POTENTIAL DARK-MATTER DETECTOR - THE DETECTION OF LOW-ENERGY NEUTRONS BY SUPERFLUID HE-3

Using an existing experiment we have demonstrated in a pilot study that superfluid He-3 at 100 mu K 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 He-3 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 + He-3(2) = p + H-3(1) + 764 keV. Given the great potential for improvement we propose that the system might make a sensitive weakly interacting massive particle detector.