In alpha decay the energy and momentum are known and two particles are involved, allowing KE to be determined.
Work Step by Step
In alpha decay, assuming the parent nucleus has a known energy and zero momentum, there are just 2 pieces afterward: the daughter nucleus and the alpha particle. By applying energy and momentum conservation, E and p values of each are determined, and fall in a very narrow range. In contrast, in beta decay, there are three particles present after the decay (see section 30-5). The energy and momentum conservation equations are not enough to determine the individual energy/momentum of each particle, and a spectrum of energies is the result.