X-ray response of Nb-based superconducting tunnel junction

Abstract
Josephson tunnel junctions are well known as low temperature electronics devices. However, they are also important as very powerful sensors. A novel class of sensors is constituted by radiation detectors based on superconducting tunnel junctions, which could lead in next future to an advanced instrumentation with an interesting applicative future. So far this area is restricted to low-temperature superconductors. Several superconducting materials have been considered. Among them, Niobium is very attractive because of its highest critical temperature T_c. We have measured detailed X-ray detection characteristics for Nb-based tunnel junction made with different fabrication processes. We will discuss the difference in the X-ray response in terms of the relevant junction's parameters, underlying the problems of the niobium as suitable material for this kind of device.