High-resolution hard X-ray and gamma-ray spectrometers based on superconducting absorbers coupled to superconducting transition edge sensors

We are developing detectors based on bulk superconducting absorbers coupled to superconducting transition edge sensors (TES) for high-resolution spectroscopy of hard X-rays and soft gamma-rays. We have achieved an energy resolution of 70 eV FWHM at 60 keV using a 1×1×0.25 mm³ Sn absorber coupled to a Mo/Cu multilayer TES with a transition temperature of 100 mK. The response of this detector is compared with a simple model using only material properties data and characteristics derived from IV-measurements. We have also manufactured detectors using superconducting absorbers with a higher stopping power, such as Pb and Ta. We present our first measurements of these detectors, including the thermalization characteristics of the bulk superconducting absorbers. The differences in performance between the detectors are discussed and an outline of the future direction of our detector development efforts is given.