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 enviro nment of our experiment have yielded a substantial increase in the res olution of our Nb/Ta junctions. The junctions used in the experiment a re epitaxial base layer devices including a thick Ta absorber and have survived more than 30 cycles to low temperatures. Current experiments with a Fe-55 source have yielded an energy resolution of 68 eV at 5.8 9 keV with a quantum efficiency of 13%. Additional measurements using a higher energy Cd-109 source are also reported. We discuss how a redu ction of extrinsic and quasi-extrinsic noise sources affects the perfo rmance of the detectors and why we believe we are still not observing the intrinsic limitations of these junctions.