Nuclear Structure and Stability. Why do some isotopes decay and others don’t? Generally, the less energy a nucleus has, the less likely it is to decay Nuclei move in the direction of lower energy. What is holding the nucleus together in the first place?
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Nuclear Structure and Stability
The Strong Force
n0
n0
n0
p+
p+
p+
1.5 fm
p+
p+
8 fm
Nuclear Levels and Pauli Exclusion
1g9/2
2p1/2
1f5/2
2p3/2
1f7/2
1d3/2
2s1/2
1d5/2
1p1/2
1p3/2
1s1/2
16N 16O + e +
Carlson’s rules for stability:
1g9/2
2p1/2
1f5/2
2p3/2
1f7/2
1d3/2
2s1/2
1d5/2
1p1/2
1p3/2
1s1/2
Rule 1: Nuclei prefer to have approximately equal numbers of protons and neutrons, Z ½A *
*  This rule will later require modification
Rule 2: Isotopes with even numbers of protons and/or neutrons are more stable
Rule 3: Isotopes with N or Z = 2, 8, 20, 28, 50, 82, 126 are especially stable
Rule 1: Nuclei prefer to have approximately equal numbers of protons and neutrons, Z ½A *
Rule 1: Nuclei prefer to have approximately 50% (A < 50) to 40% (A > 150) protons
Rule 1: Nuclei prefer to have approximately 50% (A < 50) to 40% (A > 150) protons
Rule 4: Small A is more stable (A 200)
Rule 2: Isotopes with even numbers of protons and/or neutrons are more stable
Rule 3: Isotopes with N or Z = 2, 8, 20, 28, 50, 82, 126 are especially stable
http://www.nndc.bnl.gov/chart/
p+
p+ p+ +
p++ p+
p+
0
p+ p+ + 0
p+
p++ 0 p+
p+
p+

n0 p+ + 
n0
p+ +  n0
p+
n0