LANL II Neutron Dark Scattering Analysis

The MoNA Collaboration studies the properties of unstable neutron rich isotopes at the drip line. Using an array of highly efficient MoNA neutron detectors, we measure the energy and momentum of decay neutrons to determine the properties of the parent nucleus. Neutron scattering in our detectors is complex as it involves both H and C scattering. To interpret our results, we rely on Monte Carlo simulation. Our first neutron scattering experiment at the LANSCE facility revealed significant disagreements between data and simulation, especially at higher neutron energies. Our second LANSCE experiment was designed to focus on neutron "dark" scattering arising from elastic n-C scattering (which produces light below detector threshold). The three main sources of background for our dark scattering measurements are cosmic muons, "wrap around" neutrons, and scattered beam neutrons. The scattered beam neutrons are present whenever the neutron beam is on and unable to be isolated, causing them to be the major source of background and most challenging to remove. We used data from target-out runs to develop a method to subtract scattered beam contributions. Resulting angular distributions for dark scattered neutrons, and methods used to remove background contributions, will be presented.