A Facility for the Study of Neutron Moderation at Cryogenic Temperatures in a Light Water Pool Nuclear Reactor

Abstract

One function of a nuclear reactor employed as a research tool is the production of collimated beams of neutrons which may be used to study the atomic lattice structure of solid and liquid materials. A light water-moderated pool-type reactor is often employed in these research activities because of its relatively low cost and because its core and moderator are maintained at temperatures not far above room temperature during operation. With the reactor core assembly operating at a temperature of 283° to 310°K, the spectrum of neutrons in the beams produced is peaked in the vicinity of 1 to 2 Å, a most convenient wavelength for atomic structure studies by neutron diffraction. Studies concerned with the vibrational structure of solids and liquids and those concerned with the identification and distribution of defects in solids often require neutrons of much longer wavelengths, The intensity of neutrons from the spectrum of a nuclear reactor normally falls off by a factor of ten at the longer wavelengths of interest, This is shown in Fig. 1 for a reactor operating at 311°K.