SUPERCONDUCTING TUNNEL-JUNCTIONS AND QUASI-PARTICLE TRAPPING

The interaction of a nuclear particle or X-ray with a superconductor l eads to the breaking of Cooper pairs and the creation of excess phonon s 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 limitation s require the use of the phenomenon of quasiparticle trapping. The rel axation phonons released in the trapping process can also be detected and they can lead to amplification via further pair breaking. Supercon ducting tunnel junctions can also detect phonons produced by particle interactions in a substrate absorber. The use of series-connected arra ys of junctions to achieve high sensitivity and good energy resolution is discussed.