A Sensitive Thermometer for X-rays express
An X-ray beam is a stream of tiny packets of energy, photons. Ordinary detectors count them but don't distinguish shades: two photons with close energies look the same to them. The new device works like a sensitive thermometer: it catches each photon and measures how much it warms a thin film. From the warming, you can tell exactly how much energy the photon brought. A difference of a few electronvolts is like telling a grain of sand from two grains on your palm.
Tests were conducted at the SPring-8 synchrotron — a huge ring where electrons are accelerated to nearly the speed of light, and they emit bright X-rays. The detector, with 240 pixels, simultaneously monitored the beam and distinguished photons with an accuracy of 4 electronvolts at an energy of 6 thousand. That's like hearing a whisper in a noisy hall. The device withstood a flux of 2 thousand photons per second across all pixels, maintaining an accuracy of 5 electronvolts.
Such sensitivity opens new doors. Previously, the arsenic line and the lead line in the X-ray spectrum merged into a single hump: their energies are almost identical. Now they appear as two separate peaks, and you can track lead without interference from arsenic. This is important for analyzing soil, ore, or even dust particles in the air.
The device is a first step toward having such precise detectors at all hard X-ray synchrotrons. Then chemists, geologists, and ecologists will be able to look into the composition of matter as easily as we distinguish colors in a rainbow.
Original abstract
as written by the authors arXiv:2604.21846
We have succeeded in operating a transition-edge sensor (TES) spectrometer and evaluating its performance at the SPring-8 synchrotron X-ray light source. The TES spectrometer consists of a 240 pixel National Institute of Standards and Technology (NIST) TES system, and 220 pixels are operated simultaneously with an energy resolution of $$4$$~eV at 6~keV at a rate of about 1~c/s/pixel. The tolerance for high count rates is evaluated in terms of energy resolution and live time fraction, leading to an empirical compromise of about 2 x 10^3 c/s/all pixels with an energy resolution of 5 eV at 6 keV. By utilizing the TES's wide-band spectroscopic capability, simultaneous multi-element analysis is demonstrated for a standard sample. We conducted X-ray absorption near-edge structure (XANES) analysis in fluorescence mode using the TES spectrometer. The excellent energy resolution of the TES enabled us to detect weak fluorescence lines from dilute samples and trace elements that have previously been difficult to resolve due to the nearly overlapping emission lines of other dominant elements. The neighboring lines of As K alpha and Pb L alpha2 of the standard sample were clearly resolved and the XANES of Pb L alpha2 was obtained. Moreover, the X-ray spectrum from the small amount of Fe in aerosols was distinguished from the spectrum of a blank target, which helps us to understand the targets and the environment. These results are the first important step for the application of high resolution TES-based spectroscopy at hard X-ray synchrotron facilities.
The energy of an X-ray photon at 6 keV is billions of times greater than the energy of visible light, yet the detector senses a difference of just 4 electronvolts, like a market scale noticing a feather falling onto a truck.