Measuring (n,f) cross-sections of short-lived states

Abstract

In order to test theories of fission cross-sections, it is desirable to measure the (n,f) cross-sections of both an isomeric state and the ground state of the same isotope of the same element. This would test the ability to calculate effects that depend only on spin and parity without the confusion of effects that depend on (Z,A). At present there is no isotope for which the (n,f) cross-section has been measured successfully at MeV energies, where theoretical predictions can be made. There have been a few measurements of the cross-section U235m at thermal and cold energies. At these energies the cross-section is expected to be dominated by incalculable resonances, so that it may not be a useful test of theoretical predictions. I suggest methods for measuring the (n,f) cross-sections to neutrons with a fission spectrum of 1/2+ (26 m) isomeric U235m and of 1- (16 h) (shorter lived than the isomer) Am242gs.