A monolithic superconducting micro-calorimeter for X-ray detection

A cryogenic micro-calorimeter detector using a small bulk iridium single crystal as both absorber and as transition edge thermometer has been prepared. The detector is voltage biased, and the current through it is measured with a DC-SQUID. In this mode of operation an improvement of the detector performance by the electrothermal feedback is expected. In fact, we observed a stabilization of the working temperature due to this effect. By irradiating the micro-calorimeter with an 241Am X-ray and γ-ray source an RMS energy resolution of σ=150 eV for 14 keV X-rays and σ=250 eV for 60 keV γ-rays was observed.