I understand that when beta decay occurs in the nucleus, the reason that the emergent electrons possess a distribution of energies is that varying amounts of the total energy release in the reaction get shared with the neutrinos, which carry it off stealthily. Hence the distribution, which represents the energy theft by the neutrinos.
What is the physical mechanism behind the "sharing process" that furnishes the distribution? In other words, what physical process is at work in the reaction which kicks out the neutrino with a nonunique amount of energy (hence leaving both the recoiling nucleus and the electron with nonunique energies)- as opposed to other nuclear reactions where, for example, a gamma ray gets emitted, always with a certain very well-defined characteristic energy?
