Isomer ratios of 90Y and 91Y in the fission of 235U and 238U by protons of energies 20–85 MeV

Abstract

Isomer ratios of 90Y and 91Y formed in the fission of 235U and 238U induced by protons of energies 20–85 MeV have been determined. For both 90Y and 91Y the isomer ratios are always higher in 235U fission than in 238U fission. Isomer ratios of 90Y in 238U fission and those of 91Y in 235U and 238U fission remain almost constant in the energy range of 20–85 MeV, whereas those of 90Y in 235U fission increase with increasing bombarding energy. A theoretical calculation of these ratios indicates that the primary fragments leading to the formation of these isomers possess [Formula: see text] units of angular momentum.