The Energy Distribution of Photoneutrons Produced by 150-MeV Electrons in Thick Beryllium and Tantalum Targets

Electron-photon cascade calculations and photoneutron-production calculations have been carried out for 150-MeV electrons on thick targets of Be and Ta. In the energy region of the giant resonance an evaporation model was used to calculate the production spectrum, and at higher energies (25 MeV) an intranuclear-cascade model was used. The calculated photoneutron-production spectra cover the energy range 0.01 to ∼100 MeV and are given for target thicknesses of 1 and 20 radiation lengths in both Ta and Be. A method is described and sufficient information is given so that estimates of the photoneutron-production spectra in targets of intermediate thicknesses may be obtained. Results on the photoproton-production spectra are also given. The spectra from the Ta and Be targets are compared and are found to have very different characteristics in that the number of low-energy (< 1 MeV) neutrons produced in the Ta target is much greater than that produced in the Be target and the number of high-energy ( a few MeV) neutrons produced in the Be target is larger than that produced in the Ta target.