Types of Nuclear Decay
Mike Jones
Pisgah High School
Canton NC
Revised 011708
Alpha () emission (NC Chem)
A type of fission that produces a stable, low energy particle, the alpha particle. Alpha decay occurs with heavier
elements; generally above Z=78. An alpha particle is equivalent to the nucleus of a helium atom and contains two
protons and two neutrons. The symbol for the alpha particle is 2He4.
A
4
A-4
ZX  2He + Z-2Y
Beta– ( -) emission (NC Chem)
A process that involves the weak force and the carrier of the weak force, the W boson. In beta decay a down-quark
in a neutron (udd) is converted into an up-quark to make a proton (uud), and the emission of the W- boson. The Wboson decays to form an electron (beta) and an anti-neutrino. The W (and Z) bosons are the particles that carry the
weak force. The weak force is one of the four fundamental forces in nature: strong, weak, electromagnetic, and
gravity. The symbol for the beta- particle is -1e0
A
0
A
ZX  -1e + Z+1Y
Bosons are “force carriers”, and are usually composite particles that are associated with the emission of energy. Some
examples of bosons are photons which carry the electromagnetic force; the W and Z bosons which mediate the weak force
(associated with the decay of neutrons); gluons which mediate the force needed to hold the nucleus together; and the Higgs
boson (which is as yet undiscovered) which is thought to be involved in the interchange between matter and energy.
Beta+ (+) emission, also known as positron emission
In positron emission everything is reversed. An up-quark in a proton changes into a down-quark and forms a
neutron, emitting a W+ boson, which decays to form a positron (an anti-electron) and a neutrino. Positron emission
can be easily detected by the annihilation gamma radiation that is produced when the positron (antimatter)
combines with an electron to completely annihilate one another. The gamma radiation that is produced has a
characteristic energy and wavelength that is easily identified. The symbol for the positron is +1e0
A
0
A
ZX  +1e + Z-1Y
Electron capture
In its simplest form, electron capture occurs when an inner electron is “captured” in the nucleus and interacts with a
proton and produces a neutron. In a bit more detail, the electron that is capture in the nucleus decays into a neutrino
and the W+ boson which in turn interacts with a proton to “flip” an up-quark into a down-quark and thereby convert
the proton into a neutron.
A
0
A
ZX + -1e  Z-1Y
Internal transition (or internal conversion)
This is a type of radiation which appears to be beta emission, when in fact, there is no transmutation. Energy is
emitted from an excited nucleus and absorbed by an electron outside the nucleus. The electron acquires enough
energy to be ejected from the atom, giving the appearance of beta radiation.
Gamma () emission (NC Chem)
During the transmutation processes accompanying various forms of nuclear decay, the nucleus may be left in an
“excited state” with an “excess” of energy. The nucleus sheds this “extra” energy and returns to a lower-energy
state by emitting energy in the form of high energy (short wavelength) photons, or gamma radiation. As in the case
of many different wavelengths of light being emitted by electrons moving from higher to lower energy levels, many
different wavelengths in the gamma ray range of the electromagnetic spectrum are emitted producing identifiable
gamma-ray spectra. Gamma rays are also emitted when matter and antimatter annihilate each other.
Chemistry Worksheet Date _______________________ Period __ Name ________________________________
Types of Nuclear Decay
Alpha () emission
A type of fission that produces a stable, low energy particle, the alpha particle. Alpha decay occurs with heavier
elements; generally above Z=78. An alpha particle is equivalent to the nucleus of a helium atom and contains two
protons and two neutrons. The symbol for the alpha particle is 2He4. Alpha emission is sometimes referred to as a
form of nuclear fission, where the atom splits into a decay product and an alpha particle.
ZX
Example of alpha decay:
Th 
232
90
228
88
A
 2He4 +
Z-2Y
A-4
Ra  24 He
Beta– ( -) emission
A process that involves the weak force and the carrier of the weak force, the W boson. In beta decay a down-quark
in a neutron (udd) is converted into an up-quark to make a proton (uud), and the emission of the W- boson. The Wboson decays to form an electron (beta) and an anti-neutrino. The W (and Z) bosons are the particles that carry the
weak force. The weak force is one of the four fundamental forces in nature: strong, weak, electromagnetic, and
gravity. The symbol for the beta- particle is -1e0.
ZX
Example of alpha decay: 146 C  147 N 
A

-1e
0
+
Z+1Y
A
0 
1
e
Gamma () emission
During the transmutation processes accompanying various forms of nuclear decay, the nucleus may be left in an
“excited state” with an “excess” of energy. The nucleus sheds this “extra” energy and returns to a lower-energy
state by emitting energy in the form of high energy (short wavelength) photons, or gamma radiation. As in the case
of many different wavelengths of light being emitted by electrons moving from higher to lower energy levels, many
different wavelengths in the gamma ray range of the electromagnetic spectrum are emitted producing identifiable
gamma-ray spectra. Gamma rays are also emitted when matter and antimatter annihilate each other.
Example of gamma decay:
137
56
Ba*  137
56 Ba  
Fission
The splitting of the nucleus of an unstable atom into two smaller atoms is “fission”. Only certain heavy elements
can undergo fission. Some atoms undergo spontaneous fission, where the unstable atom simple splits apart. Most
fission reactions occur when the nucleus absorbs a slow-moving neutron, making it unstable, and then it splits.
Example of a spontaneous fission reaction:
92
1
1
1
U  141
56 Ba  36 Kr  0 n  0 n  0 n
236
92
Fusion
The combining of two simple atoms to make a more complex atom. The process is carried out in stars as new,
heavier elements are made during the lifetime of the star.
Example of a fusion reaction:
3
1
H  12 H  24 He  01n  
Nuclear Chemistry Worksheet
1. Germanium-75 decays by beta emission. Determine the decay product.
a. As-74
b. As-75
c. Ga-75
d. Zn-71
e. Zn-75
2. An alpha particle is emitted when Th-223 decays. What is the decay product?
a. Pa-219
b. Pa-223
c. Ra-219
d. Ra-223
e. Rn-221
3. Which is a correctly written decay equation?
a. 94Po210  92U210 + 2He0
b. 53I128  4He2 + 49In126
c. 13Al28  14Si28 + -1e0
d. 35Br80  0e-1 + 35Br81
e. 94Pu245  40Zr92 + 54Xe132
4. After 6 seconds, the mass of a sample of radioactive material has decreased from 100 grams to 25 grams. Its
half-life must be
a. 1 s
b. 2 s
c. 3 s
d. 4 s
e. 6 s
5. Which best describes this reaction? 92U235 + 0n1  54Xe138 + 38Sr96 + 20n1
a. This is a fission reaction equation
b. This is a fusion reaction equation
c. This is an alpha decay equation
d. This is a beta decay equation
e. This is a gamma decay equation
6. For any radioactive material, how is its half-life described?
a. It first decreases and then increases.
b. It first increases and then decreases.
c. It increases with time.
d. It decreases with time.
e. It stays the same.
7. If the half-life of a substance is 5 seconds, when will it cease to be radioactive (i.e. it ceases emitting particles)?
a. After 5 seconds.
b. After 40 seconds.
c. After 20 days.
d. After 3 months.
e. After a very long time.
8. You detect a high number of alpha particles every second when standing a certain distance from a radioactive
material. If you triple your distance from the source, the number of alpha particles you detect will decrease. By
what factor will it decrease?
a.
3
b. 3
c. 9
d. 27
e. It will stay the same.
The following questions are NOT multiple choice. Do each part.
9. You have 5 grams of radioactive substance A and 5 grams of radioactive substance B. Both decay by emitting
alpha-radiation, and you know that the higher the number of alpha-particles emitted in a given amount of time,
the more dangerous the sample is. Substance A has a short half-life (around 4 days or so) and substance B has a
longer half-life (around 10 months or so).
a. Which substance is more dangerous right now? Explain.
b. Which substance will be more dangerous in two years? Explain.
10. Write the nuclear equations (A  B + C) for the following reactions.
a. The alpha decay of 88Ra219
b. The beta decay of 63Eu158
c. The beta decay of 22Ti53
d. The alpha decay of 83Bi211
11. A certain radioactive material has a half-life of 8 minutes. Suppose you have a large sample of this material,
containing 4.0x1025 atoms.
a. How many atoms decay in the first 8 minutes?
b. Does this strike you as a dangerous release of radiation? Explain.
c. How many atoms decay in the second 8 minutes?
d. What is the ratio of the number of atoms that decay in the first 8 minutes to the number of atoms that decay
in the second 8 minutes?
12. An evil scientist has hidden in his secret laboratory 100 grams each of two radioactive substances, which we
shall simply call A and B. Both emit alpha-radiation. Substance A has a half-life of 10 days and substance B
has a half-life of 300 days.
How many grams of substance A will there be after 30 days? How will this compare to the amount of B that
remains after 30 days? Which sample (A or B) is more dangerous after 30 days have passed? Be sure to
explain your answers.
13. What is a “nuclear chain reaction”? What is “critical mass”?
14. What is the purpose of controls rods in a nuclear reactor? What is the purpose of a moderator in a nuclear
reactor?
15. At a nuclear power station, what is found in the containment building?