Superconducting Transition Edge Sensor for Gamma-Ray Spectroscopy

Abstract

SUMMARY Superconducting Transition edge sensor (TES) coupled with a heavy metal absorber is a promising microcalorimeter for Gammaray (γ-ray) spectroscopy with ultra-high energy resolution and high detection efficiency. It is very useful for the non-destructed inspection of the nuclide materials. High resolving power of γ-ray peaks can precisely identify multiple nuclides such as Plutonium (Pu) and Actinides with high efficiency and safety. For this purpose, we have developed the TES coupled with a tin absorber. We suggest the new device structure using the gold bump post which connects a tin absorber to the thermometer of the superconducting Ir/Au bilayer. High thermal conductivity of the gold bump post realized strong thermal coupling between the thermometer and the γ-ray absorber, and it brought the benefit of large pulse height and fast decay time. Our TES achieved the good energy resolution of 84 eV FWHM at 59.5 keV. Using this TES device, we also succeeded to demonstrate the nuclear material measurements. In the measurement of a Pu sample, we detected the sharp γ-ray peaks from 239 Pu and 240 Pu, and of a Fission Products (FP) sample, we observed fluorescence X-ray peaks emitted by the elements contained in FP. The TES could resolve the fine structures of each fluorescence X-ray line like K α1 and K α2 . In addition to that, we developed the TES coupled with tantalum absorber, which is expected to have higher absorption efficiency for γ-rays. This device reported the best energy resolution of 465 eV at 662 keV.

511-CAM mission: a pointed 511 keV gamma-ray telescope with a focal plane detector made of stacked transition edge sensor microcalorimeter arrays

“…Whereas different absorber materials have been tested extensively for x-ray microcalorimeters, fewer studies have been completed for γ-ray microcalorimeters. 50,51 Given that the performance of γ-ray microcalorimeters is limited by phonon noise that scales with the heat capacitance of the absorbers, the selection of an absorber material with low specific heat capacity is particularly important for these γ-ray detectors.…”

“…This factor, along with vibrational noise from the dilution refrigerator, potentially contributes to the slightly worse-than-expected energy resolution. 51 The motivation for using Bi 0.57 Sn 0.43 is to make an absorber material that combines the high stopping power of Bi with the low heat capacitance of a superconductor that transitions at a higher, easier temperature. While the transition temperature of Sn at ambient pressures is 3.72 K, that of Bi is estimated to be <1.3 mK; 58,59 Prakash et al reported 0.53 mK.…”

The 511-CAM Mission: A Pointed 511 keV Gamma-Ray Telescope with a Focal Plane Detector Made of Stacked Transition Edge Sensor Microcalorimeter Arrays

“…Whereas different absorber materials have been tested extensively for X-ray micro-calorimeters, fewer studies have been completed for γ-ray microcalorimeters. 52,53 Given that γ-ray microcalorimeters require macroscopic absorbers to stop the γ-rays, a low heat capacitance is relatively important for these detectors. We consider four materials as options for the 511-CAM absorbers: Sn (the material currently used on the SLEDGEHAMMER detectors), Ta, Bi, or a Bi 0.57 -Sn 0.43 alloy (see Table 1).…”

“…Indeed, Ohno et al already demonstrated that a microcalorimeter with small 0.5×0.5×0.3 mm 3 Ta absorbers achieves a 445 eV FWHM energy resolution at 662 keV, and thus solidly outperforms HPGe detectors. 53 We utilized a 511 keV near-field source whose profile is given by the concentrated radial beam on the focal plane. An effective observation time of 1 Ms has been assumed for a balloon flight, and the flux was modified for the effects of atmospheric absorption.…”

Reliable packaging of Josephson voltage standard circuit for cryocooler operation

“…While varnish or silver paste are used to mount a chip with low dissipation power such as superconducting sensors and so on [24,25], the use of them resulted in a significant temperature increase in the voltage standard chip due to large dissipation power. Thus, a silicon chip is solderbonded to a copper substrate to achieve good thermal contact between the chip and a cryocooler.…”