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.