Why are a significant number of beta particles found to have an energy smaller than the maximum?

Question

anonymous · Answer

remember that beta particles are electrons and are much smaller than an atom. So, when they travel, they pass "through" the atoms coming closer the the highly positive nucleus. This causes electrostatic interaction and slows down the beta particle. 
This is one of the many possible cases. If you elaborate the question, we can provide a more concerned reason.

anonymous · Answer

ELECTROKID,    The reason that in beta  decay  the beta particle has a distribution of energies is that the decay final state involve three particles carrying the energy and momentum.  In this situation the total energy of the final state is divided among the three particles i.e., the new nucleus, the beta particle and the neutrino.  From  classical mechanics you know that the energy can be divided among them in an infinite combination.