Highly Asymmetric Mass Division in Low-Energy Proton-Induced Fission of ²³²Th and ²⁴⁴Pu

Abstract

Mass yield distribution / Excitation function / Low-energy fission / 232 Th and 244 Pu / Rare earth fragments / Rapid chemical separation SummaryExcitation functions and mass yield distributions of rare earth products in the proton-induced fission of 232 Th and 244 Pu have been measured by means of an automatic rapid ion-exchange separation system for incident energies from 9 to 16 MeV. Excitation functions of highly asymmetric products with mass numbers A > 150 showed different energy dependence compared with those for typical asymmetric mass division products with mass number around A = 140 in the 232 Th(p,f) reaction while no clear different energy dependence between the products with A > 150 and A ~140 was observed in the 244 PU(/J,/) reaction. The gross feature of the highly asymmetric mass division would phenomenologically be explained by statistical considerations when they are compared in terms of the asymmetry parameters. However, the different energy dependence of highly asymmetric products between the two fission reactions might be caused by an additional fission mode or a slight shell effect of Ν = 50 in the light complementary fragments.

Bimodal Nature of Low Energy Fission of Light Actinides

“…Each target was wrapped with an aluminum sheet thick enough for stopping all fission products that would recoil out from the targets. After bombardments, radioactivities produced in each target-catcher assembly were determined by y-ray spectrometry [6,9], Angular distributions of products were measured by the recoil-catcher technique in the 15 MeV protoninduced fission of 232 Th and 244 Pu [7,17,18]. An aluminum catcher foil was mounted in a cylindrical irradiation chamber.…”

“…Two kinds of angular anisotropics for symmetric and asymmetric mass division products have been interpreted by the existence of two kinds of saddle point configurations with different nuclear temperature [7,18]. The analysis includes the contributions of the multiple chance fission in the asymmetric and symmetric mass division modes but it assumes nearly the same saddle shape § eff for the two saddle configurations.…”