Effects of fluxoid trapping on signal creation in superconducting tunnel junction X-ray detectors

Trapping of fluxoid quanta influences the performance of tunnel junction X- ray detectors. It has been found that the trapped vortices corresponding to a terrestrial magnetic held are enough for charge output and quasiparticle losstime to decrease by factors of two and three, respectively. This resul t leads to an effective vortex radius of R-eff = 3 xi, which is in a good a greement with a Golubov's calculation. Magnetic images by a scanning SQUID microscope show that the trapping takes place at junction edges or inside t he junction at random. The random trapping may cause an instability of the detector performance. On average, the cooling in a perpendicular magnetic f ield results in the trapping of the corresponding vortex density, that is B /Phi(0). (C) 2000 Elsevier Science B.V. All rights reserved.