Development of Bulk Superconducting-Absorber Coupled Transition-Edge Sensor Detectors for Positron Annihilation Spectroscopy

We present a high-resolution bulk tin-absorber coupled transition-edge sensor microcalorimeter to be applied for positron annihilation spectroscopy at 511 keV. We demonstrate an energy resolution of 526 eV at 662 keV from a ¹³⁷Cs source. This is the best energy resolution reported so far for any available detector at this photon energy. Further works are ongoing to reduce the mechanical vibrations of the cryogenic system in order to optimize the energy resolution of the detector.