DIFFERENTIAL NEUTRON THERMALIZATION. Annual Summary Report, October 1, 1960 through September 30, 1961

Activities in a program of studies on the interaction mechanisms by which neutrons exchange energy with H atoms are reported. Above about 1 ev these may be regarded as collisions of neutrons with free H atoms, but at lower energles they must be regarded in terms of excitations causing molecular thermal motions determined by binding forces. Neutron thermalization is concerned with the distribution of energy levels and the probability of excitation by neutron collision. Particular emphasis was placed on studies of scattering in very low temperature materials where binding effects are most apparent, and of low energy neutron scattering. Experiments in these areas of interest were carried out with neutrons from a pulsed linear accelerator. Energy distributions in various moderating materials at 295 to 4 deg K were studied by time-of-flight analysis. Included are discussions of experimental techniques, experimental data, and conclusions concerning the dynamic behavior of various hydrogenous substances. (J.R.D.