The effect of angular momentum on charged particle-induced fission at moderate excitation energies

Abstract

A study has been made of the effect of varying the amount of angular momentum possessed by the projectile particle on the fission probability of some elements lighter than polonium. The same compound nucleus with approximately the same excitation energy (±0·5 MeV) was produced by nuclear reactions using different charged particles, thus depositing varying amounts of angular momentum in the compound nucleus. All analyses were done using standard radiochemical techniques. The helium ion-induced fission of 195Pt at an excitation energy of 32·7 MeV resulted in a total fission cross-section of 2·2 μbarn, while the deuterium ion-induced fission of 197Au at the same excitation energy had a total fission cross-section of 4·6 μbarn for the same compound nucleus, 199Hg ∗. The helium ion-induced fission of 207Pb at excitation energies of 33·5 and 25·6 MeV occurred with total fission cross-sections of 3080 μbarns and 27·2 μbarns respectively. The deuterium ion-induced fission of 209Bi giving the same 211Po ∗ compound nucleus at approximately the same average excitation energies had total fission cross-sections of 330 and 4·0 μbarn respectively. In the first case, the fission reaction induced by the lighter projectile nucleus occurred with a larger total fission cross-section, while in the second case, the fission reaction induced by the heavier projectile nucleus possessed the larger total fission cross-section. These results indicate that the angular momentum of the impinging nucleus contributes to but is not the only factor which influences the total fission cross-section at moderate excitation energies.