What is Iridium-192?
It is a man-made radioactive form (isotope) of the metallic element iridium with a half-life of 74 days. It emits radiations that are very useful for taking pictures of welds through the metal (exactly like an X-ray) to look for flaws. This is called Non Destructive Testing (NDT). It is therefore important for ensuring the safety of structures and pressure vessels. It is also used in medicine to treat some types of cancer – this is called brachytherapy.
What does the source look like?
It is a small metal pellet, secured in a shielded tube. It is very robust.
What type of radiation does it emit?
Beta particles and gamma rays, easily detected with a Geiger counter.
How does NDT work?
The radioactive iridium source is screwed into a portable steel/lead pot. The operator carries this to the weld, positions it, puts a photographic film or digital detector behind the weld, opens a shutter briefly and takes a picture.
What keeps the radiographer safe?
The operator sets up a controlled area and keeps behind the beam. They also make sure that no bystanders are in front. The fundamental radiation protection principles of time, distance and shielding are applied.
As it is harmful, should it be banned?
No as it is used to protect life and save lives on a daily basis. There are risks associated with it, as with any harmful substance, however these can be managed in the same way that the risk of driving a car can be managed.
Why is it not too serious if it goes missing or is stolen?
It can be very harmful if held close to the body for minutes or longer. However, if there is sufficient distance from the Iridium-192 then there is little risk of harm though it does need to be treated with respect, by competent people. Eventually it will simply decay away to nothing as all the time it is stored somewhere it is decaying away to other metals (platinum and osmium) which are not radioactive. As it has a half-life of 74 days, in ten half lives (roughly two years) it will have decayed away to 0.1 per cent of the quantity.
Why is it useful to terrorists?
It has the potential to be misused as a weapon rather than a beneficial use and this is the case with almost all radioactive sources. The concern is that it could be strapped to explosives to make a 'dirty bomb'. This would make a radioactive mess but is not likely to seriously harm many people beyond those who might be hurt by an explosion. It would need the affected area to be evacuated and controlled while it is dealt with however it is more of a spectacular event than really harmful in the long term. It provides very good picture opportunities for the terrorists – people in protective clothing and equipment.
Why do radiographers talk about 'bombing' a weld?
This is black humour jargon as the equipment cannot explode.
Are there international controls on Iridium-192?
There are international regulations on how to transport it safely. In some countries, including the UK, there are very strong arrangements to ensure its security so that terrorists would find it extremely difficult to locate. In addition, the International Atomic Energy Agency (IAEA) and the World Institute for Nuclear Security (WINS) provide advice and support to governments, regulators and users to help ensure the security of radioactive materials in countries that need it.
What is polonium-210?
Polonium is a naturally occurring radioactive element. It is formed during the radioactive decay of uranium and thorium. It was first isolated in1898 thanks to the work of the distinguished Polish scientist Marie Curie, hence the name polonium. The isotope polonium-210 comes from uranium-238 via a long series of transformations that include radium-226 (radium was once used extensively in the luminising industry) and radon gas. Polonium-210 is also radioactive and decays by emitting alpha particles. The half life of the process (the time for the amount of radioactivity to decrease by half) is about 138 days during which the polonium decays to a non radioactive isotope of lead.
How is polonium-210 made?
Polonium-210 can be extracted from uranium bearing rocks e.g. granite. It can however be made in larger quantities by bombarding the element bismuth with neutrons. The isotope bismuth-209 captures a neutron and becomes bismuth-210m. This unstable form undergoes radioactive beta decay with a half life of 5 days to become polonium-210. Some of the bismuth is also converted to thallium. Specialist research reactors, used to make radioactive isotopes for medical applications, also produce polonium-210. The amount of polonium likely to cause the symptoms seen in the Litvinenko incident can only have been produced in a large industrial scale facility.
Is polonium-210 made in nuclear power stations?
No, UK nuclear power stations are not used for this sort of work. Nor is polonium-210 a significant component of nuclear waste.
What are the uses of polonium-210?
Polonium-210 sources may be used as anti-static devices on spray guns or the polishing of plastics in industry. Anti-static guns and nozzles contain a small amount of polonium-210, encapsulated in a strip of copper and mounted in a stainless steel cartridge. The alpha radiation from the polonium-210 ionises the air within a few centimetres and allows static to discharge safely. The construction of these guns and nozzles is controlled to British Standard BS 5288:1976 (Sealed Radioactive Sources) and involves quite small amounts of polonium.
Why is polonium-210 dangerous?
The alpha particles emitted by polonium-210 can be stopped by a sheet of paper or the dead layers of the skin. For the polonium to be harmful a person would have to eat it, drink it, breathe it in or absorb it through a cut. If eaten, dependent on the chemical form of the polonium, 10-50% could be taken up by the gut. This means that 50-90% would be excreted in the faeces within a few days. After uptake to blood, polonium-210 is widely distributed though soft body tissues including bone marrow and is eventually excreted, mostly in the urine with a half time (the time taken for the level of polonium-210 to fall by half) of about 50 days.
Is any intake of polonium harmful?
Radiation doses, including those from polonium-210, are assumed to give rise to an increase in lifetime cancer risk. The larger the dose, the larger the risk. The very high radiation doses once polonium is inside the body can cause damage to tissues and organs and in the extreme can be fatal, as was seen in the victim of the LItvinenko incident.
Why does the quantity matter?
The more polonium in the body, the more cells in the lining of the gut and the bone marrow will be killed by the radiation. At very high doses so many cells will die that the ones remaining will be unable to reproduce fast enough to replace the loss. There will be infection through the gut and severe blood cell deficiency. The body will not be able to withstand these changes and death results. For smaller doses, fewer cells die and the body's natural defence mechanisms kick in. Some cells hit by an alpha particle may not be destroyed but only damaged. When these cells go on to reproduce they may replicate the damaged form. These new cells may be cancerous. This is why there may be longer term health risks from much smaller uptakes of polonium.
What about 'innocent bystanders'?l
There have been reports of small amounts of polonium-210 contamination in areas used by the public. If anyone has been internally contaminated by inadvertently ingesting or inhaling polonium-210, it is most unlikely that they would receive a radiation dose high enough to give rise to any immediate medical symptoms. The long term risk would also be small.
How can alpha radioactivity be detected?
Once inside the body, alpha radioactivity can only be detected by monitoring urine or faeces. External body surfaces, and areas such as walls, floors, carpets or airplane seats can be checked with portable (alpha) sensitive radiation monitors. The air in a room can be drawn through a filter paper and the paper monitored. Specialist laboratory tests are needed to confirm that any radioactivity found is polonium-210.
What is radon and why is it a problem?
Radon is a radioactive gas produced by radioactive decay of radium, which itself comes from the decay of uranium. The production of radon gas depends on the concentration of these radionuclides in rocks and soils. The distribution of radon is hence related to the underlying geology. Higher levels tend to be from very old rocks, usually granitic in origin. Radon gas from these rocks can be trapped in poorly ventilated buildings, thus giving the occupants a larger than normal radiation dose.
What radon reduction actions should be taken when a high level of radon gas is detected in a house?
Radon gas is present in all homes, from the minute amounts of uranium present in earth materials such as rocks, soils, brick and concrete. In most cases, the amount will be so low that no remedial action is justified. Above a certain level however, the householder may wish to apply one of several tried and tested methods to reduce radon levels in the house. The choice of method depends on the radon level and the way the house is built. For instance, increasing the ventilation, especially on the ground floor, will in most cases cause a moderate reduction in the radon level. It's a good idea to make sure that all airbricks are clear of obstructions. The most effective way to reduce high levels is to install a radon sump, a small void under a solid floor connected by a pipe to the outside. A small electric fan in the pipe continually sucks the radon from under the house and expels it harmlessly to the atmosphere. Modern sumps are often constructed from outside the house so there is no disruption inside. There is no need to rush into any of these measures. The most important thing is to find out if there really is a problem. This can be done by looking at survey results from the area or by having the radon level in the home measured. The Radiation Protection Division of Public Health England is the UK Government's adviser on Radon.
There are four main planks of the UK legislative system covering the use of radioactive materials. All of the regulations described are based on internationally agreed principles.
- The Ionising Radiations Regulations 1999 - enforced by the Health & Safety Executive (HSE) and the Ionising Radiations (Northern Ireland) Regulations 2000 enforced by the HSE for Northern Ireland. These regulations apply to all work with ionising radiation. In essence the legislation places duties on employers that work with ionising radiation to protect their employees and others such as the public and those employed by other employers. It should be noted that for some large users of radioactive materials additional controls (specified in licences) are put in place under the Nuclear Installations Act 1965, enforced by HSE.
- The Radioactive Substances Act 1993 - enforced by the Environment Agency in England and Wales and the Scottish Environmental Protection Agency (SEPA) in Scotland. The Act regulates the holding, storage and use of radioactive materials, accumulation of waste and its disposal.
- The Ionising Radiation (Medical Exposure) Regulations 2000 enforced by the Department of Health for England, the National Assembly for Wales and the Scottish Executive in Scotland. The regulations lay down basic measures for the health protection of patients against dangers of ionising radiation in relation to medical exposure.
- The Radioactive Materials (Road Transport) (Great Britain) Regulations 2002 enforced by the Radioactive Materials Transport Division of the Department for Transport. There are some inter-related regulations, for example the Carriage of Dangerous Goods and Transportable Pressurised Equipment Regulations 2004. All are concerned with the transport of radioactive materials dictating what packaging, containers and labels must be used, how they are transported and the contingency arrangements that must be in place in the event of an accident. HSE enforces some aspects of the regulatory framewor, the Civil Aviation Authority for air transport and the Marine & Coastguard Agency for sea transport. All these follow similar rules so that a single package may be transferred from one mode of transport to another without relabelling or repackaging.
Food: Does irradiation make it radioactive?
No. Radiation doses used are huge but they do not induce any residual radioactivity in the food. The purpose of food irradiation is to kill harmful organisms. This process is also used to sterilise surgical equipment.
Post: Is there an exposure hazard to people who handle mail which has been irradiated by the postal service? Can such mail contain residual radioactivity?
Irradiating mail to destroy potential biological agents does not induce any radioactivity whatsoever in the mail (paper, paper clips, binder clips). The process would be the same as that used to kill harmful organisms in food and to sterilise surgical equipment. A simple analogy is that of having an X-ray taken, when of course the patient does not become radioactive. Internet research suggests that irradiation is only being carried out in the United States on mail destined for certain Government offices. It is not thought that the practice is currently in use in the United Kingdom. The US Postal Service states 'Irradiated mail is sterile and poses no hazard. It is not and cannot be radioactive. We've found no medical or scientific link to irradiated mail and health-related complaints, such as itching and sneezing... and... the mail ... meets federal guidelines for potential carbon monoxide and ozone emissions. Irradiated mail... creates more paper dust. (31 Jan 2002) While the mail and its contents do not become radioactive, any undeveloped photographic film carried in the mail would be spoiled by the large radiation field necessary to destroy harmful organisms. Anyone planning to implement mail irradiation would have to take this into account when setting up a programme. Any views expressed in this answer are not necessarily endorsed by the Society for Radiological Protection.