Why is Helium 4 so stable?

Question

I've been looking at stuff to do with binding energies and was wondering why Helium 4 is so stable. The fact everything up to carbon is less stable seems a bit odd. Is there a reason for this or another, that's how the universe works?

Pieter · Accepted Answer

If one regards the nucleus as a potential well for nucleons, there is one lowest level. It can contain:

a spin-up proton
a spin-down proton
a spin-up neutron
a spin-down neutron

Then that lowest level is full. Any additional nucleons can only find a place in levels with higher kinetic energy.

blanci · Answer

Yes as Pieter mentions being fermions with Pauli exclusion you can get a spin up and a a spin down in the same ground state for both n and p. Like in atomic physics you can put 2 electrons in the s orbital.
In addition a geometric effect that 4 particles can be arranged in a tetrahedron shape with each ball touching the other 3 giving a very high binding energy per nucleon compared to say 3 nucleons. So that may explain why He4 is ejected in preference to He3 or He2 or H3 or dineutron or often even in preference to a single proton or neutron.

Why is Helium 4 so stable?

2 Answers

Add your own answers!

Ask a Question