Experimental imaging diagnosis of superconducting tunnel junction x-ray detectors by low-temperature scanning synchrotron microscope

Imaging diagnosis of superconducting tunnel junction x-ray detectors has been performed by an apparatus called the low-temperature scanning synchrotron microscope (LTSSM) using an x-ray microbeam with a diameter of 5-10 mum originated from synchrotron radiation. Quasiparallel intense synchrotron radiation enables one to obtain the full two-dimensional images of junctions with dimensions of 200x200 mum(2) in about 1 h. The LTSSM results indicate that the standard quasiparticle diffusion and edge loss model for the spatial distribution of the junction response to x rays is evidently inadequate for intermediate or large junctions (with respect to a Josephson penetration depth). On this basis, it is argued that the models proposed for the signal creation and loss mechanism should be reconsidered. (C) 2000 American Institute of Physics. [S0003-6951(00)01650-8].