Transition Edge Sensor Microcalorimeter with Bismuth Absorber for Gamma-Ray Measurement

We developed a transition edge sensor (TES) microcalorimeter to measure high-energy gamma-rays in the range of up to several MeV. We performed gamma-ray irradiation experiments using this TES microcalorimeter fabricated with a cubic bismuth cut out (1 × 1 × 0.7 mm). As a result, we successfully achieved an energy resolution of 0.92 keV for 662-keV gamma rays (137Cs) and 0.97 keV for 1332-keV gamma rays (60Co). In addition, we investigated methods to reduce low-frequency noise based on the results obtained by comparing the count rates of pulses with different decay time.