Rikkyo University

OBJECTIVE.

Researchers including Associate Professor Shinya Yamada and Assistant Professor Yuto Ichinohe of the Rikkyo University College of Science, Tomoya Uruga, Kiyofumi Nitta, and Oki Sekizawa of the Japan Synchrotron Radiation Research Institute (JASRI), and Professor Yoshio Takahashi of the University of Tokyo Graduate School of Science, together with an international team of experts promoting the use of transition-edge sensors (TES)(*1), conducted the world's first successful fluorescence X-ray absorption fine structure (XAFS)(*3) analysis of environmental samples by introducing a TES into the beamline BL37XU at the large synchrotron radiation facility SPring-8(*2). This achievement paves the way for applications in ultramicroanalysis and emission spectroscopy.

The study was published on the website of the U.S. journal "Review of Scientific Instruments" on January 13, 2021 (2 a.m. Japan time). Through the study, it is now possible to use fluorescence XAFS to conduct high-sensitivity state analysis of ultratrace elements in terrestrial, environmental, and extraterrestrial substances or biological samples. Developments are also anticipated in high-precision emission spectroscopy methods such high-energy-resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES). Research on TES is underway on instrument development and applicability in various fields, such as cosmic X-ray observations and atomic, molecular, and nuclear physics. This represents the first step toward nondestructive analysis of the asteroid materials brought back by Hayabusa2 and extraterrestrial samples obtained in future sample return programs.

Research Results

In July 2019, they conducted the first demonstration by using a TES detector (manufactured by NIST in the United States) and a semiconductor detector (silicon drift detector: SDD) in the BL37XU beamline at SPring-8. Figure 1 compares the energy spectra measured in a standard sample for X-ray spectroscopy. X-ray fluorescence from elements that cannot be extracted by SDD were successfully analyzed, and X-ray spectra over a wide energy range were obtained all at once, which is difficult to do with analyzing crystals. They were also the first to apply fluorescence XAFS using a TES to analyze the chemical states of trace elements in environmental samples. This makes it possible to perform analyses that have previously proved difficult, such of the chemical states of trace amounts of iron in marine aerosols associated with climate change, and of lead coexisting with arsenic, which is important for analyzing the behavior of hazardous substances. This greatly expands the scope of applications for fluorescence XAFS.
The study was published on the website of the U.S. journal "Review of Scientific Instruments" on January 13, 2021 (2 a.m. Japan time).
“Broadband high-energy resolution hard x-ray spectroscopy using transition edge sensors at SPring-8”

Figure 1: (Left) X-ray spectra of the standard sample obtained at Spring-8. (Right) Photograph of the outside of the TES during the experiment.　S. Yamada et al., Rev. Sci. Instrum. 91 (2020), doi: 10.1063/5.0020642

Figure 2: Principles of TES operation and TES pixel diagram

(*4)
TES is a detector that utilizes the steep resistance-temperature characteristics near the phase transition temperature of superconductivity and normal conduction. Figure 2 shows how it operates. When X-rays hit the heat-absorbing part of the detector, the temperature of the TES rises, along with its resistance.
By detecting changes in the current flowing through the circuit, the energy of the irradiated X-rays can be estimated. Because the change in resistance during this is extremely large in superconductors near the phase transition temperature, the energy estimates have good accuracy.

(*5)
High-energy-resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) is a method of fluorescence XAFS for finely separating the wavelengths of specific X-ray fluorescence (spectroscopically with high energy resolution). In the past crystals were used for spectroscopy, but a drawback of this is that much useful information is discarded. Using a non-dispersive spectroscope such as TES could increase the efficiency of measurements.