Reactions of 51V and 27Al with 7–120 MeV α-particles (equilibrium and non-equilibrium statistical analyses)

Abstract

Excitation functions for formation of 54Mn, 52Mn, 51Cr, 48V, 47Sc, 46Sc and 44mSc from 4He ion bombardment of 51V and of 22Na and 24Na from 4He ion bombardment of 27Al are reported. Incident 4He ion energies varied between 7 and 120 MeV. Mean recoil ranges are reported for all products except 48Sc. The experimental excitation functions are compared with standard statistical-model calculations, calculations using shell-dependent level densities due to Newton and to Rosenweig, calculations in which compound nucleus and particle angular momenta are coupled using a spin-dependent level density, calculations in which the s-wave approximation is performed and with Griffin's new non-equilibrium statistical model which includes intermediate resonances. No strong evidence is found for shell-structure effects on level densities in the 51V region. The calculations with spin-dependent level density give satisfactory predictions of the positions and shapes of excitation functions over the energy span for which ranges indicate a compound nucleus mechanism, using a level density parameter of a = 1 8 A. The s-wave approximation is shown to get progressively worse with increasing excitation relative to the experimental results. The extreme high-energy tails shown by many of the excitation functions are reproduced reasonably well with varying admixtures of Griffin's pre-compound particle energy distribution.