A tiny radioactive capsule, smaller than a 10-cent coin and lost on a stretch of highway in outback Western Australia, has miraculously been found.
The caesium-137 capsule, measuring just 8 millimetres long, was lost between Perth and a Rio Tinto mine site in the Pilbara.
It sparked a frantic search along the 1,400-kilometre highway where specialist teams held radiation detection equipment while travelling the road at 70kph.
It was like trying to find a needle in a haystack.
But on day six of the search, authorities found the capsule two metres from the side of the road just outside the town of Newman.
As biophysicist Ivan Kempson from the University of South Australia points out, this situation was a best-case scenario.
But what happens when a radioactive source isn't found in time?
What was the risk of the lost capsule?
When talking about radiation and risk, Dr Kempson said it's important to remember we're exposed to radiation all the time, such as cosmic rays from space or radioactive decay in the minerals around us.
Everything from an X-ray to a granite benchtop to bananas in a fruit bowl emit low levels of radiation that humans are biologically well equipped to deal with, and pose little risk.
But Dr Kempson said the risk increases when radiation becomes higher than that background level.
On average, Australians are exposed to about 1.5 millisievert (mSv) of background radiation a year.
Where the risk increases will depend on the radiation dose of the source, as well as the exposure time and proximity to the source.
There are also certain materials that are highly radioactive, such as uranium, plutonium and — in the case of the WA capsule — caesium-137.
Caesium is a metal that can come in radioactive forms, and is used in various industries. Caesium-137 is one of the radioactive forms, and its potency depends on how big a piece you're dealing with.
In the case of the WA capsule, the state's chief health officer and chair of the Radiological Council Andrew Robertson said standing a metre from the source for an hour would have been the equivalent of receiving the radiation dose of 10 X-rays.
"To be at risk of radiation exposure, you need to be close to the source for a period of time," Dr Robertson said.
Dr Kempson said while the capsule lost in WA was "very, very tiny" it was "still emitting quite a bit of radiation".
"If you were just several metres away — 10, 20 metres — from this capsule, that'd be very little risk," he said.
"If you were holding it, even if it was for several minutes, then it's quite similar to receiving X-rays for a medical diagnostic.
"The real concern is if somebody picked it up and they had it in their pocket for many hours, and was very close to it for very prolonged durations."
So what would happen if you put it in your pocket?
Any damage would depend on the potency of the radioactive source.
But if the level was high enough, the exposure of having a radioactive source in your pocket could lead to leg amputation, or even death.
This is what happened to a 37-year-old Peruvian welder at the Yanango hydroelectric power plant about 300km east of Lima.
On the morning of February 20, 1999, the welder and his assistant arrived at the plan to carry out repairs on a pipe.
Later that morning, a radiographer and his assistant arrived to install a camera housing a radioactive source close to where the pipe repairs were being carried out.
At some point during the day, the unshielded radioactive source became detached from the camera.
Noticing it, the welder picked it up and put it in his back pocket where it remained for at least five hours.
When he returned home from work that night he complained of a pain on the back of his thigh.
He took off his pants with the source still in the pocket — leaving them on the floor — and went to check his leg.
The man had developed a blistering lesion on the back of his right thigh.
The man's wife had been sitting on the floor on top of the pants, breastfeeding their child.
It wasn't until the following day they realised the small item in the pants pocket was radioactive.
Though her exposure was only brief, the man's wife developed lesions on her lower back. But her condition was nowhere near as bad as her husband's would become.
Over the following days the man became seriously ill, experiencing muscle swelling, peeling skin, intense pain, numbness, hypersensitivity and rapid weight loss.
A month later the blister had grown to an ulcer measuring 10 centimetres in diameter.
He also developed blisters on his fingers and further lesions on his buttocks and genitals, plus constant fevers.
He needed multiple blood transfusions.
The initial lesion eventually became infected and grew to cover a third of his right thigh, affecting his sciatic nerve which caused him chronic pain and suffering.
With extensive loss of tissue in his right leg, and facing possible death, the man was taken to France where doctors performed an amputation, covering the top of the thigh with a skin graft.
Dr Kempson said the radioactive material in the Yanango case, iridium-192, was roughly 1,000 times more radioactive than the WA capsule, but also noted that the type of radiation emitted from the material was different.
While caesium-137 emits high-energy photons and highly energetic electrons, iridium-192 only emits high-energy photons.
"This difference means that the [caesium-137] would lead to more damage to the skin whereas the damage from [iridium-192] can be spread out deeper into tissue," he said.
What happens if a radioactive source remains lost?
The search for the lost capsule in WA triggered an immediate and highly publicised search, but not all responses are as rigorous.
In the 1970s, a small radioactive capsule with a caesium-137 source — originally part of a radiation level gauge — was lost in the Karansky quarry in Soviet Ukraine's Donetsk region.
The search for the capsule was eventually abandoned and the gravel from the quarry was used in the construction of an apartment building in Kramatorsk.
In 1981, a year after construction, an 18-year-old girl who lived in apartment number 85 died of leukaemia.
A year later, her 16-year-old brother died of the same illness, followed by their mother.
Doctors believed the three deaths were a result of some genetic predisposition, but when a new family moved into the apartment and their son also died of leukaemia, his father pushed for an investigation.
Specialists arrived at the apartment with a dosimeter and discovered sky-high radiation levels.
A powerful gamma radiation was coming from the wall where, after further testing, authorities found the capsule containing caesium-137.
Dr Kempson said this source may have been more potent than the capsule lost in WA.
"If it was much bigger, it would be giving proportionally more radiation," he said.
Why the situation in WA is a best-case scenario
Dr Kempson said the radiological events in Peru and Ukraine were very different to the situation in WA, which he said was a best-case scenario.
"Radioactive material is so highly regulated and controlled in how it's managed and how it's disposed of that we are seeing the transparency in this event," he said.
"Because of those strict regulations, we promptly know it's not where it should be, so it's good to see that these strict regulations are really coming into effect.
"It's fantastic to have the media attention around this to ensure something like that is even less likely to happen because of the public awareness around that."
Dr Kempson said the next step will be looking at how the capsule managed to become lost in the first place.
The WA government said it would investigate the transportation of radioactive capsules on the state's roads.
The investigation will look at whether strict protocols for the preparation and transport of radioactive materials were followed.
One radioactive capsule is transported on WA's roads each week.
"How these things are transported needs to be re-looked at, I mean it does puzzle me how such a thing can fall off the back of a truck," Emergency Services Minister Stephen Dawson said.
The state government is also reviewing its penalties for mishandling radioactive materials after it was revealed the penalty for failing to safely store, pack and transport such items was only $1,000.
Editor's note (16/2/23): An earlier version of this article stated mining as a source of radioactive caesium. This has been corrected.
