Chernobyl local describes feeling of radiation contamination
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A tiny, pea-sized, radioactive capsule has been lost somewhere in the desert of Western Australia, with experts warning that prolonged, close exposure to the container could cause serious harm. The capsule, which contains a small amount of the radioactive isotope ceasium-137, was lost around two weeks ago after it fell off a transport truck travelling from the Gudai-Darri mine in the Pilbara region and a storage depot in the city of Perth. This route — along which authorities are searching this week with radiation detectors — covers a whopping 870 miles, about the same distance by road as the journey from Land’s End to John O’Groats.
The tiny radioactive source was part of a so-called density gauge, a device used by the mining industry to measure the density and inner structure of materials.
It is believed that the vibration of transit shook the machine loose — a mounting bolt and matching screw is also missing — allowing the 6mm wide, 8mm long metal capsule to roll out of gaps in both the gauge and the truck carrying it.
Given the size of the capsule, officials fear that it could easily have been picked up in the tread of another vehicle’s tyres and transported further afield — or, worse, have broken open, increasing the potential health risks.
Rio Tinto — the firm which operates the Gudai-Darri mine — are reported to have apologised for the loss of the capsule, having told BBC News that they are conducting an investigation “to better understand what went wrong in this instance”.
Biophysicist Professor Ivan Kempson of the University of South Australia said: “Loss of radioactive material like this is exceptionally rare, but has occurred in part due to the very small size of the capsule.
“The primary concern is the potential impact on health of a person or people who could be close to the capsule.
“We are all exposed to a constant level of radiation from natural materials around us and the foods we eat. However, if someone is too close to a concentrated source of radiation — like this capsule — for too long, then it will cause problems from radiation toxicity.
“The worst-case scenario is that someone picks up the capsule, finds it curious and keeps it in a pocket, which has happened overseas before.”
In early 1999, for example, a welder in Yanango, Peru, pocketed an iridium-192 source used for radiography — and the high radiation dose he received ultimately forced doctors to amputate his leg. The man’s family was also exposed to radiation in the process.
Prof. Kempson added: “Hopefully, the media attention will avert [things like] this from happening. If the capsule is lost in an isolated area, it will be very unlikely to have much impact.
“The impact from radiation will be worse the closer you are, and the longer you are exposed to a concentrated source.
“If you were close to this capsule for a minute or two, there is little reason for concern. There will be greatly diminished risk if you are more than tens of metres away from it.”
In fact, explained medical physicist Dr Pradip Deb of the Royal Melbourne Institute of Technology, someone standing within a metre of the missing capsule for an hour would likely receive a two millisievert dose.
This is equivalent to the amount of radiation involved when receiving a CT scan of the head — but double the effective dose recommended for the public by the International Commission on Radiological Protection.
Dr Deb added: “The radiation capsule contains caesium-137. It is normally a sealed source — meaning, if it is not broken, it will not contaminate the soil or environment.
“In that case, if the capsule is never found, it will not contaminate or transfer radioactivity into the surrounding soil.
“But caesium-137 has a half-life [the time taken for half of the substance to undergo radioactive decay] of about 30 years, meaning that the capsule will be somewhat radioactive for the next 300 years.”
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As nuclear medicine specialist Professor Dale Bailey of the University of Sydney noted, however, the risk posed by the capsule is higher if the container is somehow breached.
He explained: “Such an incident could happen if, for example, a truck were to run over the capsule, which is quite small.
“There are two main hazards to humans from this material — contamination of the skin, or worse, ingestion […] if the contained is ruptured; and exposure to the gamma rays that the source is emitting (the beta particle won’t penetrate the containment vessel).”
The former is a more serious concern, he said, because without the shielding of the capsule, the source’s emission of beta particles will be able to cause serious damage.
He added: “There would be initial reddening of the skin or tissue and, in severe cases, ulceration and potentially death of the tissues.
“If swallowed, it would potentially cause bleeding in the gut and ulceration, which can lead to significant complications.”
Finding the lost source, Prof. Bailey added, will not be an easy task to accomplish. He said: “Given the large distance involved , it will be akin to finding a needle in a haystack.
“Radiation detectors on moving vehicles can be used to detect radiation above natural levels, but the relatively low amount of radiation in the source means that they would have to ’sweep’ the area relatively slowly.”
There is the potential, the scientist added, for members of the public to assist in the hunt.
He explained: “Any mobile phone can be turned into a radiation detector by installing an app and covering the camera lens.
“Anyone detecting radiation levels above the normal background should identify and seal off the potential site location with appropriate signage, maintain a large distance from the source, minimise the amount of time monitoring the radiation emitted and call the local Environment Protection Authority.”
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