Question

Explain with the help of a diagram how binding energy per nucleon affects nuclear stability?

Answer 1

Mean binding energy per nucleon `(bar "B")` for the most stable isotopes as a function of mass number is shown above. This plot leads to the following inferences:

1. Light nuclides: (A < 30):
   The peaks with A values in multiples of 4. For example, \[\ce{^4_2He, ^12_6C, ^16_8O}\] are more stable.
2. Medium mass nuclides: (30 < A < 90):
   `(bar "B")` increases typically from 8 MeV for A = 16 to nearly 8.3 MeV for A between 28 and 32 and it remains nearly constant 8.5 MeV beyond this and shows a broad maximum. The nuclides falling on the maximum are most stable which turns possess high `(bar "B")` values. ⁵⁶Fe with `(bar "B")` value of 8.79 MeV is the most stable.
3. Heavy nuclides (A > 90):
   `(bar "B")` decreases from maximum 8.79 MeV to 7.7 MeV for A ≅ 210, ²⁰⁹Bi is the stable nuclide. Beyond this, all nuclides are radioactive (α - emitters).