What is the radioactive capsule missing in WA used for and how dangerous is it?

Authorities are continuing the search for a tiny radioactive capsule that went missing along a 1,400km stretch of Western Australian desert highway.

The 8mm by 6mm capsule fell from a secure device onto a truck traveling from a Rio Tinto mine site, north of Newman in the Pilbara region, to Perth, where it was sent for repairs.

According to WA authorities, the capsule was packed on January 10, transported from the site on January 12, and the casing it was in arrived in Perth on January 16. It was not until nine days later, on January 25, that it was discovered missing when the package was unpacked for inspection.

WA’s Department of Fire and Emergency Services said on Monday radiation specialists were searching along the Great Northern Highway by “driving north and south at slow speeds”. The department previously said it was using radiation detection equipment that could be fitted to vehicles in the search.

What is the capsule used for?

The missing capsule is a 19-GBq (gigabecquerel, a unit of radioactive decay) cesium-137 ceramic source, commonly used in radiation meters. Cesium-137 is a radioactive metal with a half-life of 30.05 years – meaning it will have half its original activity in three decades. It emits beta and gamma radiation.

In the missing capsule, the cesium is bound in a “ceramic matrix” rather than existing in loose powder form. The cesium-137 is encapsulated by steel, preventing beta particles from penetrating.

Radiation Services WA general manager Lauren Steen said capsules like this were commonly used industrially as solid radiation meters, measuring the density and flow of materials. They are widely used in the mining and oil and gas industries.

“What they’re looking at is the rate of flow or level in a pipe,” Steen said. The gamma rays emitted by the cesium-137 penetrate the pipe and are picked up by a detector at the other end.

Steen said a radioactive source like the missing capsule is typically designed to be left in place for a lifetime of about 15 years, with annual regulatory checks.

The small, round and silver capsule containing radioactive cesium-137 went missing during transit through Western Australia. Photo: Provided/PR IMAGE

According to Dale Bailey, a professor of medical imaging at the University of Sydney, the source will continue to be radioactive and detectable above natural background radiation levels in the environment for about 300 years.

In the medical setting, cesium-137 has historically been used in radiotherapy. “One of the biggest sources in a hospital is the blood irradiator — you sterilize blood with the gamma photons of cobalt-60 or cesium before you do a transfusion,” Bailey said.

How dangerous is the capsule?

Bailey said the missing capsule poses two main dangers to people: exposure, and the more serious concern, contamination, which occurs when radioactive material comes into contact with something, such as the human body or soil or a road.

“Exposure is like sitting in the sun on a hot day and getting UV radiation,” he said. “If you limit your time and maximize your distance from it, then you limit how much exposure you get.”

Authorities said spending an hour one meter away from the missing capsule was akin to receiving 10 X-rays, but Radiation Services WA estimated the radiation dose to be about 17 chest X-rays.

It estimates the capsule’s radiation dose to be about 1,665 millisieverts per hour. The normal amount of background radiation a person in Australia is exposed to in a year is about 1.5 millisieverts.

The capsule’s steel container prevents radioactive material from escaping, but if it were to break, contamination would be a bigger concern.

The beta particles — no longer contained by a barrier — can cause serious damage, leading to reddening of the skin, or ulceration or tissue death in severe cases, Bailey said.

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“When you get infected, it’s in your body,” he said. Ingestion would be very dangerous. Cesium “will go to the bone because that’s just what cesium does…then you’re going to have continuous radiation through the beta particles and the gamma rays. They are not going to be eliminated.”

“If you swallow this source, you’re likely to get local ulceration in the gut and that could lead to a hernia.”

How many similar capsules exist?

According to Radiation Services WA, there are thousands of radioactive sources in the state that are used and transported daily without problems.

“The Radiological Board of WA or any radiation health unit in any state or territory in Australia, or around the world, knows every single source – they have a database,” Steen said. “They will also have to go through a federal importation process.”

Transportation of resources between locations often requires prior submission of regulatory documents.

“Checks and balances are in place, but this is probably a bit of a wake-up call for all the companies about the serious nature of radioactivity,” Steen said.

Caesium-137 capsules are commonly imported, although Bailey said local production would be possible at the Australian Nuclear Science and Technology Organization’s (Ansto) nuclear reactor. “It’s a byproduct of the uranium fission reaction,” he said.

Steen said: “I’m not aware of anyone manufacturing it in Australia.”

The WA Radiological Board has been contacted for comment.

What happens to nuclear waste?

Once they are no longer useful, capsules like the missing source are typically exported if they were manufactured elsewhere. “Generally speaking, you can’t get rid of anything that wasn’t generated in WA within WA,” Steen said. “Anything that comes from overseas usually goes straight back.”

Bailey agreed: “Traditionally in Australia we sent it back to its source, maybe the US or Canada or Europe.”

Most of the nuclear waste that Australia does have is stored at Ansto’s facilities at Lucas Heights.

In 2020, the Morrison government selected a site near Kimba, South Australia, for a national nuclear waste facility, but the decision faced a legal challenge from Barngarla traditional owners.