Superconducting Tunnel Junction Detectors - Analysis of the Linear Regime

A theoretical analysis of the linear regime in a superconducting tunnel junction (STJ) has been carried out on the basis of a kinetic approach to the non-equilibrium superconductivity induced in the detector by an X-ray. A solution of the diffusive equation of the quasi-particles has been obtained assuming very slow recombination processes and an equilibrium 2-DELTA-phonon distribution. Under these conditions, the response of the detector is linear, that is the charge collected by the detector itself is proportional to the energy released. A relation between this released energy and the collected charge has also been obtained, thus achieving an expression of the mean energy-epsilon per excess quasi-particle. A comparison with some experimental results taken from current literature has been also reported