Superconductive tunnel junction detectors as X-ray spectrometers

Superconductive Tunnel Junctions (STJs) are being developed as high energy resolution X-ray single photon detectors. Quasi-particle losses at the edges of such devices form a serious source of energy resolution degradation. A simple analytical relation for this source of resolution degradation has been derived from classical diffusion theory. Analyzing the X-ray spectra obtained for different series of STJs with various sizes, the edge reflectivity and the diffusion constant for our sputtered Nb films can be derived. This reflectivity can be explained by quasi-particle trapping. In addition progress is reported on the surface conditioning of single crystal, superconducting, Ta and Nb absorbers to be used for a highly efficient imaging X-ray spectrometer employing STJs as read-out.