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1895 Wilhelm Roentgen Using a Cathode Ray Tube (CRT) he
observed that nearby chemicals glowed with fluorescent
properties. Further experiments found penetrating rays coming
from the CRT that were not deflected by a magnetic field. He
named them "X-rays".
1896 Henri Becquerel While studying the effect of x-rays on
photographic film, he discovered some chemicals spontaneously
decompose and give off high penetrating rays. He discovered
“radioactivity”.
1898 Ernest Rutherford Studied radiations emitted from
uranium and thorium and named them alpha and beta.
1898 Marie Curie Studied uranium and thorium and called their
spontaneous decay process "radioactivity". She and her
husband Pierre also discovered the radioactive elements
polonium and radium.
1905 Albert Einstein Published the famous equation E=mc2
1911 Ernest Rutherford Using alpha particles as atomic
bullets, probed the atoms in a piece of thin (0.00006 cm) gold
foil. He established that the nucleus was: very dense, very
small and positively charged.
1938 Enrico Fermi Conducted the first controlled chain reaction
releasing energy from the atoms nucleus. Received the Nobel
prize in physics for producing new radioactive elements via
neutron irradiation, and work with nuclear reactions.
1941 – 51 Glenn Seaborg Synthesized 6 transuranium
elements and suggested a change in the layout of the periodic
table. Pioneer of the modern periodic table.
July 16, 1945, the first atomic bomb was tested in an isolated
area of the New Mexico desert. 6kg of plutonium
detonated. Shortly thereafter we decided to end WWII.
Nuclear Radiation is a form of ionizing radiation that results from
changes within an atoms nucleus. Atoms with unstable nuclei can
spontaneously change their identity. All elements with atomic
numbers greater than 83 (Bismuth) are radioactive.
Nonionizing Radiation (low energy UV – Radio): Low energy
radiation that causes matter to vibrate (infrared) or move electrons to
higher energy levels (visible).
Ionizing Radiation (high energy UV, X-Rays, Gamma Rays, Cosmic
Rays): High energy radiation that carries more potential harm and
can cause serious damage to cells.
Ernest Rutherford publishes his atomic theory
describing the atom as having a central positive nucleus
surrounded by negative orbiting electrons. This model
suggested that most of the mass of the atom was
contained in the small nucleus, and that the rest of the
atom was mostly empty space. http://micro.magnet.fsu.edu/electromag/java/rutherford/
The nucleus is composed of nucleons (protons & neutrons)
The nucleons have the same identical mass of about 1.7 x 10-24
grams. The mass for a proton & neutron is about 2000 times more
than the mass of an electron.
All atoms of an element have the same number of protons but all
atoms of one element do not necessarily have the same number of
neutrons.
Atoms of the same element but having a different number of neutrons
is called an isotope. (Iso- meaning “same”, tope- meaning “place”)
Isotopes are distinguished by their different mass numbers.
Remember the atomic mass is the total number of nucleons in an
atom. (Protons + Neutrons)
Isotopes are written with the name followed by the mass number.
Example: Carbon – 12, Carbon – 13, Carbon – 14,
Isotopes are atoms of the same element having different
masses due to varying numbers of neutrons.
Isotope
Protons Electrons
Neutrons
Hydrogen–1
(protium)
1
1
0
Hydrogen-2
(deuterium)
1
1
1
Hydrogen-3
(tritium)
1
1
2
Nucleus
Elements with atomic numbers greater than 83 (Bismuth) are naturally
radioactive isotopes.
Modern technology has made it possible to create a radioactive isotope
of any element.
Types of Radiation
Alpha particle ()
 helium nucleus
4
2
Beta particle (-)
 electron
0
-1
Positron (+)
 positron
0
1
e
Gamma ()
 high-energy photon
He
e
2+
paper
1lead
1+
0
0

concrete
Alpha, Beta, Gamma Rays
Lead block
 rays
(+)
(negative charge)
Aligning
slot
(no charge)
Radioactive
substance
(-)
Electrically charged
plates
 rays
 rays
(positive charge)
Photographic
plate
(detecting screen)
Types of Radiation
• Alpha (ά) – a positively
charged helium isotope
•Beta (β) – an electron
•Gamma (γ) – pure energy;
called a ray rather than a
particle
4
2
He
0
1
0
0
e

Other Nuclear Particles
• Neutron
•Positron – a positive electron
•Proton – usually referred to
as hydrogen-1
1
0
n
0
1
1
1
e
H
Natural or Background Radiation
• We are all being exposed daily to a variety of radiation
• We receive about 100 mREM/year from background
– The average non-occupational worker receives about 200
mREM/year of chronic radiation exposure
• Present at all times as a result of radiation naturally present in
the environment
– Cosmic rays
– Uranium, thorium and radon in soil
– Building materials
• We receive an additional 100 mREM/year from
– Medical and dental x-rays
– Smoke detectors
– Dials on watches, etc.
– Cell phones, TV’s,
• Differs depending on geographical location
Radiation Dosages
Dose (Amount + Energy)
rad = radiation absorbed dose – absorbed
radiation energy per kg of material
Gray (Gy) SI Base Unit for absorbed dosage
= 100 rad
rem = radiation for roentgen equivalent man
Sievert (Sv) SI Base Unit for radiation equivalent
man = 100 rem
(1 Gy = 100 rad, 1 Sv = 100 rem)
Everyday Radiation Exposure
Factors to Reduce Exposure
• Time
• Distance
• Shielding
Time
• If you decrease the time exposed
to a given isotope you will
decrease the dose of that
exposure
Distance
• Inverse Square Law
–If you double the distance
between you and a
radioactive source you
reduce the amount of
exposure by ¼
Shielding
(Barrier between you and the source)
• Type needed depends on type
of radiation produced
– Alpha
• Air
• Paper
• Clothes
– Beta
• Metal
• Wood
• Plexiglass
– Gamma
• Concrete
• Lead
Dosages Required for Certain Immediate
Effects
• 0-100 REM’s
– Survival certain
– No obvious symptoms
– Maybe some clinical signs if lab tests are done
• 100-200 REM’s
– Survival probable
– Begins signs of light radiation sickness
• Nausea
• Vomiting
• Listlessness
• 200-700 REM’s
– Survival questionable. Some will survive, some won’t.
– Severe radiation sickness
– Radiation burns
• Over 700 REM’s
– Survival impossible
Radiation Measurement
A Geiger counter
• detects beta and gamma radiation.
• uses ions produced by radiation to
create an electrical current.
Geiger Counter
Ionization of fill gas
takes place along
track of radiation
(-)
(+)
Speaker gives
“click” for
each particle
Metal tube
(negatively
charged)
Window
+
e-
e+
+
+ ee-
Ionizing
radiation
path
Atoms or molecules
of fill gas
Central wire electrode
(positively charged)
Free e- are attracted to
(+) electrode, completing
the circuit and generating
a current. The Geiger
counter then translates
the current reading into a
measure of radioactivity.
Most of the isotopes which occur naturally are stable.
A few naturally occurring isotopes and all of the manmade isotopes are unstable.
Unstable isotopes can become stable by releasing
different types of particles.
This process is called radioactive decay and the
elements which undergo this process are called
radioisotopes/radionuclides.
Radioactive Decay
Radioactive decay results in the emission or capture
of either:
• an alpha particle (),
• a beta particle (),
• a gamma ray (),
• a postitron ray (),
• a proton (p+),
• a neutron (no).
A
X
Z
A (Mass Number) = number of protons + number of neutrons
Z (Atomic Number) = number of protons
A – Z = number of neutrons
X
= Element Symbol
Number of neutrons = Mass Number – Atomic Number
The 238U Decay Series
Alpha Decay
Alpha Decay (): The
loss of an alpha
particle which is a
helium nucleus
4
2
He
U  He 
238
92
4
2
244
94
Pu  He 
unstable atom
4
2
alpha particle
234
90
Th
240
92
U
more stable atom
Alpha decay is limited to heavy, radioactive
nuclei. Numbers must balance on both sides.
Alpha Decay
alpha particle
radioactive isotope
neutron
proton
U 
 He
238
92
4
2
2

234
90
Th
Alpha Decay
A
A-4
4
226
222
4
X
Z
Ra
88
Y
+
Z-2
Rn
+
86
He
2
He
2
Numbers must balance on both sides
Alpha Decay
222
Rn
86
222
Rn
86
A
4
Y
He
+
Z
2
218
Po
+
84
4
He
2
Alpha Decay
230
Th
90
230
Th
90
A
4
226
4
Y
He
+
Z
2
Ra
He
+
88
2
Alpha Decay
A
214
4
218
214
4
X
Z
Po
84
Pb
He
+
82
2
Pb
He
+
82
2
Beta Decay
Beta production ():
A beta particle is an
electron ejected from
the nucleus
0
1
Th 
234
91
Pu 
244
95
234
90
244
94
unstable atom
e
Pa 
0
1
Am 
0
1
e
e
More stable atom Beta particle
Beta emission converts a neutron (no charge) to a proton
(positive charge) due to the loss of an electron (negative
charge)
Beta Decay
Nuclear Decay
• Beta Emission
131
53
I
131
54
Xe  e
0
-1
electron
• Positron Emission
38
19
K  Ar  e
38
18
0
1
positron
Nuclear Decay
• Beta Capture
106
47
Ag  e 
0
-1
106
46
Pd
Electron capture
• Gamma Emission
– Usually follows other types of decay.
Positron Decay
Positron emission:
Positrons are the
anti-particle of the
electron
0
1
e
22
0
22
Na

e

Ne
11
1
10
unstable atom
positron
More stable atom
Positron emission converts a proton to a neutron
Beta Decay
A
X
Z
218
Po
84
A
Y
+
Z+1
218
At
+
85
0
e
-1
0
e
-1
Beta Decay
A
210
210
210
X
Z
Tl
81
Pb
+
82
Pb
+
82
0
e
-1
0
e
-1
Beta Decay
210
A
210
210
Bi
83
Bi
83
Y
+
Z
Po
+
84
0
e
-1
0
e
-1
Beta Decay
A
214
214
214
X
Z
Pb
82
Bi
+
83
Bi
+
83
0
e
-1
0
e
-1
Gamma Ray Production
Gamma ray production ():
•
238
4
234
0
U

He

Th

2

92
2
90
0
Gamma rays are high energy photons
produced in association with other forms of
decay.
Gamma rays are massless and do not, by
themselves, change the nucleus
Gamma Decay
When atoms decay by emitting  or  particles to
form a new atom, the nuclei of the new atom
formed may still have too much energy to be
completely stable.
This excess energy is emitted as gamma rays
(gamma ray photons have energies of ~ 1 x 10-12 J).
Complete and balance the following reactions
a.
7
3
Li
+
1
1
H
b.
3
1
H
+
2
1
H
c.
14
6
C
d.
26
12
Mg
14
7
+
1
0
4
2
He + ________
1
0
n + ________
N + ________
n
0
+1
e + ________
For (e): Polonium – 214 goes through beta particle decay
e.
214
Po
84
+
0
e
-1
________
Half-Life
• HALF-LIFE is the time that it takes for
1/2 a sample to decompose.
• The rate of a nuclear transformation
depends only on the “reactant”
concentration.
Kinetics of Radioactive Decay
For each duration (half-life), one half of the
substance decomposes.
For example: Ra-234 has a half-life of 3.6
days
If you start with 50 grams of Ra-234
After 3.6 days > 25 grams
After 7.2 days > 12.5 grams
After 10.8 days > 6.25 grams
Half-life
• The half-life (t1/2) of a radioactive nuclide is the time
required for one-half the nuclei in a sample of the
nuclide to decay.
For 1000 mg of
I-131 to decay …
… to 500 mg
takes 8 days.
It takes another 8
days for 500 mg to
decay to 250 mg …
… and 8 more days
for 250 mg to decay
to 125 mg.
Half-Life Is Characteristic of
the Radioisotope
Radiocarbon Dating
Radioactive C-14 is formed in the upper
atmosphere by nuclear reactions initiated by
neutrons in cosmic radiation
14N + 1 n ---> 14C + 1H
o
The C-14 is oxidized to CO2, which circulates
through the biosphere.
When a plant dies, the C-14 is not replenished.
But the C-14 continues to decay with t1/2 =
5730 years.
Activity of a sample can be used to date the
sample.
Learning Check!
The half life of I-123 is 13 hr. How much of
a 64 mg sample of I-123 is left after 39
hours?
Nuclear Medicine
• Radioisotope Tracers
– absorbed by specific organs and used to
diagnose diseases
• Radiation Treatment
– larger doses are used
to kill cancerous cells
in targeted organs
– internal or external
radiation source
Radiation treatment using
-rays from cobalt-60.
Radioisotopes in Medicine
•
1 out of every 3 hospital patients will undergo a nuclear
medicine procedure
•
24Na,
•
131I,
t½ = 14.8 hr,  emitter, thyroid gland activity
•
123I,
t½ = 13.3 hr, ray emitter, brain imaging
•
18F,
t½ = 1.8 hr,  emitter, positron emission tomography
•
99mTc,
t½ = 14.8 hr,  emitter, blood-flow tracer
t½ = 6 hr, ray emitter, imaging agent, identifies
tumors
Brain images
with 123I-labeled
compound
23.7
Food Irradiation
•Food can be irradiated with  rays from
60Co or 137Cs.
•Irradiated milk has a shelf life of 3 mo.
without refrigeration.
•USDA has approved irradiation of meats
and eggs.
Transmutations
• The changing of one element to another is
called transmutation
• This occurs whenever there is an alpha
decay or a beta decay
• Remember, that for a gamma decay, the
nucleus just changes internal energy
levels, but doesn’t change the identity of
nucleons
Synthetic Elements
• Transuranium Elements
– elements with atomic #s above 92
– synthetically produced in nuclear reactors
and accelerators
– most decay very rapidly
238
92
U
4
2
He 
242
94
Pu
Energy and Mass
Nuclear changes occur with small but
measurable losses of mass. The lost mass is
called the mass defect, and is converted to
energy according to Einstein’s equation:
E = mc2
m = mass defect
E = change in energy
c = speed of light (3.0
Because c2 is so large, even small
amounts of mass are converted to
enormous amount of energy.
x 108 m/s)
Nuclear Binding Energy
• The energy released in forming a nucleus
from its protons and neutrons is called the
nuclear binding energy.
• Although the energy is released, binding
energy is expressed as a positive quantity.
• Alternatively, nuclear binding energy is the
quantity of energy necessary to separate
a nucleus into individual protons and
neutrons.
Nuclear Binding Energy for
Helium
This small amount of
mass—the mass defect—
is equivalent to a huge
amount of energy.
The nucleus weighs less
than its nucleons. Some
mass was converted to
energy that holds the
nucleus together.
Fusion
• combining of two nuclei to form one
nucleus of larger mass
• thermonuclear reaction – requires temp of
40,000,000 K to sustain
• 1 g of fusion fuel =
20 tons of coal
• occurs naturally in
stars
2
1
H H
3
1
Fission
• splitting a nucleus into two or more
smaller nuclei
• 1 g of 235U = 3 tons of coal
235
92
U
http://www.visionlearning.com/library
/flash_viewer.php?oid=3602
Fission vs. Fusion
F
I
S
S
I
O
N
• 235U is limited
• danger of meltdown
• toxic waste
• thermal pollution
F
U
S
I
O
N
• fuel is abundant
• no danger of
meltdown
• no toxic waste
• not yet sustainable
Nuclear Weapons
• Atomic Bomb (Fission Bomb)
– chemical explosion is used to form a critical mass of 235U or
239Pu
– fission develops into an uncontrolled chain reaction
• Hydrogen Bomb
– chemical explosion  fission  fusion
– fusion increases the fission rate
– more powerful than the atomic bomb
http://www.visionlearning.com/library/flash_viewer.php?oid
=3602
Nuclear Fission & POWER
• Currently about 103
nuclear power plants
in the U.S. and about
435 worldwide.
• 17% of the world’s
energy comes from
nuclear.
Diagram of a nuclear power plant.
Nuclear Reactor
• Control rods can absorb
neutrons
• Control rods can be
lowered to absorb more
neutrons (slow reaction)
• Control rods can be
raised to absorb fewer
neutrons (increase
reaction)
Worldwide Nuclear Power Plants