Photonuclear reactions near threshold

Abstract

A number of photonuclear reactions have been studied using the University of Saskatchewan betatron as a source of high energy x-rays. The gamma neutron threholds and reaction cross sections have 100% abundance in one stable isotope. These reactions have been studied by observing the emitted neutrons with a boron trifluoride counter in a tank of paraffin. From considerations regarding the shapes of the cross sections curves near threshold, evidence has been obtained which indicates that electric quadupole and magnetic dipole absorption of photons account for a large part of the reation yield, although electric dipole absorption may account for most of the reaction at higher energies.