Superconducting high energy resolution gamma-ray spectrometers

In x-ray and gamma-ray spectroscopy, it is desirable to have detectors with high energy resolution and high absorption efficiency. We have developed ultra-sensitive microcalorimeters which use high-purity polycrystalline bulk materials as absorbers and superconducting transition edge sensor (TES) as thermometers. We have demonstrated the use of these detectors in high energy resolution gamma-ray spectroscopy. We measured an energy resolution of 70 eV (FWHM) for 60 keV incident gamma-rays using electrothermal feedback. This result is among the best measurements of its kind to date. We have also operated these microcalorimeters with an external active feedback bias to linearize the response of the detector and to extend its detection energy range.{09}We present x-ray and gamma-ray results from several different implementations of this detector design. We also make comparisons with variations in the detector geometry and discuss detector performance. This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.