Suppression of extrinsic resolution limiting factors in epitaxial superconducting tunnel junction detectors

Superconducting tunnel junctions have been shown to have potential as high resolution X-ray detectors. Recent reductions in the noise environment of our experiment have yielded a substantial increase in the resolution of our Nb/Ta junctions. The junctions used in the experiment are epitaxial base layer devices including a thick Ta absorber and have survived more than 30 cycles to low temperatures. Current experiments with a /sup 55/Fe source have yielded an energy resolution of 68 eV at 5.89 keV with a quantum efficiency of 13%. Additional measurements using a higher energy /sup 109/Cd source are also reported. We discuss how a reduction of extrinsic and quasi-extrinsic noise sources affects the performance of the detectors and why we believe we are still not observing the intrinsic limitations of these junctions.<>