Mitigation of backgrounds from cosmogenic ¹³⁷Xe in xenon gas experiments using ³He neutron capture

¹³⁶Xe is used as the target medium for many experiments searching for 0νββ. Despite underground operation, cosmic muons that reach the laboratory can produce spallation neutrons causing activation of detector materials. A potential background that is difficult to veto using muon tagging comes in the form of ¹³⁷Xe created by the capture of neutrons on ¹³⁶Xe. This isotope decays via beta decay with a half-life of 3.8 min and a Q _β of ∼4.16 MeV. This work proposes and explores the concept of adding a small percentage of ³He to xenon as a means to capture thermal neutrons and reduce the number of activations in the detector volume. When using this technique we find the contamination from ¹³⁷Xe activation can be reduced to negligible levels in tonne and multi-tonne scale high pressure gas xenon neutrinoless double beta decay experiments running at any depth in an underground laboratory.