Why alpha particles inestead of hydrogen or duetereum?

Question

I know atoms undergoing alpha decay emit alpha particles, but I was wondering why specifically helium nuclei? If these atoms wanted to emit the smallest unit of matter (I'm talking about hadrons here, not subatomic) they could just emit hydrogen nuclei, or if they wanted to emit the smallest unit of protons/neutrons attached together they could just emit deuterium. Yet for some reason, they choose to emit helium nuclei. Any thoughts?

Answer 1

This is a good question. I'm not sure that anyone really knows the answer to this for sure. However, I think that it is really an energy problem. Nuclei want to be in the lowest energy configuration. The greater the difference between the masses of the components (protons/neutrons) and the nuclear mass, the greater the binding energy of the nucleus. Greater binding energy implies higher stability.

If you do the math, I think you will find that the helium nuclei is more stable than deuterium, and emitting only a proton (hydrogen nucleus) would make the parent nucleus even more unstable. Remember, there is a "line of stability" giving the ratio of protons to neutrons for stable nuclei, a helium nucleus will keep closer to this line.