ENERGY AND ANGULAR DISTRIBUTIONS OF PHOTONEUTRONS PRODUCED BY 70-MEV. X-RAYS

The angular distributions of the photoneutrons produced by 70-Mev. X-rays in seven elements have been measured with a zinc sulphide – lucite scintillation detector. For the heavy elements the distributions are essentially isotropic, indicating the predominance of the evaporation process, while for the light elements there is also an anisotropic component peaked at 90°. The energy distributions of the photoneutrons produced in copper and lead targets have been determined with nuclear emulsions. It is shown that most of the neutrons can be attributed to an evaporation process which is governed by a constant nuclear temperature, the temperature found for copper being 1.2 Mev., and for lead being 1.0 Mev. A high-energy tail on the energy distributions is attributed to direct interactions.