Anomalous Scattering of Neutrons by Helium and thed−dNeutron Spectrum

Abstract

An investigation of the variation of the ratio of the scattering cross section of neutrons by helium and hydrogen has been made. Neutrons were obtained from a $d-d$ source partly surrounded by 3 cm of paraffin. The anomalously high cross section in helium at 1.0 Mev was found, and the helium-hydrogen cross-section ratio diminishes to about half this maximum value at 1.4 Mev. No other maxima were observed. The $d-d$ neutron spectrum was also investigated by helium recoils. The spectrum appears to be homogeneous; no evidence was found for a low energy group of neutrons with an intensity as great as 1 percent of the main group. This indicates that ${\mathrm{He}}^3$ is not formed in an excited state.