The detection of low energy neutrons and gamma-rays by superfluid He-3, a potential dark matter detector

We have demonstrated in a pilot study using an existing experiment that superfluid He-3 at 100 mu K can be used as a nuclear recoil detector sensitive to neutron and gamma-ray interactions depositing energies down to a few hundred eV. The deposited energy is converted to He-3 quasiparticles which are detected by their effect on a vibrating wire resonator in the liquid. The system can be calibrated independently using a second vibrating wire as a heater but a convenient fixed point is provided by the exothermic reaction n + He-3(2) = p + H-3(1) + 764 keV. Given the great potential for improvement we propose that the system might make a sensitive WIMP detector.