Deep inside an underground laboratory, a room-sized detector waits for an event that might happen once in a hundred million billion years. That event is neutrinoless double beta decay — a process that would break one of physics' fundamental laws. To catch it, you need perfect silence: not a single stray radioactive atom in the detector's materials.

Ordinary resistors, small components that control electrical signals, often contain impurities that are themselves radioactive. For the nEXO experiment, scientists made resistors from amorphous silicon — the same material used in solar panels, but without a crystalline lattice. They lightly "seasoned" it with other elements so it conducts electricity just enough.

The prototypes survived cold down to minus 100 degrees Celsius, voltages in the thousands of volts, and remained clean enough. What's more, they reflect ultraviolet light well — light that is generated inside the detector. It's like a mirror in a dark room: every photon must stay inside so the signal isn't lost.

Now the technology will be refined so these resistors can be used not only in nEXO but also in other instruments where sterile cleanliness is crucial.