A small-sample method for studying γ-ray angular distributions from the (n, n′ γ) reaction

Abstract

Because of the technical difficulties involved in obtaining high-flux monoenergetic neutron beams of energy E n 1MeV, the use of γ-ray angular distributions from the (n, n′γ) reaction as a tool in nuclear spectroscopy has historically been restricted to the study of nuclei available in quantities of 100 g or more. A method is presented in the present work which makes it possible to study γ-ray angular distributions from the (n, n′γ) reaction, using samples containing only a few grams of the neutron scatterer material. The central features of this method are: (1) the use of a close(<1 cm) source-scatterer separation to maximize the neutron flux in the scatterer, (2) the use of a pulsed accelerator beam and time-of-flight gating to reduce background in the γ-ray detector, and (3) the use of a new approach for correcting for the distorting effect of the close source-scatterer geometry on the γ-ray angular distribution, an approach in which the corrections are applied to the theoretical angular distributions instead of to the experimental data. This method is tested using γ-ray angular distributions from the 56Fe(n, n′ γ) 56Fe and 203Tl(n, n′ γ) 203 56Fe and 203Tl(n, n′ γ) 203Tl reactions.