Ranges of shielded nuclides from thermal-neutron fission

Abstract

Average ranges in Al of shielded nuclides 86Rb and 136Cs and several chain-yield species from thermal-neutron fission of 233U and 235U have been measured. The values obtained (in mg/cm2 Al) are, for 233U: 86Rb, 3.88 ± 0.04; 136CS, 2.80 ± 0.01; and for 235U: 86Rb, 3.76 ± 0.03; 136Cs, 2.81 ± 0.01. A range–energy transformation was used to determine average kinetic energies [Formula: see text] of the secondary fragments. In agreement with previous work, the shielded nuclides are found to have smaller [Formula: see text] values than neighboring chain-yield species. The deficits of [Formula: see text] are, for 233U, 4 and 8 MeV, and for 235U, 8 and 10 MeV, respectively, for 86Rb and 136Cs. Most of the range experiments were done with the thick-catcher method followed by conventional radiochemical treatment of the catcher foils. Ranges of 20 products from 233U were determined in preliminary experiments in which gross γ-ray spectra of fission products in the catcher foils were observed with a Ge(Li) detector. The kinetic-energy deficits of the shielded species are interpreted by Monte Carlo calculations of prompt-neutron emission.