ALTERNATIVE NONEQUILIBRIUM SUPERCONDUCTING X-RAY-DETECTORS

Non-equilibrium X-ray detectors based on isotropic superconductor abso rbers offer the hope of energy resolution limited by the statistics of excitation production, i.e., delta E/E similar to(Delta/E)(1/2), wher e Delta is the superconducting gap energy. This can be numerically equ al to that of the best bolometers at significantly higher operating te mperatures. Superconducting Tunnel Junction Detectors (STJDs) count th e X-ray event induced excitations (quasiparticles (QP)) as an excursio n of the subgap tunnel current. While STJDs are presently the best stu died QP readout scheme, they have made slow progress toward the limiti ng energy resolution. Some of the difficulties are enumerated herein a nd are inherent in tunnel junctions. One alternative is to measure the conductivity excursion of a superconducting film that follows photon absorption. This excursion obeys exactly the same equation as the effe ctive quasiparticle tunneling conductivity in a Josephson junction. He nce the two schemes should produce the same readout waveforms when the same superconducting absorbers are used. Seven specific approaches to realizing the measurement are presented. All versions of the conducti vity readout offer simpler sample fabrication than STJD. Any supercond ucting material may be used. In commercial applications, the obvious b enefit in operating temperature of using the HTSC materials may more t han compensate for the penalty in energy resolution.