Superconducting tunnel junctions for use as energy resolving X-ray detectors

The response of Nb-Al-Al/sub 2/O/sub 3/-Al-Nb superconductor-insulator-superconductor (SIS) tunnel junctions to pulsed 650-nm radiation was measured. The rise in the voltage developed across the junction increases linearly for the duration of the applied pulse. The decay time of 300 mu s is an intrinsic property of the junction. The response of the junction varies linearly with incident energy over the range 35 to 200 eV/ mu m/sup 2/. Comparison with the junction response caused by higher energy particles should give insight into the microscopic details of the extremely nonequilibrium pair breaking.