SUPERCONDUCTING DETECTORS FOR PHOTON AND PARTICLE SPECTROSCOPY - CRITERIA FOR TRANSITIONS TO NORMAL STATE

The nonequilibrium state produced when a high energy (> 1 keV) quanta interacts with a superconducting solid is the physical basis for many new detectors. The most common approaches magnetically monitor the phase of small "grains" (SGDs) or monitor transients in the quasiparticle tunneling current in voltage-biased Josephson junctions (TJDs). While the former requires transitions to the normal state for its signal, the latter's energy resolution is degraded by excursions in the order parameter. To facilitate detector design, this article quantifies how the choices of sample material, bath temperature and field bias combine to influence the magnitude and spatial extent of the thermal excursion. Extensive tables of materials parameters are included. A wide range of inherent effects including the magnetic field dependent latent heat of the transition are discussed in the context of the limitations they produce on the operating energy range and size of proposed SGD detectors. Superheated initial conditions are not considered because the need for automatic resetting in astrophysical X-ray spectroscopy. Of the 23 elemental superconductors, we show that as SGDs only 5 have maximum grain sizes larger than 10-mu-m and only 3 are usable for photons with energies above 100 keV. Alpha particle detectors will he restricted by conceptually equivalent physics. Only by using inhomogeneous initial states or local. rather than global, transitions may these restrictions on bolometric detectors be lessened.