detectable

108 
(59)
Temperature reached by the deuterium pellet in the NIF, in Kelvin

200
million (59)
Maximum temperature reached by the TFTR, in Kelvin

300
million (27)
Years taken for modern cesium atomic clocks to lose one second

109 (44)
4.5 ×
Half-life of uranium-238, in years; age of the Earth, in years


4.6 billion
(40)
Age of the Solar System, in years


9,192,631,770
(27)
Oscillations of cesium-137 per second

1010 (39)
3.7 ×
1 Curie in decays per second

 1010 (49)
8.2 ×
Energy density of uranium-235, in J/g

1011(43)
Flux of neutrinos on Earth's surface, neutrinos per sq cm/s

1014s/cm3 (58)
Minimum value of Lawson's criterion for deuterium-tritium fusion

1016s/cm3 (58)
Minimum value of Lawson's criterion for deuterium-deuterium
fusion
Places


Alamogordo
(65)
New Mexico location of the Trinity test

 Greece (5)
Ancient
One of the first cultures to theorize atoms; home to Democritus,
Leucippus, Plato, Aristotle

 Idaho (52)
Arco,
Site of the first nuclear reactor which generated electricity


Australia
(57)
Home of Mark Oliphant

 (19)
Austria
Home of Erwin Schrödinger


California
(59)
Location of Lawrence Livermore National Laboratory

 (51, 62)
Canada
Country which uses many heavy-water reactors; provided uranium
for the Manhattan Project

 (46)
CERN
Location of the Large Hadron Collider

 (59)
China
ITER member state


Colorado
(62)
Site of American uranium mines for the Manhattan project


Denmark
(14)
Home of Niels Bohr

 Colorado (43)
Denver,
City in the United States with high cosmic radiation exposure due
to its high altitude


England
(6, 31, 46, 48, 56, 59,
62)
Home of John Dalton, James Chadwick, John Cockcroft, Arthur
Eddington; site of the Joint European Torus; estimated the critical
mass of uranium-235 to be 10 kg

 (6, 17, 34, 52, 59)
France
Home of Antoine Lavoisier, Joseph Proust, Louis de Broglie, Marie
Curie, Pierre Curie, Henri Becquerel; generates 75% of its energy
with nuclear power; site of ITER


Fukushima
Daiichi (41)
Experienced a major nuclear accident in 2011


Germany
(11, 34, 48, 61)
Home of Albert Einstein, Max Planck, Wilhelm Roentgen, Otto
Hahn, Fritz Strassman; home of the Nazi Party; led by Adolf Hitler


Hiroshima
(67)
Japanese city targeted by Little Boy


Hungary
(48)
Home of Leo Szilard

(5, 59)
India
Early culture that theorized atoms; home to Kanada; ITER member

 (46)
Ireland
Home of Ernest Walton

Italy(61)
Country with a fascist government; ruled by Benito Mussolini

 (41)
Japan
Location of Fukushima Daiichi nuclear power plant

 (59)
Japan
ITER member state


Knoxville
(64)
Populated city located close to the Oak Ridge site

 (67)
Kokura
Japanese manufacturing center; considered for nuclear bombing

 (59)
Korea
ITER member state

 (67)
Kyoto
Former capital of Japan and center of industry; considered for
targeting but rejected due to its historical significance


Nagasaki
(67)
Japanese seaport and center of industry; targeted instead of
Kyoto by the Fat Man bomb


Netherlands
(9)
Home of Christiaan Huygens

OakRidge (63)
City founded to house workers at the Clinton Engineer Works

Harbor (62)
Pearl
American naval base attacked by Japan on December 7, 1941


Pennsylvania
(52)
Site of the Three Mile Island accident

 (34, 61)
Poland
Homeland of Marie Curie; invaded by Germany in September
1939


Racquet
court (51)
Location on the University of Chicago campus where the first
nuclear reactor was constructed

 eastern Tennessee (63)
Rural
Site picked for the Oak Ridge nuclear plants

 (59)
Russia
ITER member state

 Fe (64)
Santa
Location of the P.O. Box of Los Alamos


Scotland
(9)
Home of James Clerk Maxwell

 Union (52)
Soviet
First country to connect a nuclear reactor to the power grid

 Island (62)
Staten
Storage site for imported uranium during the Manhattan project


Switzerland
(14)
Home of Johann Balmer

 States (13, 40, 52, 59)
United
Home of Arthur Compton, Donald Glaser, Willard Libby; generates
19.5% of its energy with nuclear power; world's largest producer
of nuclear power; ITER member state


Washington
(64)
State occupied by the Hanford Engineer Works


Yokohama
(67)
Japanese manufacturing center; possible target for nuclear bomb
Organizations


Advisory
Committee on
Uranium (61)
Committee formed by Roosevelt in response to Leo Szilard's
letter; provided recommendations for nuclear research

 Corps of Engineers (62,
Army
63)
Oversaw plant construction and bomb assembly in the production
phase of the Manhattan project


Asharite
School of Theology
(5)
Religious belief system formed by Islamic scholars studying Greek
and Indian atomism

 Energy Commission
Atomic
(68)
Organization which assumed control of the atomic program in
1947

Bell 
Labs (17)
Research center at which Clinton Davisson and Lester Germer
confirmed the de Broglie hypothesis


Carnegie
Foundation (62)
Organization of which Vannevar Bush was president


Catholic
Church (5)
Religious organization which initially opposed atomism

 (46)
CERN
Organization supporting the Large Hadron Collider

 Engineer Works (63)
Clinton
Organization established by the Army Corps of Engineers; later
became Oak Ridge National Laboratory


Department
of Energy (68)
Established in 1977 by Jimmy Carter; currently manages the
National Laboratories


Emergency
Committee of
Atomic Scientists (68)
Group founded by Albert Einstein in 1946 to promote peaceful
atomic applications

 Research and
Energy
Development Administration
(68)
Agency which partially replaced the Atomic Energy Commission in
1974


European
Union (59)
ITER member


Hanford
Engineer Works (64)
Housed the B Reactor, a plutonium generating reactor


International
Atomic Energy
Agency (69)
Founded by United Nations in 1957; promotes peaceful use of
nuclear materials; prevents the proliferation of nuclear weapons


Lawrence
Livermore National
Laboratory (59)
Site of the National Ignition Facility

Los 
Alamos (64)
Also known as Site Y; research area constructed to bring together
scientists working on the Manhattan Project

Los 
Alamos Ranch School
(64)
Site of what would become Site Y


National
Bureau of
Standards (61)
Organization directed by Lyman Briggs


National
Defense Research
Committee (62)
Proposed by Vannevar Bush to oversee development of the
atomic bomb


National
Institute of
Standards and Technology
(27)
Agency which regulates standards of measurements; defined the
second in terms of cesium 137's oscillating frequency


National
Laboratory system
(68)
System of research centers established by the Atomic Energy
Commission in the post-war era

NaziParty (61)
Political party which took control of Germany in 1933

NIST(27)
See National Institute of Standards and Technology

 Regulatory
Nuclear
Commission (68)
Agency that partially replaced the Atomic Energy Commission in
1974

OakRidge National
Laboratory (68)
Laboratory that grew out of the Clinton Engineer Works


Princeton
(59)
Site of the Tokamak Fusion Test Reactor

 Y (63)
Project
Weapons development laboratory of the Manhattan Project; led
by J. Robert Oppenheimer

S-1 
Committee (62)
Subcommittee of the NRDC investigating uranium enrichment;
included Ernest O. Lawrence


Scientific
Advisory Panel (67)
Rejected a public demonstration of the nuclear bomb

Site
Y (64)
See Los Alamos


Stanford
(27)
Research university which supercooled rubidium to 50 trillionths
of a Kelvin in 2015

 Nations (69)
United
Founder of the International Atomic Energy Agency

 States Army (62)
United
Directed the construction of the atomic bomb


University
of California,
Berkeley (62, 64)
University of Ernest O. Lawrence, J. Robert Oppenheimer, Hans
Bethe, Edward Teller


University
of Chicago (51)
School which hosted the world's first nuclear reactor


US Food
and Drug
Administration (43)
Department overseeing food irradiation
People

 Hitler (61)
Adolf
Chancellor of Germany; leader of the Nazi Party

 Einstein (13, 18, 25)
Albert
Proposed quantization of light energy (1905); won 1921 Nobel
Prize for explaining the photoelectric effect; expressed doubts
about quantum theory to Max Born; theorized a fourth state of
matter with integer spin particles (1924)

Weinberg (68)
Alvin
Director of Oak Ridge National Laboratory; coined the term "Big
Science" to describe the National Laboratory system

 Lavoisier (6)
Antoine
Late 1700s French chemist; identified and named hydrogen and
oxygen; theorized the law of conservation of matter


Aristotle
(5)
Third century BCE Greek philosopher; disagreed with atomism;
argued that matter is infinitely divisible

 Compton (13, 62)
Arthur
American physicist; noted X-ray scattering in 1923, suggesting the
existence of the photon; asked J. Robert Oppenheimer to perform
neutron calculations for the uranium chain reaction; suggested
Oppenheimer as the director of Project Y

 Eddington (56)
Arthur
English physicist; proposed stars produce energy through
hydrogen fusion

CarlWieman (25)
Created a Bose-Einstein condensate using laser cooling in 1995


Christiaan
Huygens (9)
Dutch physicist; contemporary of Newton’s; envisioned light as a
wave

 Davisson (17)
Clinton
Researcher at Bell Labs; experimentally confirmed the de Broglie
hypothesis by firing electrons at crystalline nickel


Democritus
(5)
Fifth century BCE; early Greek philosopher; suggested that matter
is composed of indestructible, indivisible particles

 Mendeleev (6, 7)
Dmitri
Nineteenth century chemist; created periodic table based on first
64 elements; predicted the existence of gallium

 Glaser (40)
Donald
Invented the bubble chamber in 1952

 D. Eisenhower (69)
Dwight
President of the United States; in 1953 delivered "Atoms for
Peace" speech to the United Nations

 Teller (57, 62)
Edward
Hungarian-American physicist; conceived of and designed the first
hydrogen bomb; Berkeley "luminary" who worked with
Oppenheimer on neutron calculations for the atomic bomb

 Segre (62, 65)
Emilio
Worked with Oppenheimer on neutron calculations; found that
products of X-10 reactor had too much plutonium-240 for a guntype bomb

 Fermi (30, 37, 48, 51,
Enrico
61)
Italian physicist after whom unit of nucleic radius is named; named
the neutrino; synthesized neptunium and plutonium; constructed
the first nuclear reactor at the University of Chicago in 1942; fled
to the United States during this period

Eric 
Cornell (25)
Created a Bose-Einstein condensate using laser cooling in 1995

 Marsden (7)
Ernest
Assistant to Ernest Rutherford in the gold foil experiment

 O. Lawrence (62)
Ernest
Director of Radiation Laboratory at Berkeley; inventor of cyclotron

 Rutherford (7, 30, 35,
Ernest
57)
Performed 1911 gold foil experiment; discovered the nucleus;
theorized the neutron in 1920; proposed planetary atomic model;
proposed in 1900 that nuclear transformations release radiation;
experimentally demonstrated nuclear fusion in 1934

 Walton (46)
Ernest
Irish physicist; in 1932, induced the first artificial nuclear reaction
with lithium-7

 Schrödinger (19, 22)
Erwin
Austrian physicist; created equation describing behavior of matter
waves; described quantum behavior via scenario of cat in a box

 Rabinowitch (68)
Eugene
Manhattan Project scientist; founded Bulletin of the Atomic
Scientists

 Wigner (33)
Eugene
Proposed shell model for nucleons with Maria Goeppert Mayer

FelixBloch (62)
Worked with J. Robert Oppenheimer on neutron calculations

 D. Roosevelt (62)
Franklin
President of the United States; approved initial research into an
atomic weapon; approved the NDRC


Frederic
Curie (37)
Husband to Irene Joliot-Curie; in 1934, demonstrated induced
radioactivity by generating radioactive phosphorous; won the
1935 Nobel Prize in Chemistry


Frederick
Soddy (35)
In 1900, concluded that nuclear transformations release radiation
with Ernest Rutherford

FritzStrassman (48)
German physicist; in 1938, discovered that bombarding uranium
nuclei with neutrons produced fission products with half
uranium’s mass

 Gamow (23)
George
In 1940, wrote Mr. Tompkins in Wonderland

 Hertz (16)
Gustav
In 1914, confirmed Bohr's model of the atom by firing electrons
through mercury gas in a vacuum

Bethe (57, 62)
Hans
In 1939, proposed the proton-proton chain and CNO cycle; won
the 1967 Nobel Prize; "luminary" who worked with Oppenheimer
on neutron calculations

Geiger (7, 40)
Hans
Assistant to Ernest Rutherford; performed the gold foil experiment
in 1911; recorded the results of the gold foil experiment in a dark
room; developed a radiation detector which uses a low-pressure
tube of inert gas

 Truman (66)
Harry
Vice President to President Franklin D. Roosevelt; became
president in 1945 after Roosevelt died in office


Heinrich
Hertz (12)
In 1887 discovered the photoelectric effect

 Becquerel (34)
Henri
French physicist; first observed spontaneous radiation emission

 Wallace (62)
Henry
Vice President to President Franklin D. Roosevelt

Joliot-Curie (37)
Irene
Daughter of Marie Curie; in 1934, demonstrated induced
radioactivity by generating radioactive phosphorous; won the
1935 Nobel Prize in Chemistry

Newton (6, 9)
Isaac
1700s - 1800s; advocated for the corpuscular theory in Opticks


J. Robert
Oppenheimer (62,
63)
Researcher at the University of California, Berkeley; performed
neutron chain calculations for the atomic bomb; assembled a
team of "luminaries" to study neutron calculations; affiliated with
Communism through family members; became head of Project Y

J.D. 
Lawson (58)
Proposed criteria for nuclear fusion to occur


J.J. Thomson
(7, 12)
Measured the mass of a cathode ray particle in 1897; discovered
the electron; proposed the plum pudding model of the atom;
determined that sparks produced by the photoelectric effect are
actually electrons

 Chadwick (31, 48)
James
English physicist; in 1931 performed experiments with paraffin to
confirm the existence of the neutron

 Clerk Maxwell (9)
James
Scottish physicist; devised the unified theory of electromagnetism
in the late 19th century; described light as oscillating electric and
magnetic fields

 Franck (16)
James
In 1914, confirmed Bohr's model of the atom by firing electrons
through mercury gas in a vacuum

 Carter (68)
Jimmy
President of the United States; established Department of Energy

 Balmer (14)
Johann
Swiss mathematical physicist; in 1885 derives a mathematical
relation between the lines in hydrogen's spectrum

JohnCockcroft (46)
British physicist; in 1932, induced the first artificial nuclear reaction
with lithium-7

JohnDalton (6)
English chemist; combined discoveries of Lavoisier and Proust;
formulated the first atomic theory in A New System of Chemical
Philosophy; catalogued atomic weights

JohnDonne (65)
English poet; inspired the name of the Trinity test

JohnVan Vleck (62)
Worked with J. Robert Oppenheimer on neutron calculations

Johnvon Neumann (65)
Mathematician; in September 1943, proposed an implosion type
weapon design

JohnWheeler (48)
Colleague of Neils Bohr

 Proust (6)
Joseph
French chemist; realized that elements react in fixed proportions

 (5)
Kanada
Fifth century BCE Hindu philosopher; suggested that matter
contains indestructible, indivisible particles

Leo 
Szilard (48, 61, 66)
Hungarian physicist; in 1933, hypothesized that a nuclear chain
reaction could become self-sustaining; fled to the United States; in
1939 wrote a letter under Einstein's name recommending the
United States research nuclear weapons; petitioned for a public
demonstration of the nuclear bomb

 R. Groves (63)
Leslie
Army Corps of Engineers General; director of the Manhattan
Project from September 1942; appointed Oppenheimer as its lead

 Germer (17)
Lester
Researcher at Bell Labs who experimentally confirmed the de
Broglie hypothesis by firing electrons at crystalline nickel


Leucippus
(5)
Fifth century BCE Greek philosopher; suggested that matter is
composed of indestructible, indivisible particles

 Straus (68)
Lewis
Predicted that nuclear power would make electricity free; AEC
commissioner; sought to discredit Oppenheimer for opposing the
hydrogen bomb

Lise
Meitner (48)
Collaborated with Otto Hahn and Fritz Strassman

 de Broglie (17)
Louis
French physicist; in 1924, suggested a relationship between a
particle's momentum and wavelength

 Goeppert Mayer (33)
Maria
In 1949, proposed a shell model for nucleons with Eugene Wigner

 Curie (34)
Marie
French-Polish physicist; discovered polonium with husband; won
1903 and 1911 Nobel Prizes; died from radiation exposure in 1934

 Oliphant (57, 62)
Mark
Australian physicist; in 1934 experimentally demonstrated nuclear
fusion; represented the British atomic team in United States

MaxBorn (18, 20)
Received a letter from Albert Einstein on his skepticism about
quantum theory; in 1926, proposed that the square of a wave
function is the particle's probability density

MaxPlanck (11)
German physicist; proposed the quantization of atomic energy

 Faraday (7)
Michael
Discovered that generating an electric voltage across a cathode
ray tube caused the positive end to glow

Bohr (14, 16, 48)
Niels
Danish physicist; modified the atomic model to explain
quantization of energy; postulated the correspondence principle

OttoHahn (48)
German physicist; discovered that bombarding uranium nuclei
with neutrons produced fission products half as heavy as uranium

OttoRobert Frisch (48)
Collaborated with Otto Hahn and Fritz Strassman; coined "fission"

PaulDirac (24)
In 1928, derived a relativistic form of the Schrödinger equation,
incorporating the spin quantum number into quantum mechanics

 Lenard (12)
Phillip
In 1900, noticed several contradictions between the photoelectric
effect and classical physics

 Curie (34)
Pierre
French physicist; discovered polonium with his wife; researched
radioactivity

 Gassendi (5)
Pierre
Renaissance-era priest; reconciled atomism with Catholic beliefs

(5)
Plato
Greek philosopher; viewed matter as consisting of four basic
elements; assigned geometric shapes to types of matter

Descartes (6)
Rene
Philosopher who debated Pierre Gassendi during the Renaissance

 Boyle (6)
Robert
Eighteenth century founder of modern chemistry; proposed
corpuscular theory

 Serber (62)
Robert
Worked with J. Robert Oppenheimer on neutron calculations


Satyendra
Bose (25)
Theorized fourth state of matter with integer spin particles

SethNeddermeyer (65)
Physicist; conducted theoretical work which led to the design of
an implosion type weapon


Stanislaw
Ulam (57)
Performed calculations for Edward Teller, contributing to the
design of the hydrogen bomb

 Young (9)
Thomas
Noticed double-slit interference in 1803;


Vannevar
Bush (62)
American science administrator; president of Carnegie
Foundation; proposed and first chair of the NDRC


Wilhelm
Roentgen (34)
German physicist; discovered X-rays in 1895; won 1901 Nobel
Prize in Physics

 Libby (44)
Willard
American physical chemist; in the 1940s developed carbon dating;
won the 1960 Nobel Prize in Chemistry

 Lawrence (68)
William
New York Times journalist who coined the term "Atomic Age"


Wolfgang
Pauli (24, 37)
In 1925, suggested that no two electrons in an atom can share all
four quantum numbers; in 1930, theorized the neutrino
𝑅 = 𝑅0 𝑒 −𝜆𝑡
𝑁 = 𝑁0 𝑒 −𝜆𝑡
𝛥𝑁 = −𝜆𝑁Δ𝑡
𝑡ℎ =
ln 2
𝜆
𝑅=
𝑅0 =
𝜆=
𝑁=
𝑁0
𝑡=
𝑡ℎ =
𝜆=
ℎ
𝜆=
𝑝
ℎ = 6.626 × 10−34
𝑚2
𝑘𝑔⋅𝑠
=
𝑝=
1
1
1
= 𝑅𝐻 ( 2 − 2 )
𝜆
𝑚
𝑛
ℎ
Δ𝑥Δ𝑝 ≥
2𝜋
𝜆=
𝑅𝐻 = 1.097 × 107 𝑚−1
𝑚=
𝑛=
Δ𝑥 =
Δ𝑝 =
ℎ = 6.626 × 10−34
𝑚2
𝑘𝑔⋅𝑠
=
𝐸=
𝑛=
𝐸 = 𝑛ℎ𝑓
ℎ = 6.626 × 10−34
𝑚2
𝑘𝑔⋅𝑠
=
𝑓=
𝐸 = 𝑚𝑐
2
𝐸=
𝑚=
𝑐 = 3 × 108
𝐸𝑛 =
−13.6 𝑒𝑉
𝑛2
𝑠
=
𝐸𝑛 =
𝑛=
2
𝑟𝑏 =
𝑛=
𝑎0 = 0.0529 𝑛𝑚 =
1
𝑟0 𝐴3
𝑟=
𝑟0 = 1.2 × 10−15 𝑚
𝐴=
𝑟𝑏 = 𝑛 𝑎0
𝑟=
𝑚
𝑛=
𝜏=
𝑛𝜏 > 𝑘
𝑘 = 1014
𝑠
𝑐𝑚3
𝑘 = 1016
𝑠
𝑐𝑚3
𝐴
𝑍𝑋
𝐴
𝑍𝑋
𝐴
𝑍𝑋
𝐴−4
𝑍−2𝑌
→
+ 42𝐻𝑒
→
𝐴
𝑍+1𝑌
1
0𝑛
→ 11𝑝 + 𝑒 −
→
𝐴
𝑍−1𝑌
238
92𝑈
→
+ 𝑒 − + 𝑣̅
+ 𝑒+ + 𝑣
234
90𝑇ℎ
14
7𝑁
+ 42𝐻𝑒
14
6𝐶
→
7
4𝐵𝑒
+ 𝑒 + → 73𝐿𝑖 + 𝑣
14 ∗
6𝐶
4
2𝐻𝑒
14
6𝐶
→
30
14𝑆𝑖
+ 147𝑁 →
+𝛾
30
15𝑃
+ 27
13𝐴𝑙 →
30
15𝑃
4
2𝐻𝑒
→
+ 𝑒 − + 𝑣̅
+ 10𝑛
+ 𝑒+
17
8𝑂
+ 11𝐻
1
1𝑝
+ 73𝐿𝑖 → 2 42𝐻𝑒
2
1𝐻
+ 73𝐿𝑖 → 2 42𝐻𝑒
1
0𝑛
+ 235
92𝑈 →
140
54𝑋𝑒
94
+ 38
𝑆𝑟 + 2 10𝑛
1
0𝑛
+ 235
92𝑈 →
141
56𝐵𝑎
92
+ 36
𝐾𝑟 + 3 10𝑛
2
1𝐻
+ 31𝐻 → 42𝐻𝑒 + 10𝑛 + 17.59 𝑀𝑒𝑉
2 21𝐻 → 32𝐻𝑒 + 10𝑛 + 3.27 𝑀𝑒𝑉
2 21𝐻 → 31𝐻 + 11𝐻 + 4.03 𝑀𝑒𝑉
2 11𝐻 → 21𝐻 + 𝑒 + + 𝑣 + 0.42 𝑀𝑒𝑉
1
1𝐻
+ 21𝐻 → 32𝐻𝑒 + 𝛾 + 5.49 𝑀𝑒𝑉
2 32𝐻𝑒 → 42𝐻𝑒 + 2 11𝐻 + 12.86 𝑀𝑒𝑉
This year’s science practice test places slightly more emphasis on understandings of the atomic model
over nucleic reactions, with section I having 34% of questions against 26% and 24% for sections II
(atomic nucleus and radioactivity) and section III (nuclear fission and fusion) respectively.
Section I questions focus heavily on models of the atom, both classical and quantum; little appears
on foundational findings leading to the quantum model such as spectral lines, the de Broglie
hypothesis, wave-particle duality, and Schrödinger’s equation.
Section II also focuses on atomic structure, specifically of the nucleus. Few questions address gamma
decay, induced radioactivity, and radioactivity detection and effects – though this last topic offers
great recall questions, so know this material well. Section III almost completely skips over Q values
and the discovery of fission, while section IV omits the detonation mechanisms and Trinity Test
portions, both of which will likely appear on later tests.
As might be expected, section IV questions are much more factual. Those from other sections do
require some lateral thinking and analysis, for example question 13 on analogies to Planck’s
quantized energy states. The correct answer, B, can be identified quickly once you observe that only
books increase stepwise (you cannot add half a book to a bookcase). Question 24 requires you to
connect material from different sections of the guide; cathode rays stand out as not being part of
the typical electromagnetic spectrum but rather a type of emission.
No math needed for this test, but know the elements and reactions: for example, question 26 on the
uranium-238 decay series points to an important equation, as does question 37 on the three decay
chains’ products. The closest you will be to calculating anything is on question 33. Recall that doubly
magic implies both neutron and proton numbers are magic; i.e. their sum (A) is twice the magnitude
of a magic number. In this case, 20 x 2 = 40, option B. The more tricky questions that require you to
pay close attention are the substantial number on standards and notation (11, 41, 45, 46) as well as
chronology and “firsts” (2, 12, 17, 47, 48, 50). Quite a few questions came in the form of “who
discovered X?” or “what did the discovery of X enable?”, so pay attention where it appears in the
guide.
Lastly, two questions that may need some clarification: the phrasing of question 18 leaves it unclear
what it is asking about, and the distracters vary between criteria for the process to occur (A, C) and a
description of the process (B, D, E). The answer, B, is relatively straightforward – in this case, no hidden
meanings involved; just go with the choice that fits most closely with the term provided. For question
29, students with more general knowledge of the topic may know that though the guide does not
explicitly state so, the uncertainty principle is generalizable to other quantum properties that form
correlate pairs. The most well-known, and only one the guide discusses, is position and momentum.