Development of Transition Edge Sensor Array for Wide Energy Range Gamma-Ray Spectroscopy

We have developed a gamma-ray spectrometer based on 8-pixel superconducting transition edge sensor (TES) microcalorimeter which can detect gamma rays with energies up to 0.8 MeV. We applied 0.8 mm × 0.8 mm × 0.8 mm Sn absorbers which provide sufficient saturation energies and absorption efficiencies for gamma rays with energies more than 0.2 MeV. We used a mixed source of ¹³⁷ Cs and ²² Na which emits 32 keV X-rays, 511 keV annihilation radiations and 662 keV gamma rays. Signals from our detector were simultaneously readout using microwave multiplexing. The energy resolution of our 8-pixel TES microcalorimeters were ${\text{330}}\,{\text{ eV}} \leq \ \Delta {{E}_{\text{FWHM}}} \leq {\text{7.2}}\ \text{keV}$ , and 3 pixels showed better energy resolution than 400 eV for 662 keV gamma rays. The 511 keV annihilation peaks were $\Delta E > {\text{1}}\ \text{keV}$ , which are most likely caused by the Doppler broadening effect.