A Detector That Hears X-ray Light express
An X-ray photon hits the detector like a pebble dropping into still water. The water is a thin film of aluminum and manganese, cooled to near absolute zero. The impact sends a heat wave rippling across the film, and by measuring its height, you can tell how much energy the photon carried.
This is how transition-edge spectroscopy works — a technique already used to peer at distant galaxies and hunt for dark matter. But until now, such detectors for X-rays were made from two layers of different metals, which is complicated and expensive. The authors of the paper used an alloy of aluminum and manganese instead: it's easier to deposit onto a substrate, and the superconducting transition temperature is easy to tune.
Tests in a cryostat with a superconducting quantum interference device amplifier showed that the detector can distinguish two X-ray quanta if their energies differ by at least 12.1 electronvolts. At an energy of 17.48 kiloelectronvolts, that's a relative precision of 0.07 percent. No detector made from this alloy has ever achieved such performance before.
A precise X-ray spectrometer is like a very keen ear that hears not the volume but the pitch of each individual note. With it, you can determine what elements make up a substance without destroying the sample. Such instruments will be useful in materials science and astronomy alike, when you need to figure out what a distant star is shining with.
Original abstract
as written by the authors arXiv:2602.11728
The superconducting Transition-Edge Sensor (TES) is a critical technology for next-generation X-ray spectrometers, known for its exceptional energy resolution. In the last decade, TESs based on AlMn alloy films have been extensively used in several cosmic microwave background (CMB) experiments. The advantages of simple fabrication process and easily tunable critical temperature make them an alternative to bilayer TESs. However, they have rarely been applied to X-ray detection until now. We developed an annular AlMn TES for X-ray detection and tested it in a dilution refrigerator with a Superconducting Quantum Interference Device (SQUID) amplifier, achieving an Full Width at Half Maximum (FWHM) of 12.1 +- 0.3 eV at 17.48 keV. To the best of our knowledge, this is the first demonstration of an AlMn TES achieving an energy resolution below 0.1%, highlighting its potential for high-resolution X-ray detection.
The energy of 17.48 kiloelectronvolts corresponds to the X-ray emission of molybdenum — often used to calibrate detectors because this metal produces a very clean spectral line.