PHASE-TRANSITION TIME MEASUREMENTS OF SUPERHEATED SUPERCONDUCTING GRANULES

We investigated the phase transition time of single Sn, In and Al granules from 20 mu m up to 50 mu m in diameter. The transitions from the superconducting to the normal state were induced by ramping the external magnetic field above the superheating field or by irradiating the granules with X-ray or beta sources at a constant magnetic field. The readout electronics was optimized to allow real-time measurements with a signal resolution of 11 ns. Within the experimental errors, the irradiation measurements revealed no difference between magnetically and thermally induced phase transitions. The dependence of the transition time on the temperature, the granule size and the orientation of the sample with respect to the magnetic field is discussed. The presented results are part of an ongoing project to develop a Superheated Superconducting Granule (SSG) detector for cold dark matter search and neutrino detection.