Investigation of superconducting grains for low energy neutrino or dark matter detection

The feasibility of constructing a detector for low energy neutrinos or dark matter candidates from superheated superconducting grains was studied by investigating the supercooling (SC) and superheating (SH) properties of single Sn and Sn(99%)/Sb(1%) grains. When the grains were rotated around an axis perpendicular to an applied magnetic field and the SC and SH fields were measured, each grain was found to have a characteristic SC and SH field that depended on the rotation angle. A model is presented in which the dependence of the SH field of the grain as it is rotated in the applied field is related to the position on or near the surface of a nucleation center. The addition of 1 % Sb to Sn grains showed the expected shift in the effective SC and SH fields due to the increase in the ratio of penetration depth to coherence length, but the smaller grains (<40μm diameter) showed no improvement in the (undesirable) dependence of the SC and SH fields on rotation angle. However, larger (∼ 250 μm diameter) grains, because of the increased number of nucleation centers showed a reduced dependence of the characteristic SC and SH field on rotation angle