The \(^3\) He(n, p) process is excellent for neutron detection between thermal and \(\sim\) 4 MeV because of the high cross section and near-complete energy transfer from the neutron to the proton. Traditional gaseous \(^3\) He detectors using this process typically have high levels of radiogenic backgrounds so that they cannot measure the small neutron fluxes present in underground laboratories for dark matter experiments. I propose a cryogenic liquid \(^3\) He detector that can be designed with tiny radiogenic backgrounds and efficiently measure neutron fluxes in low-flux environments.
