In a gas chamber used to register particles, electrons behave like fast couriers: they race off in all directions and lose formation. Negative ions, by contrast, are heavy porters who walk at a steady pace and don't scatter. For detectors hunting dark matter, that kind of tidiness matters a lot: the more even a particle's trail, the more precisely you can tell where it came from.

Previously, to get negative ions, special substances that capture electrons were added to the gas. But those additives weakened the signal and could be dangerous. The authors of the new work tried something different: they took pure CF4 gas and simply raised the electric field. The electrons accelerated so hard that they tore gas molecules apart, and an electron stuck to one of the fragments. That's how negative ions were born, with no additives at all.

Scientists counted these ions one by one using fast photomultipliers, devices that can see faint flashes of light. Each ion produced its own signal, and that made it possible to measure particle energies even more precisely than the usual method. Now it's possible to build large detectors that resolve fine details of a track without hazardous gas additives.