NRPB-W12: Non-technical summary

Non-technical summary

In an accident involving a nuclear reactor such as those at nuclear power stations, radioactive material could be released into the atmosphere. This is very unlikely to happen in the UK but it is prudent to prepare for such an accident. The radioactive material released would be mainly in the form of gases and fine particles which would be dispersed by the wind. Measures would be taken to reduce the amount of radioactive particles that come into contact with people. However, people could breathe material in from the air, eat contaminated food, or drink contaminated water or milk.

The radioactive material released is likely to consist of a mixture of different radioactive nuclides, many of which will produce gamma rays when they decay. Like x-rays, gamma rays can easily pass through body tissues. Gamma rays produced when radionuclides decay within the body can give signals to sensitive 'detectors' placed outside the body. In this way the amount of each radionuclide in the body can be measured.

NRPB has developed a system specifically to help the local health authorities measure the amount of radioactive material inside people. This system is similar to those which are used in some nuclear establishments and hospitals but can be transported close to the accident so that people can be monitored more quickly and conveniently. It consists of a chair where the person being measured is seated and two detectors whose position can be adjusted to suit people of different size. One of the detectors is for measuring material which is distributed throughout the body and one for measuring radioactive iodine in the thyroid gland. The thyroid gland is situated at the base of the neck and naturally accumulates iodine which enters the body. Radioactive isotopes of iodine are important as they may form a large part of the release of radioactive materials.

The chair and detectors are surrounded by lead which blocks most gamma rays. This is to prevent radioactive material which is not inside the person from influencing the measurement. The measurements made with this system and other measurements would be used to give estimates of dose from radioactive material inside the body. The system has been calibrated so that the number of counts registered by the detectors can be interpreted as amounts of each radioactive material inside the body. The complete system is transported to the vicinity of the accident in two trailers and may then be operated inside a building or inside one of the trailers. The measurements made with this system and other measurements would be used to give estimates of dose from radioactive material inside the body.

Last reviewed: 1 September 2009