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Radioactivity Unit Outline
1. Modern Quiz/Pasta Lab
2. Take up research assign, Decay equations, series
Blue book p. 940 P19, 20, 21, 22, 25, 27, 29
Red book p. 631 #13, p. 642 #1, 2, 3, 4
3. E = mc2, Geiger Counter demo
Blue book p. 939 Q1, 2, 3, 5, 8, 11*, 12*, 13*, 18, 19
(must do 11-13!!)
Red book p. 621 #5-8, p. 624 Concept Review,
p. 636 R2, 3, 5, 10, A1, 3, 5, P 4, 5, 6, 7
4. Fission and Fusion Assignment
Lesson #1
Introduction to Nuclear Physics
References: Chapters 30 and 31 in both books
Radiation and radioactivity are a part of our everyday lives. Radioactivity results from
instability within atomic nuclei, which causes them to decay, or split apart. This is
happening all the time, all around us. Flying on an airplane will actually give you a
similar dose of radiation to getting a medical X-ray done (within about 1000 times), since
you are closer to the sun and space while flying. Smoking cigarettes or being exposed to
a lot of second-hand smoke also gives you a significant dose of radiation. Radioactive
substances and radiation are routinely used for medical reasons (cobalt “bomb” for cancer
therapy or iodine treatment for thyroid problems). Different types of food are routinely
irradiated to stave off spoiling. Radiation sickness and other bad effects only usually
occur when people are exposed to unusually high doses of radiation, and/or over long
periods of time.
Glow-in-the-dark objects are made from radioactive substances. The nuclei in the
material are excited by light that falls on them (usually ultraviolet light). They reach a
higher energy metastable (“sort-of-stable”) state, from which they decay some time later.
During the decay, they emit photons of certain smaller frequencies, which we can then
see, and the atoms return to their lower-energy stable state. This makes them glow in the
dark.
There are 3 types of radiation that can be emitted by nuclei: alpha (), beta () and
gamma (). Each of these is associated with a certain type of nuclear decay. Nuclei decay
because (a) there is a lower energy state available to them; and/or (b) the strong nuclear
force can no longer hold all the protons and neutrons together (for large nuclei), and the
Coulomb (electrostatic) repulsion force of the protons takes over.
Alpha radiation
An  particle (wave) consists of two protons and two neutrons (a 4He nucleus). Note that
this is a positive particle. Generally alpha radiation has little energy although it is heavy.
Ex. Write the equation for the alpha decay of Uranium 238.
238
234
92 U  90Th  
parent 

daughter + alpha particle + energy
This process is called transmutation since one type of nucleus changes into another type
of nucleus. Note that the number of nucleons (particles in nucleus = protons + neutrons)
is conserved (conservation of nucleon number), and energy is also conserved.
The decay happens spontaneously, and there is no way to predict when it will happen.
General equation:
A
A4
Z N Z 2 N '

Beta Radiation
A beta particle/wave is a high speed electron (or positron). These are higher energy than
 but less than . There are 3 types of beta radiation:
- decay (electron emitted):
32
32
15 P16 S
 e   
parent  daughter + electron + antineutrino + energy
An electron is emitted from a neutron in the nucleus, changing the neutron into a proton.
Charge, nucleon number and energy are all conserved.
Generally
A
A

Z N  Z 1 N 'e
  
+ decay (positron emitted):
22
22

11 Na10 Ne  e
  
parent  daughter + positron + neutrino + energy
A positron is emitted from a proton in the nucleus, changing the proton into a neutron.
Again, charge, nucleon number and energy are all conserved.
Generally
A
A

Z N  Z 1 N 'e
  
Electron capture (EC) by nucleus:
7
4 Be
 e  37 Li    
parent + electron  daughter + neutrino + energy
An inner electron is captured by the nucleus, changing a proton into a neutron. The rest of
the electrons fall down to fill the space. Again, charge, nucleon number and energy are all
conserved.
Generally
A
ZN
 e  Z A1 N '  
Gamma Radiation
Very high energy (frequency) photons (no charge) are emitted by nuclei in an excited
state. These photons have a great deal of energy, and are even more powerful than X
rays. The NUCLEI are excited, not the electrons. This generally happens as a result of
previous nuclear decays, and sometimes by collisions with other particles.
12 * 12
Ex. 6 C  6 C    
Excited nucleus  ground state nucleus + gamma particle + energy
Generally
A *
A
Z X Z X
 
Type
Alpha
Power/Energy
Low
Particle (charge)
4
He nucleus (+)
Beta
Medium
- Electron (-)
+ Positron (+)
EC Orbital electron (-)
Gamma
High
Photon (none)
A
ZN
Equation(s)
 A-4Z-2N’ + 42He + 
A
A

Z N  Z 1 N 'e    
A
A

Z N  Z 1 N 'e    
A

A
Z N  e Z 1 N '  
A *
A
Z X Z X    
Decay Series
Often an unstable nucleus can decay in two or more different ways, and can produce
another unstable nucleus as its daughter. Then this new nucleus can also decay in several
ways. This creates a decay series, or chain, finally ending with a stable element. (see Blue
Book p. 933)
Recommended problems: Blue book p. 939 Q1, 2, 3, 5, 8, 11*, 12*, 13*, 18, 19
(must do 11-13!!)
Red book p. 621 #5-8, p. 624 Concept Review,
p. 636 R2, 3, 5, 10, A1, 3, 5, P 4, 5, 6, 7
Lesson #2
Energy-Mass Equivalence
**********Not doing this demo in 2003 – Sorry, No Time!!******************
Geiger Counter Demo
Explain  source,  source, ( source)
What are the particles? Write the decay equations?
1. Distance (GAMMA SOURCE)
a. Count clicks for 1 min at distance of infinity, 60 cm, 50 cm, …, 10 cm
b. Plot
2. Shielding (BETA SOURCE)
a. At fixed distance, count clicks for 1 min with shields of same thickness if
possible (foil, paper, lead, glass,…)
**************************************************************
Energy-Mass Equivalence
E = mc2 is one of the most used and least understood expressions in science. It relates
energy to mass. It applies for all processes, but is most noticeable for nuclear reactions.
Binding energy (or mass defect) of a nucleus.
Stable nuclei do not spontaneously fall apart, but they are constantly repelled from each
other due to Coulomb repulsion. If we want to blow them apart, we must add energy. The
amount of energy needed to separate the particles is called the binding energy of the
nucleus.
Ex. Determine the mass defect and binding energy of carbon 12.
Individual particles
6p + 6n + 6e
=6(1.67 × 10-27 kg) + 6(1.67 × 10-27 kg) + 6(9.11 × 10-31 kg)
=6(1.00728 u) + 6(1.008665 u) + 6(0.000549 u)
=12.098964 u
or
2.00903  10-26 kg
[see Appendix F in Blue book, or p. 721 in Red book for these values]
Group
12.0000 u × 1.6605 × 10-27 kg/u
=1.9926  10-26 kg
These have different masses, so they must have different energies. The
binding energy is
E = mdiff c2 ={(2.00903-1.9926)  10-26 kg}{2.9979  108 m/s}2
=1.47663  10-11 J or 148 MeV
Note: conversion factor between amu and MeV is 931.5 MeV/1 amu
Ex. A Uranium 236 nucleus undergoes alpha decay. Determine the amount of energy
released during this process, using the tables in the back of your text.
Equation:
236
232
192 U  90Th  

Energy before: 236.045562 u (from back of book)
Energy after: 232.038051 u + 4.002602 u + 
So =236.045562-232.038051-4.002602 u
=0.004909 u
or
0.02244754 MeV
Recommended problems
Blue book p. 940 P19, 20, 21, 22, 25, 27, 29
Red book p. 631 #13, p. 642 #1, 2, 3, 4
Fission and Fusion Assignment
1. Explain the difference between nuclear fission and nuclear fusion. Give examples.
2. Show an example of a decay equation for a fission reactor.
3. What is a chain reaction? Critical mass? Where and by whom was the first
sustained chain reaction achieved?
4. Explain how the reaction inside a fission reactor works.
5. Provide definitions for each of the following, and explain what they do in a
fission reactor.
 Control rods
 Slow neutrons
 Heavy water
 Enriched uranium
6. Explain what Canada’s contribution to fission reactor technology was (try
“CANDU reactor”) and why it is/was important.
7. What was the Manhattan Project? Describe it briefly.
8. What is your opinion about nuclear power? Outline the risks and benefits, then
make a decision about whether we (Canada, the world) should continue to
develop and use our nuclear fission reactor technology.
Nuclear Physics Problem Set / Review #1
1. Calculate
a. The approximate size of a 212Pb nucleus.
b. The atomic mass number of an atom with a nuclear radius of 2.74  10-15
m. (Remember that A must be a whole number, so round off!)
2. Determine the number of protons and neutrons in each of the following kinds of
nuclei.
a. 16O
b. 35Cl
c. 234Th
d. 1H
3. Write equations for the following nuclear decays: [the answers at the bottom of
the page give just the daughter nuclei.]
a. alpha decay of 230Th
b. beta (–) decay of 212Pb
c. beta (+) decay of 46Cr
4. Determine what type of decay causes the following transmutations:
a. 226Ra  222Rn + _____ ?
b. 214Bi  214Po + _____ ?
c. 239Np  239U + _____ ?
5. In #3 and #4 above, which reactions involved the emission of a neutrino? Which
involved the emission of an antineutrino?
6. Write the equation for the electron capture of chromium 51.
7. The mass of a Beryllium 7 nucleus is 1.1652  10-26 kg.
a. What is the difference between the mass of the nucleus and the mass of its
constituent particles, in kg?
b. What is the binding energy of this nucleus, in J?
c. What is the binding energy per nucleon of this nucleus in J?
8. If the binding energy of a lithium 6 nucleus is 4.98118  10-12 Joules, what is the
mass of the nucleus in amu?
9. **The mass spectrometer is a device used to measure the masses of different
types of particles in the same compound. The particles are separated using a
magnetic field that is perpendicular to their direction of travel. Singly charged
ions (+1e) pass through a region of magnetic field 0.250 T and electric field 7.00
 103 V/m, where the electric and magnetic forces balance each other. (The fields
are perpendicular to each other.) They then enter the region where the magnetic
field is the same, but the electric field is turned off. If the particles are deflected
by a radius of 8.12  10-3 m, what is the mass of each ion in kg? [Try to find the
speed first, then use forces to find the mass.]
Answers:
1.) a) 7.1  10-15 m, b) A = 12
2.) a) 8 p, 8 n, b) 17 p, 18 n, c) 90 p, 144 n, d) 1 p, 0
n
3.) a) 226Ra, b) 212Bi, c) 46V
4.) a) alpha, b) beta (), c) beta (+)
5.) neutrino: 3c & 4c, antineutrino: 3b & 4b
6.) 51Cr + e-  51V + e+
7.) a) 6.31  10-29 kg, b) 5.68  10-12 J, c) 8.11  10-13 J
8.) 6.01493 amu
-26
9.) 1.16  10 kg