A HIGHLY SENSITIVE NUCLEAR RECOIL DETECTOR BASED ON SUPERFLUID HE-3-B

The excitations in superfluid(3) He have a dispersion curve in which t he energy minimum does not coincide with the momentum minimum. As a re sult, when a mechanical resonator moves through a gas of such excitati ons, normal and Andreev scattering processes introduce a large asymmet ry into the momentum exchange and the mechanical resonator experiences a very large drag force. A gas of such excitations is thus very easy to detect even at very low densities. We have exploited this effect to monitor the increase in excitation density in a small volume caused b y a particle interaction. The working volume is filled with superfluid (3) He-B at around 100 mu K. A particle undergoing an interaction in t he volume releases a shower of quasiparticle excitations which can be detected by the increase in damping on a vibrating wire resonator. A s mall hole in the container allows the excitations to leak out into the outside colder liquid to reset the working liquid to the resting stat e. Using an existing experiment we can detect nuclear recoil interacti ons depositing energies as low as 500 eV. Two simple modifications sho uld allow us to detect interactions in the 10 eV range.