Key Concepts
- alpha particles:
identity: helium nucleus, 42He
charge: 2+
- beta particles:
identity: high energy electrons, 0-1e
(emitted when a neutron decays to form a proton and an electron)
charge: -1
- gamma rays:
identity: high energy electromagnetic radiation (accompany alpha or beta decay)
charge: none
- Mass Numbers (A) on the left hand side of the nuclear decay equation must
equal the sum of the mass numbers on the right hand side of the equation
- Atomic Numbers (Z) on the left hand side of the nuclear decay equation must
equal the sum of the atomic numbers on the right hand side of the equation
Animated Tutorial
Examples
alpha decay
| 238 |
|
|
234 |
|
|
4 |
|
| |
U |
decays to produce |
|
Th |
and |
|
He |
| 92 |
90 |
2 |
| Mass Number (A) |
238 |
|
|
234 |
|
|
4 |
|
238 = 234 + 4 |
|---|
| |
|
U |
→ |
|
Th |
+ |
|
He |
|
| Atomic Number (Z) |
92 |
90 |
2 |
92 = 90 + 2 |
|---|
When uranium-238 decays it releases 2 protons and 2 neutrons as an alpha particle.
The daughter nucleus therefore has an atomic number (Z) = uranium's atomic number - 2
Daughter's atomic number (Z) = 92 - 2 = 90
From the periodic table we see that the element with atomic number 90 is thorium, Th.
The mass number (A) of this thorium atom = uranium's mass number - 4 = 238 - 4 = 234
The daughter nucleus (thorium-234) has 2 less protons and 2 less neutrons than the parent nucleus (uranium-238).
beta decay
| 14 |
|
|
14 |
|
|
0 |
|
| |
C |
decays to produce |
|
N |
and |
|
e |
| 6 |
7 |
-1 |
| Mass Number (A) |
14 |
|
|
14 |
|
|
0 |
|
14 = 14 + 0 |
|---|
| |
|
C |
→ |
|
N |
+ |
|
e |
|
| Atomic Number (Z) |
6 |
7 |
-1 |
6 = 7 + -1 |
|---|
When carbon-14 decays, a beta particle is released from the nucleus.
A beta particle has a mass number of 0 and an atomic number of -1.
The daughter nucleus therefore has an atomic number = carbon's atomic number - -1
Daughter's atomic number = 6 - -1 = 6 + 1 = 7
From the periodic table we see that the element with atomic number 7 is nitrogen, N.
The mass number of this nitrogen atom = carbon's mass number - 0 = 14 - 0 = 14
The daughter nucleus (nitrogen-14) has 1 more proton and 1 less neutron than the parent nucleus (carbon-14)
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