Development of Innovative X-ray Detectors - The Quest for Ultra Energy Resolution in X-ray Spectroscopic Measurements.


TES microcalorimeter for the detection
of LX-ray photons emitted by
transuranium elements

When a material is irradiated with radiation beams such as synchrotron radiation or electron beams, characteristic x-rays are emitted by elements that constitute the material. This "x-ray spectroscopic analysis" is a method used to identify and quantify the elements by analyzing the energy and the intensity of the characteristic x-rays. An x-ray detector with superior energy resolution is vital in x-ray spectroscopic analysis. In our laboratory, innovative x-ray detectors are developed by utilizing superconducting devices, for the purpose of establishing x-ray spectroscopy with ultra energy resolution.

The energy resolution of the x-ray detector contributes to the accuracy of x-ray spectroscopic analysis. Usually, Si semiconductor detectors are used in x-ray spectroscopic analysis. However, the energy resolution of the Si semiconductor detector has reached its theoretical limit. For example, we cannot detect x-rays of 6 keV with an energy resolution any better than 130 eV. To surpass the energy resolution of semiconductor x-ray detectors, many kinds of cryogenic x-ray detectors have been devised by using the physical properties of materials in low temperature regions for superconductivity, ultra-small specific heat and so on. Since the specific heat of most solid materials decreases with the temperature, the energy of the incidental x-ray photons is converted to the higher temperature in the energy absorber, in the low temperature region below 1 K. This principle applied with an x-ray detector is called a microcalorimeter. The microcalorimeter consists of an energy absorber and a sensitive thermometer, the latter being an important component of the microcalorimeter. The transition edge sensor (TES) utilizes the steep change in the electrical resistance of the superconducting thin film in the phase transition temperatures. TES microcalorimeters have demonstrated superior energy resolution below 10 eV of FWHM value in detecting x-ray photons with the energy of several keV. We are working on the research and development of TES microcalorimeters for spectroscopic measurements of LX-ray photons emitted by transuranium elements, and for an innovative energy dispersive spectroscopy system equipped with several types of electron microscopes.

Applied Nuclear Physics,
Department of Applied Quantum Physics and Nuclear Engineering,
Faculty of Engineering, Kyushu University
Professor Kenji Ishibashi
Associate Professor Keisuke Maehata
Associate Professor Naoko Iyomoto
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