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A radiation sensor in the city is like a street musician: it has to hit the right notes even when fingers go numb from cold or the instrument is baked by the sun. Usually, such devices are kept in greenhouse conditions, with heating or cooling, otherwise the energy scale (which distinguishes harmless potassium in concrete from dangerous cesium) starts to lie. The new work takes a different approach: instead of fighting temperature, the program itself listens to the overall hum of radiation and tunes the strings accordingly.

The secret is that the natural background is not just noise. It carries familiar "voices": potassium-40 from granite, uranium and thorium from soil, radon that accumulates after rain, and cosmic rays. The program decomposes the measured spectrum into these components, like a conductor picking out instrument parts in an orchestra. It then compares the picture with a precomputed computer model of the sensor itself — one that accounts for how the scintillator (a substance that flashes when hit by particles) responds to different energies and how the photomultiplier tube (a device that converts flashes into current) fatigues. If the "notes" have shifted due to heat or cold, the program corrects the calibration without touching the hardware.

The tests confirmed: the sensor held its accuracy both in a climate chamber and in the field over several days under the open sky, where temperature fluctuated and rain changed the background. The method managed to separate the instrument's own drift from real changes in environmental radiation — something that used to be muddled. This approach requires no energy for heating or cooling, so networks of hundreds of cheap sensors could run for years unattended: on fences, poles, rooftops. The street musician finally has a self-tuning instrument.