Elastic and Inelastic Scattering of Neutrons from Neon and Argon: Impact on Neutrinoless Double-Beta Decay and Dark Matter Experimental Programs

In underground physics experiments, such as neutrinoless double-beta decay and dark matter searches, fast neutrons may be the dominant and potentially irreducible source of background. Experimental data for the elastic and inelastic scattering cross sections of neutrons from argon and neon, which are target and shielding materials of interest to the dark matter and neutrinoless double-beta decay communities, were previously unavailable. Unmeasured neutron scattering cross sections are often accounted for incorrectly in Monte-Carlo simulations.;Elastic scattering cross sections were measured at the Triangle Universities Nuclear Laboratory (TUNL) using the neutron time-of-flight technique. Angular distributions for neon were measured at 5.0 and 8.0 MeV. One full angular distribution was measured for argon at 6.0 MeV. The cross-section data were compared to calculations using a global optical model. Data were also fit using the spherical optical model. These model fits were used to predict the elastic scattering cross section at unmeasured energies and also provide a benchmark where the global optical models are not well constrained.;Partial γ-ray production cross sections for (n,xnγ ) reactions in natural argon and neon were measured using the broad spectrum neutron beam at the Los Alamos Neutron Science Center (LANSCE). Neutron energies were determined using time of flight and resulting γ rays from neutron-induced reactions were detected using the GErmanium Array for Neutron Induced Excitations (GEANIE). Partial γ-ray production cross sections for six transitions in 40Ar, two transitions in 39Ar and the first excited state transitions is 20Ne and 22Ne were measured from threshold to a neutron energy where the γ-ray yield dropped below the detection sensitivity. Measured (n,xnγ) cross sections were compared with calculations using the TALYS and CoH3 nuclear reaction codes. These new measurements will help to identify potential backgrounds in neutrinoless double-beta decay and dark matter experiments that use argon or neon. The measurements will also aid in the identification of neutron interactions in these experiments through the detection of γ rays produced by ( n,xnγ) reactions.