Low energy neutron-proton interactions

Abstract

There have been few measurements of cross sections for neutron-proton scattering and radiative capture below 1 MeV. Those measurements which do exist are at a small number of energies and are often inconsistent with theoretical models and with each other. We have conducted several experiments with the goal of obtaining improved data on these cross sections at the University of Kentucky (UKY) and the Los Alamos Neutron Science Center (LANSCE). Feasibility studies for measuring the low energy cross section for np radiative capture have been conducted at both UKY and LANSCE, culminating in a measurement of the cross section at 0.5, 0.9, 1.5, 2.0, and 2.5 MeV at UKY, using a plastic scintillator to detect recoiling deuterons and two BGO scintillators to detect the [gamma]-ray yields at 64.6° and 106.6°. We also performed measurements of the response of BC418 plastic scintillator to low energy protons during these studies, and conducted several additional measurements of the scintillator response at LANSCE and UKY, yielding very precise results from 100 keV to 3.6 MeV. The total cross section for np scattering was measured at UKY from 150 to 800 keV by neutron transmission, measuring the neutron yields in a liquid scintillator with various targets in the beam. The cross section was determined by taking ratios of neutron yields with and without the target, giving cross sections which are independent of detector efficiency and dead time. These results fill a significant gap in the available data below 500 keV.