A graphene ribbon nine atoms wide is like a track where electrons race, as water rushes down a narrow trough. Gamma radiation is a stream of particles with enormous energy, capable of punching through metal and plastic. When such a stream hits the ribbon, it doesn't break it: it just lightly scratches the surface, leaving extra oxygen atoms behind.
Scientists assembled a transistor from such a ribbon and exposed it to gamma rays. After irradiation, the ribbon's structure barely changed, as revealed by a spectrometer, a device that 'sees' atomic vibrations. But the current through the ribbon dropped noticeably. Electrons started getting stuck on the imperfections more often, like water catching on the rough spots of a trough.
This sensitivity is not a flaw but a useful feature. If the ribbon changes conductivity in response to radiation, it can be used as a sensor. Such a sensor could fit on a chip and monitor radiation right inside a spacecraft or next to a nuclear reactor.
Gamma rays are the most energetic form of light. A single gamma ray carries thousands of times more energy than visible light and can pass through several centimeters of lead.