Experimental Photo-Fission Thresholds inU23592,U23892,U23392,Pu23994, andTh23290

Abstract

An investigation of the photo-fission thresholds in $_{92}\mathrm{U}^{235}$, $_{92}\mathrm{U}^{238}$, $_{92}\mathrm{U}^{233}$, $_{94}\mathrm{Pu}^{239}$, and $_{90}\mathrm{Th}^{232}$ with a 20-Mev betatron is reported. A method of alpha-self-cancellation is described which permits the detection of fissions and the determination of threshold energies in the two highly alpha-active samples of $_{92}\mathrm{U}^{233}$ and $_{94}\mathrm{Pu}^{239}$. An investigation of the photo-neutron threshold in nitrogen and the energy calculation from mass data provided a check of the absolute energy scale obtained from voltage measurements on the betatron.