ENERGY RESOLUTION AND HIGH COUNT RATE PERFORMANCE OF SUPERCONDUCTING TUNNEL JUNCTION X-RAY SPECTROMETERS

We present experimental results obtained with a cryogenically cooled, high-resolution x-ray spectrometer based on a 141 mu m x 141 mu m Nb-A l-A1(2)O(3)-Al-Nb superconducting tunnel junction (STJ) detector in a demonstration experiment. Using monochromatized synchrotron radiation we studied the energy resolution of this energy-dispersive spectromete r for soft x rays with energies between 70 and 700 eV and investigated its performance at count rates up to nearly 60 000 cps. At count rate s of several 100 cps we achieved an energy resolution of 5.9 eV (FWHM) and an electronic noise of 4.5 eV for 277 eV x rays (the energy corre sponding to C K). Increasing the count rate, the resolution 277 eV rem ained below 10 eV for count rates up to similar to 10 000 cps and then degraded to 13 eV at 23 000 cps and 20 eV at 50 000 cps. These result s were achieved using a commercially available spectroscopy amplifier with a baseline restorer. No pile-up rejection was applied in these me asurements. Our results show that STJ detectors can operate at count r ates approaching those of semiconductor detectors while still providin g a significantly better energy resolution for soft x rays. Thus STJ d etectors may prove very useful in microanalysis, synchrotron x-ray flu orescence (XRF) applications, and XRF analysis of light elements (K li nes) and transition elements (L lines). (C) 1998 American Institute of Physics.