Angular Correlation of Alpha Particles from Decay of Li8

The determination of the electron-antineutrino correlation in an allowed transition has for many years constitutes a basic experimental approach to the solution of the problem of the nature of the beta-decay interaction. In the case where only the directions of the electron and antineutrino are observed, the correlation is given by [formula], where alpha has the values 1, 1/3, -1/3, -1 for vector, tensor, axial vector, and scalar interactions, respectively. As a practical matter, the direction of the antineutrino emission is deduced from coincident measurements of the vector momenta of the electron and the recoil nucleus. Even so, the experiment involves great difficulties because of the extremely low energy of the heavy recoil particle. Some years ago [1] it was pointed out that the decay of Li8 provides a particularly attractive object of study in this regard, both because the decay energy is relatively high and because the kinematics of the alpha-particle decay of the daughter nucleus, Be8*, permits extraction of the necessary information from observations on the relatively high-energy, easily detectable alpha particles.