Measurements of the diffusion parameters in diphenyl at temperatures from 20 °C to 170 °C

Diffusion coefficient, mean life time of thermal neutrons, coefficient of diffusion cooling and diffusion length in diphenyl at temperatures 20°, 40°, 60°, 80°, 110°, 140° and 170° C were measured by the pulse method. Their dependence on the temperature of diphenyl was deduced in an analytic form and the change of the neutron transport length was determined experimentally. No discontinuity of the diffusion coefficient at the melting point of diphenyl apart from that caused by density change was observed. The energy exchange cross sectionM ₂ is practically independent of temperature in the range from 20 °C to 170 °C and the deduced microscopic absorption cross section for hydrogen equals 337±2 millibarns. The thermalization of neutrons in diphenyl proceeds more slowly than in water and neutrons loose their energy predominantly by interaction with the C—H group of the diphenyl molecule.We are indebted to Mr. J.Jadavan and Mr. J.Jirou for their technical assistance during the measurements and setting up the measuring apparatus.