Takashi Yasumune

Development of a TES Microcalorimeter for Spectroscopic Measurement of LX-rays Emitted by Transuranium Elements

A phase transition edge sensor (TES) microcalorimeter was developed for the energy-dispersive measurement of LX-ray photons emitted by transuranium elements. The phase transition temperature of the TES was designed to be 200mK using a bilayer structure of Au of 120 nm thickness and Ti of 50 nm thickness. A Au layer of 5.0 mm thickness was deposited on the Au/Ti bilayer to achieve an absorption efficiency of 50% and counting rate of 100 counts per second in the detection of LX-ray photons with energy from 10 to 20 keV. The TES microcalorimeter was operated for the detection of LX-ray photons emitted by 241Am, 238Pu, and 239Pu sources. A decay time constant of 180 ms for the detection signal pulses allowed the TES microcalorimeter to operate with a counting rate higher than 100 counts per second. The achieved energy resolution was 50 eV for the full width at half maximum of a peak corresponding to a 237Np Lβ1 X-ray of 17.75 keV.

Measurement of Output Signals from an Avalanche Photodiode by Irradiating with X-rays in the Temperature Range from 150 mK to 4.2 K

We measured leakage current and gain characteristics of a reverse-type avalanche photodiode (APD). The leakage current generated below the breakdown voltage was found to be lower than 1 pA at temperatures below 200 K. Avalanche multiplication of the APD was achieved in the temperature range from 150 mK to 300 K. To characterize charge carrier properties of the APD, output signal pulses from the APD were observed by irradiating the APD with X-rays in the temperature range from 150 mK to 4.2 K. The yield of signal charge was found to abruptly change in the temperature range from 1 to 2 K, where the yield of charge at 1 K is about 50% of that at 2 K.

Development of a microcalorimeter with transition edge sensor for detection of LX rays emitted by transuranium elements.

A transition edge sensor (TES) microcalorimeter has been developed for use as an energy dispersive X-ray spectrometer. The TES microcalorimeter is a thermal detector that enables one to determine the energy of an incident photon by measuring the resultant increase in temperature. In this work, a Ti/Au TES microcalorimeter was developed to measure LX rays emitted by transuranium elements. The phase transition temperature was set at ~200 mK by using a bilayer structure composed of a 110-nm-thick Au layer and a 40-nm-thick Ti layer. An Au of 5 µm thickness was deposited on the Ti/Au bilayer to achieve an absorption efficiency of 35-80 % for the energy range of LX rays (10-25 keV). The developed TES microcalorimeter was irradiated with LX rays emitted by an (241)Am source at an operating temperature of 140 mK. An energy resolution of ~80 eV (full width at the half maximum) was obtained for L(β1)X ray of 17.75 keV.

Detection of the scintillation light emitted from direct-bandgap compound semiconductors by a Si avalanche photodiode at 150 mK

In this work, the direct-bandgap compound semiconductor materials are irradiated by α particles emitted from 241Am for the detection of scintillation light at the temperature of 150 mK. For the irradiation experiment, two disk shaped samples were fabricated from an epoxy resin mixed with the powder of PbI2 and CuI, respectively. Each disk-samples was cooled down to 150 mK by a compact liquid helium-free dilution refrigerator. A Si avalanche photodiode (APD) was employed for detecting the scintillation light emitted from the disk-sample inside the refrigerator. The detection signal current of Si APD was converted into the voltage pulses by a charge sensitive preamplifier. The voltage pulses of the scintillation light emitted from the direct-bandgap semiconductors were observed at the temperature of 150 mK.