The scattering of He 3 by He 4

Abstract

Cross sections for the elastic scattering of He 3 by He 4 have been measured for incident He 3 energies in the range 2.5 ≦ E He 3 ≦ 5.7 MeV (lab system) using a Van de Graaff accelerator and a differentially pumped gas scattering chamber. Excitation functions were measured at centre-of-mass angles 54°44′, 63°27′, 73°57′, 90°2′, 104°38′, 106°36′, 116°37′, 125°19′ and 140°50′. Angular distributions were measured at E He 3 = 2.467, 3.600, 4.761 and 5.703 MeV. The scattering phase shifts were obtained from these data. The general trend of the S-wave phase shift with energy is similar to that for hard-sphere scattering with a radius R = 2.8 fm, although there is some indication of a systematic departure from this. The variation of the δ 1 + phase shift with energy is consistent with the effect of the Be 7 ground state, calculated using single-level dispersion theory. However, the behaviour of the δ 1 − phase shift cannot be explained by the effect of only the Be 7 first excited state. The presence of the second excited state in Be 7 explains the behaviour of the δ 3 + phase shift fairly well. The parameters used for this state were J π = 7 2 −, R = 4.4 fm, characteristic energy = 3.56 MeV, reduced width = 0.7 MeV .