Most people are not aware of how much radiation monitoring goes on around them all the time, including in public places. Airports have sophisticated radiation detectors, for example. In 2022, devices at Heathrow flagged a package that turned out to contain a small amount of uranium. There was no risk to the public, authorities said at the time.

Mirion is one of several companies that make radiation detectors. Its products are used for defense and security applications, as well as in nuclear power plants, laboratories, and research contexts. “If there’s an incident in a nuclear plant like a fuel leak, these systems are connected to the safety system of the nuclear plant, so the nuclear plant will shut down,” explains James Cocks, chief technology officer. Area monitors suck particulate emitted by power plants onto filter paper, which can be analyzed to see whether or not there has been an uncontrolled release of radiation.

The company even makes a radiation detector designed to fit to the underside of a drone. Cocks says that, in the immediate aftermath of Fukushima, such was the need to collect data on radiation that someone drove around on a motorbike with a radiation detector. Drones would, today, offer a safer way of gathering such information, he suggests.

But Mirion also makes handheld detectors that can be carried by personnel keeping an eye on major sports events, for example. And these can distinguish between different types of radiation. You want to be able to tell, for example, whether your higher-than-normal readings are coming from a dirty bomb—or just someone who recently had medical treatment involving a radioisotope. “We can identify whether it’s naturally occurring background radiation, whether it’s a medical radioisotope, or whether it’s a fission product,” says Cocks.

And so one legacy of the Chornobyl and Fukushima disasters is that we now have hugely upgraded radiation-monitoring systems dotted around the world. There has been a marked increase in efforts to track radiation in the wake of those accidents, says Kearfott.

Bonner acknowledges that some people experience anxiety regarding radiation—now and again, a volunteer would build a Safecast detector, switch it on and “freak out” when it began detecting activity, he says. However, it is important to show how pervasive, and variable, background radiation really is, he says: “We absolutely believe that it’s reassuring to let people know what’s going on.”