Thermal Conductance of Thick-Membrane TES Microcalorimeters for Several-MeV Gamma Rays

We developed transition-edge sensor (TES) microcalorimeters to measure gamma rays with up to a few megaelectron volts. Our TES devices have a thick silicon membrane that supports a large absorber. We fabricated devices with different sizes of the TES and membranes to study the thermal conductance of the membrane. We found that the thermal conductance G of the membrane is less dependent on the distance between the TES and heat bath because heat is mainly transported by ballistic phonons in the thick membrane. In addition, gamma-ray irradiation experiments were conducted using a TES device with a large bismuth absorber (1 mm × 1 mm × 1 mm) and a thick membrane (6 μm); the energy response of the device was found to be largely linear.