# What does it mean for a nucleus to be more stable?

When we say that a nucleus is more stable than another nucleus, are we saying that the nucleus is at a lower energy level than the other nucleus? In chemistry, a more stable compound is one that is at a lower energy level, is this the same when we talk about a nucleus?

If yes, wouldn't this make all nuclei with a larger mass more unstable since they will be at a higher rest mass energy. But clearly, this is not the case as the binding energy per nucleon graph increases initially before decreasing, suggesting that a heavier nuclei can be more stable than a lighter one.

• Jul 7, 2021 at 9:51

This is not quite identical to the stability of chemical compounds. The nuclei can be often treated as isolated, so that the value of their decay rate is dominated by the strength of their coupling to the environment. Temperature and hence the excitation energy play minor role in this respect (although they certainly matter, e.g., when considering many nuclei in a nuclear reactor). On the other hand, chemical compounds are nearly always a part of a solution or a gaseous mixture, and their decay rate varies significantly with temperature according to the activation law: $$\Gamma\propto e^{-\frac{E_b}{k_BT}},$$ where $$E_b$$ is the binding energy.