SUPERCONDUCTING TUNNEL-JUNCTIONS AND QUASI-PARTICLE TRAPPING

The interaction of a nuclear particle or X-ray with a superconductor leads to the breaking of Cooper pairs and the creation of excess phonons and quasiparticles. The basic physics and the use of superconducting tunnel junctions as detectors of excess quasiparticles are reviewed. For superconducting absorbers of appreciable mass intrinsic limitations require the use of the phenomenon of quasiparticle trapping. The relaxation phonons released in the trapping process can also be detected and they can lead to amplification via further pair breaking. Superconducting tunnel junctions can also detect phonons produced by particle interactions in a substrate absorber. The use of series-connected arrays of junctions to achieve high sensitivity and good energy resolution is discussed.