Some aspects of superconductive junction radiation detectors

The potential of superconducting devices as radiation detectors spans over a large variety of applications such as particle detections, X-my astronomy, dark matter search, mass spectrometry. In particular, Superconductive Tunnel Junctions (STJ) offer great possibilities for high energy resolution and fast response combined with an excellent radiation hardness. In the frame of our research activity all refractory Nb junctions with low leakage current have been realized by different preparation processes. New experiments on injection-detection experiments with a discussion of the underlying nonequilibrium superconductivity involved are reported. Interesting results have been obtained also on the delicate issue of junction geometry which plays a fundamental role in determining the detector performances. The required high transparency of the tunneling barrier for a higher charge collection implies the occurrence of Josephson effect. This, in turn, represents a drawback for the bias requirements of the detector which has to operate in the quasiparticle tunneling regime when devoted to energy spectroscopy. Suppression of zero-voltage current and current steps at a finite voltage can be realized by a proper junction geometry. Experimental results are reported which show a great potential for further improvements of junction detectors.