Experiments on the Direct Photonuclear Effect

Abstract

An investigation has been made of the high-energy protons and neutrons emitted in irradiation with bremsstrahlung of 65-Mev maximum energy. Protons above 14 Mev were measured. The energy limit for the neutrons varied. The angular distributions of protons from carbon, aluminum, nickel, and molybdenum could be fitted with curves of the form $a+{(sin\theta +bsin\theta cos\theta )}^2$ with the maximum around 60°. The angular distributions of neutrons above 5 and 10 Mev could be fitted with curves of the form $a+b{sin}^2\theta$. The yield of protons for eight elements from carbon to molybdenum was approximately proportional to $Z$. The yield of neutrons above 7.5 Mev for 19 elements from carbon to lead was approximately proportional to $N$. Excitation curves were measured for the high-energy protons from aluminum and phosphorus. They have a threshold at about 25 Mev and rise to about 45 Mev. From there on they are nearly constant. An attempt was made to detect proton-neutron coincidences from a carbon target. No true coincidences were found. It is concluded that the measurements are in good agreement with an independent particle model but that they agree only partly with a deuteron model.