[SOLVED] Why emit alphas, not other nucleon groups? 1. The problem statement, all variables and given/known data (Advanced Physics; Adams and Allday; Spread 8.18, Question Section 8.18, question 3) Why do you think helium-4 nuclei (alpha particles) are often emitted from unstable heavy nuclei whereas bundles of neutrons or protons alone are not? 2. Relevant equations ? 3. The attempt at a solution I have absolutely no idea but would love to know. I've often wondered and have been looking out for an answer with no success. The ejection of an alpha particle creates a different nucleus that sits approximately in the same place on the #neutrons vs. #protons "stability" graph. Not quite -- because the stability line curves, hence the ocassional beta emission to re-align. That explanation says it's energetically attractive to emit equal numbers of protons and neutrons but not why they come out in fours -- twos would do equally well or perhaps singly followed very soon afterwards by the "balancing" nucelon of the pair (because of leaving the nucleus in an excited, unstable state).