Belt of Stability
Nuclei above the belt of stability have too many neutrons (per proton)
They tend to decay by
β -emission, which decreases the n/p + ratio
Example
120
49
In
→
120
50
Sn
+
1
0 e
Belt of Stability
Nuclei below the belt of stability don’t have enough neutrons (per proton)
They tend to decay either by electron capture (for heavy elements) or positron emission (for light elements), both of these processes increase the n/p + ratio
118
54
Xe
+
0
1 e
→
120
53
I
Belt of Stability
Nuclei with atomic numbers greater than
83 are all unstable.
They have too many protons and neutrons.
They tend to decay by
α -emission
239
94
Pu
→
237
92
U
+
2
4 He
1

Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation.
They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).
This example shows a series of α - and β -decays that start with 238 U and end with 206 Pb
Other Considerations
Nuclei with 2, 8, 20, 28, 50, or 82 protons or 2, 8, 20, 28,
50, 82, or 126 neutrons tend to be more stable than nuclides with a different number of nucleons.
Radioactive Decay – Half Life
2

Binding Energy per Nucleon
Elements with intermediate masses have the highest nuclear binding energies
Chain Reaction
3

Nuclear Weapons
Nuclear Reactor
Nuclear Power Plant
4

Nuclear Fusion
5