Angular and energy distributions of α-particles in LRA fission

Abstract

Detailed experimental studies have been made on the angular and energy distributions of the long-range α-particles (LRA) emitted from 252Cf during spontaneous fission. They show that the α-particle angular distribution is peaked at an angle (made by the trajectory of the α-particle with that of either of the main fragments) of about 90° and has a FWHM of 20–30. The α-particle energy spectrum is peaked at about 15 MeV and has a FWHM of 13 MeV. We have carried out computer calculations of the trajectories of the three particles produced in LRA fission. Such calculations lead to predictions of angular and energy distributions which may be compared with the experimental ones. The calculations were carried out using a set of initial conditions determined by the statistical theory of nuclear fission. The comparison with experimental results therefore provides a test of the statistical theory. The calculated results show that the statistical theory leads to an energy spectrum which is in good agreement with the experimental one, and that reasonable agreement between the calculated and the experimental angular distribution may be obtained if it is assumed that the α-particle is emitted within a short period of time, of the order of 3 × 10 −22 s after the instant of scission.