Photofission of ¹⁹⁷Au and ²⁰⁹Bi at intermediate energies

Abstract

Recoil properties and yields of radionuclides formed in the photofission of ¹⁹⁷Au and ²⁰⁹Bi by bremsstrahlung of end-point energies (E ₀) from 300 to 1100 MeV have been investigated using the thick-target thick-catcher method. The kinetic energies T of the residual nuclei were deduced based on the two-step vector model and discussed by comparing with the reported results on protoninduced reactions as well as those on photospallation. The charge distribution was reproduced by a Gaussian function with the most probable charge Z_p expressed by a linera function of the product mass number A and with the A-independent width FWHM _CD. Based on the charge distribution parameters, the symmetric mass yield distribution with the most probable mass A _p of 92 m.u. and the width FWHM _MD of 39 m.u. was obtained for ¹⁹⁷Au at E ₀≥600 MeV. The A _p value for ²⁰⁹Bi was larger by 4 m.u. than that for ¹⁹⁷Au and the FWHM _MD was smaller by 6 m.u. A comparison with the calculations using the Photon-induced Intranuclear Cascade Analysis 3 code combined with the Generalized Evaporation Model code (PICA3/GEM) was also performed.