High Energy Gamma-Ray Spectroscopy Using Transition-Edge Sensor With a Superconducting Bulk Tantalum Absorber

We are developing transition edge sensor with a superconducting high-Z metal bulk absorber for high energy resolution spectroscopy of hard X-ray and gamma-ray within 100 keV ~ 1 MeV. We applied a bulk tantalum absorber for it has low heat capacity and high absorption efficiency to high energy photons. As a result of an experiment using gamma-ray from ¹³⁷Cs, an energy resolution that is better than that of Ge semiconductor detector was achieved at 662 keV. In addition, we demonstrated more than three times higher absorption efficiency to 662 keV photons compared to Sn absorber TES as previously reported elsewhere. From our rough calculation, it is estimated that the heat capacity of tantalum is increased than theory and that may be the limit factor of the energy resolution.