Response of a superconducting transition-edge sensor microcalorimeter with a mushroom-shaped absorber to L X-rays emitted by transuranium elements

A four-pixel-array superconducting transition-edge sensor (TES) microcalorimeter with a mushroom-shaped absorber was fabricated for the energy dispersive spectroscopy performed on a transmission electron microscope. The TES consists of a bilayer of Au/Ti with either a 50-nm or 120-nm thickness. The absorber of 5.0/im thick is made from a Au layer and its stem is deposited in the center of the TES surface. A Ta₂O₅ insulating layer of 100-nm thickness is inserted between the overhang region of the absorber and the TES surface. A selected pixel of the TES microcalorimeter was operated for the detection of Np L X-rays emitted from an ²⁴¹Am source. A response of the TES microcalorimeter to L X-rays was obtained by analyzing detection signal pulses with using the optimal filter method. An energy resolution was obtained to be 33 eV of the full width at half maximum value at 17.751 keV of Np L_β1 considering its natural width of 13.4 eV. Response to L X-rays emitted from a mixture source of ²³⁸Pu, ²³⁹Pu and ²⁴¹Am was obtained by operating the selected pixel of the TES microcalorimeter. Major L X-ray peaks of progeny elements of α decay of Pu and Am isotopes were clearly identified in the obtained energy spectrum. The experimental results demonstrated the separation of ²⁴¹Am and plutonium isotopes by L X-ray spectroscopy.