EXPERT REACTION: Radioactive capsule lost in WA desert

The loss of such a capsule in transit is incredibly unlikely. I cannot think of any scenario where this may happen, unless foul play is involved. Effective international standards and best practices have been in place for decades, with regular internal and external audits in place.  

Assuming the capsule is intact and lost in an isolated spot in the big Australian outback, its radioactivity will slowly decrease with time; in 30 years it will be half as dangerous as today; 25% as dangerous in 60 years; and just above 10% in 90 years.

Radioactivity is a natural phenomenon. Some atoms are not stable, and spontaneously break down to other atoms, releasing large amounts of energy in the form of radiation. Some of these radioactive atoms exist in our bodies – more than 8,000 of these atoms break down every second in my own body.

The unit used to measure the health effect of radiation is called the sievert. In Australia, each of us receives around 2 milliSievert of natural radiation annually, with on average an extra 0.8 milliSievert due to medical X-rays. We do not understand well how exposure to small amounts of extra radiation affects our health, but large amounts (1,000 milliSievert) cause radiation illness and burns; 10 times as much may be lethal.

So should you be worried? If you find the capsule and do NOT pick it up, then you are pretty safe. Distance is your friend; at one meter you can stay next to the capsule for 24 hours, and get as much exposure as the average Australian gets annually from medical X-rays. At 10 meters, you can start feeling fully safe. The worst-case scenario is if the capsule is ingested. In this case, severe illness and death may occur in hours.

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 (also this and this, however, these other radiation sources were much much stronger than the capsule that is missing).

Hopefully, the media attention will avert this from happening. If the capsule is lost in an isolated area it will be very unlikely to have much impact.

Radioactive materials are very highly regulated and there are strict protocols for their handling, transport, storage and disposal. A loss of radioactive material like this is exceptionally rare but has occurred in part due to the very small size of the capsule.

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 10’s of meters away from it.

It is a very unusual situation as the radioactive capsules are transported in highly radioprotective cases according to the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA)’s strict regulation stated in the Code for the Safe Transport of Radioactive Material.

Anyhow, as the radioactive capsule is lost, relevant departments need to try their best to locate it soon, and at the same time estimate its possible impacts.

The radiation capsule contains Cs-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 Cs-137 has a half-life of about 30 years, meaning the capsule will be somewhat radioactive for the next three hundred years.

It is said that its radioactivity was 19 giga Becquerels (GBq) when it was calibrated. We can estimate its current radioactivity if the date of the last calibration is known, as the source is decaying with time by continuously emitting gamma and beta radiation.

Using a gamma radiation estimation formula, this capsule is emitting gamma photons of 662 kiloelectron volt energy which can be converted to a radiation dose of 2 milliSieverts (mSv) per hour at one metre distance from it.

If someone stands within a metre for an hour will receive 2 mSv dose, which is equivalent to an average effective dose of computed tomography (CT) scan of the head.

Dose is inversely proportional to the square of the distance. Meaning, if the distance is doubled, the dose is reduced by a factor of four. Keeping a distance from any radioactive source is the best radiation protection practice.

The loss of any radioactive material is a cause for concern. In this case, it was an industrial test source of radioactive Cesium-137. This has a moderate physical half-life (about 30 years) meaning that the source will remain radioactive and can be detected above natural background radiation levels in the environment for about 300 years. It emits beta and gamma radiation and has been used in the past for radiotherapy treatment.

Events like this are uncommon because of the stringent international standards of transport container requirements and planning approvals required for moving radioactive material around.

The radioactivity in this case will be contained within a suitable capsule and will not be a major hazard while the container is not breached. Such an incident could happen, though, 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: (a) contamination of the skin, or worse, ingestion after making physical contact with the source if the container is ruptured, and (b) exposure to the gamma rays that the source is emitting (the beta particle won’t penetrate the containment vessel).

By far the most serious concern is contamination. The beta particles, in particular, will cause serious damage to any surface that they coat. There would be initial reddening of the skin or tissue and, in severe cases, ulceration and potentially death of the tissues (“necrosis”). If swallowed it would potentially cause bleeding in the gut and ulceration which can lead to significant complications.

The exposure to the radiation being emitted by the source is of far less concern, although cannot be neglected. The main tools to minimise the damage that this can cause are time and distance: minimise the amount of time in close proximity to the source while at the same time maximising the distance between the individual and the source. One possible scenario could be that if somebody found the source they might slip it into their pocket which would be likely to cause local irradiation - not as bad as if the source were to contaminate the skin surface, but still could cause focal skin damage. If the exposure was limited to less than a few hours it is likely that any damage done would eventually repair naturally. A similar approach is currently being trialled in Australia to treat skin lesions such as Basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs).

Finding this lost source will not be easy; given the large distance involved (1400 kms) it will be akin to finding a needle in a haystack. Radiation detectors on moving vehicles can be used to detect radiation above the natural levels but the relatively low amount of radiation in the source means that they would have to “sweep” the area relatively slowly. Certainly not at 100 km/h!

Today, any mobile phone can be turned into a radiation detector by installing an app and covering the camera lens, hence enabling any potential citizen scientists to help in the search for this lost radioactive material. 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 and minimise the amount of time monitoring the radiation emitted and call the local EPA.

Caesium 137 appears to be the substance in the capsule. This is an isotope with a half-life of 30 years, radioactive for 600 years. A potassium analogue, it tends to concentrate in animal muscle and fish, and deposits in human muscle where it irradiates to nearby organs. It is a dangerous beta and high-energy gamma emitter, and is very carcinogenic.