Why are alpha particles invariably emitted rather than. say. individual protons or 2H93 nuclei? The answer follows from the high binding energy of the o-particle. To escape from a nucleus, a particle must have kinetic energy, and the o-particle mass is sufficiently smaller that of its constituent nucleons for such energy to be available. The kinetic energy T released when various particles are emitted by a heavy nucleus is given by. T={mi mf m}c2 where mi is the mass of the initial nucleus, m is the mass of the nal nucleus, and m is the particle mass. The result is that only the emission of o-particle is energetically possible, other decay modes would require energy to be supplied from outside the nucleus. The alpha decayin Q2U232 is accompanied by the release of 5.4 MeV, while 6.1 MeV would require for proton and 9.6 MBV for zHe3 nucleus. The observed disintegration energies in cc-decay agree with the corresponding predicted values based upon the nuclear masses involved