DYNAMICS OF RADIATION-INDUCED QUASI-PARTICLES IN SUPERCONDUCTING TUNNEL JUNCTION DETECTORS

In order to achieve a high resolution in the spectroscopy of low energ y X-rays, detectors based on superconducting tunnel junctions as senso rs are presently investigated. The knowledge of the processes affectin g the signal generation in such sensors is essential for the interpret ation of the detector response. Starting from a diffusion model includ ing decay and tunneling of excess quasiparticles in the metal layers o f a superconducting tunnel junction detector, the detector response is determined as a function of absorption position and of rate constants . Model predictions agree very well with experimental data. The advant ages of a detector employing quasiparticle trapping are pointed out an d the parameters determining the signal gain are deduced. The linearit y of the detector signal is much more affected by pair recombination o f the quasiparticles during their tunneling rather than during their d iffusive propagation into the tunneling region.