Neutron-Deuteron Elastic Scattering Measurements

Abstract

Neutron-deuteron elastic scattering is important for critical systems involving heavy water, including the CANDU (Canada Deuterium Uranium) reactor. A change of the elastic scattering angular distributions included in the ENDF/B-VI.5 evaluated data file for deuterium (and retained in ENDF/B-VII) has led to significant changes in Calculation/Experiment (C/E) for LANL critical benchmark experiments containing heavy water and a small, but noticeable, change in C/E for coolant void reactivity experiments relevant for CANDU reactors. Follow-up involved first principles nuclear model calculations to obtain revised angular distributions from Faddeev 3-body theory, state of the art nucleon-nucleon forces, three-body and magnetic moment interactions. The calculated differences which are most pronounced occur in the domain just above the onset of anisotropy at 50-100 keV. Here, earlier measurements show contradictory results about the magnitude of this anisotropy. At IRMM measurements are carried out in the energy range from 100 keV to 2 MeV to test the angular distributions of neutron-deuteron elastic scattering at angles where predictions show the largest differences (backward angles). An enriched sample (99.999% purity of deuterium ), consisting of a molded polyethylene disc 70 mm in diameter and 3 mm thick, was prepared and delivered through AECL. Measurements are performed at the GELINA facility using a new setup based on detection of scattered neutrons using two HPGe detectors. In front of each detector a B4C converter is used. Meanwhile we started another project to detect the recoiling deuterium using a state of the art TPC (time projection chamber) filled with deuterated P10 gas.