What is a quasibound state and how is it different from a bound state?

I have read this term in nuclear physics in the context of compound nucleus formation. A compound nucleus $C$ is formed by the absorption of a projectile 'a' (say a nucleon) by a target nucleus which is called a quasibound state.

The current answer by @Paul defines a quasibound state as a metastable state around a local minimum. But how can the nuclear potential, which is of Woods-Saxon type, have quasibound states? It does not seem to have a local minimum like the one shown below.


1 Answer 1


A quasibound state is a state that can exist in a local minimum, which does not necessarily correspond to the global minimum. Quantum tunneling then limits the lifetime of these states. More general, it corresponds to a resonant state in a potential through which the wave function can tunnel. In the figure below, curve (a) represents a bound state, curve (c) a dissociative state and curve (b) a quasibound state. Such states are also referred to as shape resonances.

a) bound state, b) quasibound state, c) dissociative state

  • $\begingroup$ How can nuclear potentials (which are of Woods-Saxon type) have quasibound states? It does not seem to have a local and a global minimum. Thanks $\endgroup$ Jan 15, 2022 at 6:46
  • $\begingroup$ Have a look at alpha decay. $\endgroup$
    – Paul
    Jan 15, 2022 at 9:36
  • $\begingroup$ You may also wanna look at the quasibound $A$ state of the helium molecule (i.e., helium excimer) as an interesting case. For a long time it was thought that the helium molecule should be in an excited state to physically exist without dissociation. It was in the 90s that a stable helium molecule in the ground state was detected. $\endgroup$
    – Newbie
    Jan 15, 2022 at 14:12

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