As you may have heard, a radioactive source has gone missing in Western Australia. Firstly, we can assure you that RSWA was not involved in any part of this event.
Also, we won’t speculate as to how this event has happened. We are in the business of sharing information and facts, and allaying fear where it is appropriate to do so.
There are thousands of these sources around WA, and they’re used and transported without any issues on a daily basis. In this case, there seems to be a failure of the control measures typically implemented.
Radioactive sources are typically highly protected within a source housing. This protects us from the radiation emitted and protects the source from damage. Sources are used commonly for density or level detection in processing plants in the mining and oil & gas sectors. These sources (and housings) are designed to be installed and left in place for 15 years without any attention (apart from regular auditing).
The housings are certified to be safe when subject to corrosion & vibration and can withstand a fall from 9m, or subject to 800 deg C for 30 minutes, with minimal impact. Transporting radiation sources is also subject to strict controls relating to the training of personnel, packaging requirements and controls for safe handling and emergency response.
We’ll be watching on with interest as this event unfolds and will share any learnings with our followers in due course.
If you’re after slightly more technical information, please read on, or refer to the attached Cs-137 MSDS.
Caesium-137 (Cs-137) (sometimes spelt Cesium) emits both beta and gamma radiation and has a half-life of 30 years. This means that after 30 years, the source will be half of it’s original activity (in this case, the original activity was 18.5 GBq). After 60 years, it will be a quarter of it’s original activity.
This Cs-137 source is in a ceramic form and is double encapsulated in stainless steel. This is to prevent the Cs-137 from becoming a contamination risk. Cs-137 used to be predominantly in a caesium-chloride salt form, which would have had different characteristics.
The source encapsulation would be to an ISO certified standard – and is known as “Special Form” under Transport Regulations. This means that the main risk from these sources is from external radiation only.
It’s likely this source has decayed from its original 18.5 GBq, but if it was at it’s full activity, we can calculate some hypothetical dose rates from an ‘unshielded’ source using what is known as a gamma factor or specific gamma ray constant. For Cs-137, this is 0.090 mSv/h per GBq at 1m.
Therefore, the dose rates from this source will be approximately 1.665 mSv/h at 1 m given the media is telling us it’s unshielded…
For perspective, spending 1 hr at 1m from this source is very close to :
- A normal amount of background radiation in Australia in a year – which is around 1.5 mSv.
- Around 17 normal chest x-rays (at around 0.1 mSv per exposure).
- The same risk of dying in a car or workplace accident in any given year.Each are around 1 in 10,000 risk – 2 mSv of radiation exposure also increases your risk of contracting a fatal cancer by around 1 in 10,000.
The risk with radiation sources dramatically increases within 1 m – we can calculate the dose rate using the ‘inverse square law’:
- At 1 cm, the dose rate will be 10,000 time higher …. 16,650 mSv/h (or 16.65 Sv/h)
- At 1mm (ie, if you were to pick the source up with your fingers), the dose rate would be 1,665 Sv/h – this will cause some serious damage to your fingers and surrounding tissues.
If you would like any further scientific information other that what has been mentioned above, please contact us on 08 6117 4095