High-precision Measurement of the 16O(n,n′γ) Cross Section using γ-ray Detection in Liquid Scintillators with H2O and BeO Targets

Abstract

The ¹⁶O($n,n^{\prime }\gamma$) reaction was measured at the Los Alamos Neutron Science Center white neutron source using γ-ray detection in liquid scintillators present in the upper hemisphere of the Correlated Gamma-Neutron Array for sCattering (CoGNAC). Separate measurements of this reaction were performed using H₂O and BeO targets in successive years. The unique high energies of γ rays emitted from the ¹⁶O($n,n^{\prime }\gamma$) reaction facilitated a clean selection of this reaction from threshold to 9.8 MeV incident neutron energy without the need for precise measurements of the γ-ray energy or the scattered neutrons. The precise time resolution of the liquid scintillator detectors was then exploited to obtain high-resolution incident neutron energy measurements, and good agreement was obtained between the H₂O and BeO results reported here. The dominant literature data sets for this reaction have systematic differences between them, but the present results improve upon the neutron energy resolution of earlier measurements and show important discrepancies in recent data. Tentative data are also shown up to 20 MeV incident neutron energy but are potentially subject to improved understanding of the relative γ-ray and α decay branches from ¹⁶O excited states.