In the labyrinthine basements of Bristol University’s physics department, nuclear physicist Dr David Megson-Smith is telling me about how much he doesn’t like wearing a hazmat suit when he goes to Chernobyl.
“Once you get in the field, you just start sweating,” he says. “And suddenly, you’re far less aware of your surroundings. You’re less safe.”
Standing next to him, his colleague Dr Yannick Verbelen adds: “You’re tucked into plastic and you’re transpiring. You’re moving, and it’s already a stressful environment because there is radiation around and you don’t want to linger too much.”
We’re experiencing this on a minute scale as we talk: although in thin blue lab coats rather than hazmats, the warmth emanating from the large machines pumping around us makes this feeling easier to imagine. Some of the machines even contain tiny specks of radioactive material brought back from nuclear sites.
Specialising in disaster response and clean-up operations, it’s here that Megson-Smith and Verbelen conduct what they call ‘nuclear forensics’. This involves returning from a disaster zone with radioactive samples as small as a grain of sand to analyse in their lab. With these, they hope to extract information like whether the particle came from fallout or a nuclear fusion reactor.
But their current focus is on improving analysis while in the disaster zones themselves. How? By making nuclear caves glow a luminous yellow-green, of course – and using a mysterious new contraption they call the ‘Dark Star’.
The duo achieved this goal in March, when they travelled with their team to the abandoned Cold-War era uranium mines of the deserts of Arizona, USA. Operation Dark Star aimed to detect and reveal uranium with an ultraviolet (UV) light camera – rather than through the ticking Geiger counters you’ve seen in films and video games.
Why? A visual sensor will allow scientists to conduct future radioactivity monitoring from a safe distance – without risking irradiation to themselves.
Nuclear forensics’ autonomous detective
Verbelen, Megson-Smith and their small project team are internationally recognised for using robotics to track the spread and risk of radioactive incidents. (When, in January 2023, a truck travelling across Western Australia dropped a radioactive capsule strong enough to kill someone in a few hours if touched, the team was kept on standby to find it. The capsule was the size of your smallest fingernail.)
Their newest invention, Dark Star is the world's most powerful mobile UV fluorescence imaging device: 'Star' because of its incredibly intense light, but 'dark' because this light is not visible to the human eye.
They’ve designed it to be autonomous: it calibrates itself to the setting, illuminates the radioactivity, and records the data – all while the scientists observe from a safe distance.
Geiger counters, meanwhile, often have to take measurements at close quarters. They also have no directionality, Megson-Smith says, while the Dark Star reveals radiation everywhere its light touches.
So how does it work? The Dark Star is essentially a very sophisticated sensor system – not unlike an expensive digital camera, but one that takes pictures of things usually invisible to the human eye.
“In contrast to what we've been made to believe in The Simpsons, uranium doesn't actually glow in the dark. It's just a heavy metal not too dissimilar to lead – albeit slightly radioactive,” says Verbelen.
“However, when uranium is exposed to water and air in the natural environment, it ‘rusts’ and forms uranium oxides,” Verbelen continues. “When those oxides combine with other elements, they form minerals that do glow in the dark, with a little bit of 'help'.”
This ‘help’ is what the scientists call stimulated fluorescence: when the uranium absorbs another type of radiation – in this case, UV light – and then emits light in response, which we perceive as a glow.
But it’s not as straightforward as shining a UV lamp at it. Verbelen says: “To make uranium minerals glow by fluorescence, a UV light source is needed that is orders of magnitude more powerful than the one used to check for counterfeited money in a supermarket, and there are no power sockets in abandoned uranium mines to plug them into, either!
“So how do we solve this problem? That's where the Dark Star comes in.”
The future of nuclear safety is sunglasses
The fluorescence it produces is incredibly bright, lighting up the cave in an eery glow.
But their invention poses its own dangers. According to the researchers, direct exposure to the Dark Star would give you the equivalent of a sunburn to skin. That's why they don't stand directly in front of it – but even a tiny glimmer of the scattered (reflected) UV light in the caves is powerful enough to cause eye damage.
So, while there were no hazmats down there, the researchers had to wear sunglasses for protection – despite being there in the middle of the night and deep underground. “If anyone had seen us, without a doubt, they would have assumed we were crazy,” says Verbelen.
Next, they plan to take Dark Star back to the caves – but this time putting it on walking robots and drones. The Arizona mines are a good place to test the equipment for use in harsher environments like Chernobyl and Fukushima, “where it definitely would not be safe to stand around,” Verbelen laughs.
Hazmats may still be the uniform for Chernobyl field researchers for years to come, but increasing the distance between themselves and the radiation will form another (though slightly less sweaty) layer of protection.
Radiation is not something to be scared of, the pair emphasise seriously. They’re exposed to more radiation flying over the North Pole during each trip to the USA than down in the uranium mines.
Equally, Megson-Smith says, “If you’re not scared, you’re probably not being sensible”.
“But you don’t have to be scared if you know what you’re doing," Verbelen adds. “That’s why Dark Star is so important – we can now see materials from a distance of 3-10 metres (10-33ft) away. We don’t have to stand next to the radioactive material anymore.”
About our experts
Dr Yannick Verbelen is a Senior Research Associate in the University of Bristol’s Interface Analysis Centre. His published research includes the radiological mapping of Chernobyl, published in Frontiers in Robotics and AI, and an analysis of Japan’s Fukushima accident, published in journal Scientific Data.
Dr David Megson-Smith is a Research Fellow in the University of Bristol’s Interface Analysis Centre. He also leads Hot Robotics, which loans robotic machinery for research in radioactive environments. His research has been published in the Journal of Radiological Protection, Journal of Field Robotics, and Frontiers in Robotics and AI.
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