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Nuclear Reactions Alpha, Beta, and Gamma Decay
Nuclear Reactions
Alpha, Beta, and Gamma Decay
State what is meant by alpha, beta and gamma decay of radionuclides.
Identify the processes occurring in nuclear reactions written in symbolic form.
The Atom
The atom consists of two parts:
1. The nucleus which contains:
2. Orbiting electrons.
protonsneutrons
All matter is made up of elements (e.g. carbon, hydrogen, etc.).
The smallest part of an element is called an atom.
Atom of different elements contain different numbers of protons.
The mass of an atom is almost entirely due to the number of protons and neutrons.
The Atom
XA
Z
Mass number
Atomic number
Element symbol
= number of protons + number of neutrons
= number of protons
XA
Z
A = number of protons + number of neutrons
Z = number of protons
A – Z = number of neutrons
Number of neutrons = Mass Number – Atomic Number
U235
92U
238
92
There are many types of uranium:
A
Z
Number of protons
Number of neutrons
A
Z
Number of protons
Number of neutrons
U235
92U
238
92
There are many types of uranium:
Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.
A 235
Z 92
Number of protons 92
Number of neutrons 143
A 238
Z 92
Number of protons 92
Number of neutrons 146
Most of the isotopes which occur naturally are stable.
A few naturally occurring isotopes and all of the man-made 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 results in the emission of either:
• an alpha particle (),
• a beta particle (),
• or a gamma ray
Radioactive Decay
An alpha particle is identical to that of a helium nucleus.
It contains two protons and two neutrons.
Alpha Decay
XA
ZY
A - 4
Z - 2+ He
4
2
Alpha Decay
unstable atom
more stable atom
alpha particle
Alpha Decay
Ra226
88
Rn222
86
He4
2
XA
Z?
A - 4
Z - 2+ He
4
2
Ra226
88Rn
222
86+ He
4
2
Alpha Decay
Rn222
86He
4
2+Po
218
84He
4
2
Rn222
86+?
A
ZHe
4
2
Alpha Decay
? A
Z+Th
230
90He
4
2
Alpha Decay
He4
2U
234
92+Th
230
90He
4
2
Th 230
90+?
A
ZHe
4
2
Alpha Decay
He4
2+Ra
226
88He
4
2Th
230
90
? A
Z+Pb
214
82He
4
2
Alpha Decay
He4
2+Pb
214
82
He4
2
Po 218
84
Beta Decay
A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.
Beta decay occurs when a neutron changes into a proton and an electron.
Beta Decay
As a result of beta decay, the nucleus has one less neutron, but one extra proton.
The atomic number, Z, increases by 1 and the mass number, A, stays the same.
Beta Decay
Po218
84
0
-1
At218
85
?A
Z?
A
Z + 1+
0
-1
Beta Decay
Po218
84Rn
218
85+
0
-1
Th234
90?
A
Z+
0
-1
Beta Decay
Th234
90Pa
234
91+
0
-1
? A
ZPb
210
82+
0
-1
Beta Decay
Tl210
81Pb
210
82+
0
-1
Bi210
83?
A
Z+
0
-1
Beta Decay
Bi210
83Po
210
84+
0
-1
? A
ZBi
214
83+
0
-1
Beta Decay
Pb214
82Bi
214
83+
0
-1
Gamma Decay
Gamma rays are not charged particles like and particles.
Gamma rays are electromagnetic radiation with high frequency.
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).
