Potential Dark Matter Detector? The Detection of Low Energy Neutrons by Superfluid3He

Using an existing experiment we have demonstrated in a pilot study that superfluid ${}^3$He at 100 μK can be used as a nuclear recoil detector sensitive to neutron and $\gamma$ interactions depositing energies down to a few hundred eV. The deposited energy is converted to ${}^3$He quasiparticles which are detected by their damping effect on a vibrating wire resonator in the liquid. The system can be calibrated independently but a convenient fixed point is provided by the exothermic reaction $n+{}_2{}^3{}_{}{}^{}H\mathrm{e}=p+{}_1{}^3{}_{}{}^{}H+764\mathrm{}$ keV. Given the great potential for improvement we propose that the system might make a sensitive weakly interacting massive particle detector.