X-ray and particle detection with superconducting tunnel junctions

Superconducting tunnel junctions may be used in detector applications in which an energy resolution comparable to that of crystal spectrometers is desired, but combined with the counting capability of semiconductor detectors. We have developed a detector consisting of superconducting aluminium tunnel junctions and tin absorbers. Using these superconductors with different energy gaps, potential wells for quasiparticles are established. Quasiparticles created after energy deposition in the absorber are thus concentrated in the attached superconducting tunnel junctions. A model for the propagation of quasiparticles is developed and the influence of the electrical parameters of tunnel junctions on the read-out electronics is discussed. For detectors with large active area a long mean free path for quasiparticles in the absorber layer is essential. We fabricated vanadium films grown epitaxially for this purpose.