Preventing health effects of radiation
The health effects of radiation can be divided into direct health effects and stochastic late effects. Direct effects are obvious side effects, such as tissue damage due to extensive cell damage. Stochastic effects are statistical side effects caused by a genetic modification in a single cell. Timely protective measures can significantly reduce the health effects of radiation.
In a radiation hazard situation, radiation may expose people externally, for example, when a plume containing radioactive substances passes the area, or due to radioactive substances that have landed on the ground and surfaces or an unprotected radiation source. Radioactive substances can also enter into the body (internal exposure), for example, through inhalation during the passage of a plume containing radioactive substances, from radioactive substances in food, or by absorption through the skin.
Direct or deterministic effects
The effects of ionizing radiation are deterministic when the exposure is sudden and high. Deterministic effects include radiation sickness and radiation injury.
Radiation sickness is a life-threatening condition that results from a large, sudden exposure of the whole body. The bone marrow is destroyed and there is a lack of all blood cells. In addition, the mucous membrane of the intestines is damaged and ulcers develop in the intestine. Radiation sickness is very rare, and such a case has never occurred in Finland.
Burns are another major hazard related to radiation. If a strong radiation source comes into direct contact with the skin, even brief contact is sufficient to cause a burn. However, the injury does not manifest itself immediately and the exposure cannot even be sensed, unlike when touching a hot object. It is only after several hours that the affected area becomes red, and it takes a couple of weeks for the actual blister to develop.
In the event of a severe accident at a nuclear power plant, in which radioactive substances have been widely dispersed in the environment, only an unprotected person at the site of the accident and in its vicinity may receive a radiation dose so extensive that it would have immediate effects on their health. Symptoms would occur within up to a 20-kilometre radius of the facility.
As a result of the use of a nuclear weapon, unprotected people can get radiation sickness up to a few hundred kilometres from the nuclear explosion site.
In radiation protection, it is important to ensure that no one is exposed to strong radiation sources or otherwise to doses so high that direct effects would be possible. However, potential radiation doses are usually well below the thresholds for direct effects. Then, the objective of the protection measures is to keep the cancer risk as low as possible. The risk of genetic damage is also taken into account.
Deterministic effect
Unavoidable, inevitable, direct effect, early effect. The effects of ionizing radiation are deterministic when the exposure is sudden and high. Deterministic effects include radiation sickness and radiation injury. Cf. stochastic effect.
Random or stochastic effects
Most cancers can be caused by radiation. This has been determined by observing large groups of people exposed to radiation for several decades. If, on the other hand, one person who has been exposed to radiation develops cancer at some point in their life, it is not possible to know whether this particular tumour is caused by radiation. Cancer is a very common disease, and cancer caused by radiation cannot be distinguished from cancer that has developed in any other way.
Even if a person has been exposed to a fairly large dose, cancer that occurs in older age is unlikely to be caused by radiation. Radiation causes only a small statistical increase in overall cancer morbidity. Cancer does not emerge until years after exposure, but the extra risk persists for the rest of your life.
Even a serious accident at a nuclear power plant in Finland or in a neighbouring region would not pose an immediate health risk in our country. In the event of such an accident, protective measures are mainly intended to reduce the late effects. Protective measures to reduce the radiation exposure of a large group of people are justified in order to reduce the risk of cancer, regardless of whether the increase would ever become statistically visible. However, an individual's risk of developing cancer is small in all situations.
As cancer is a common disease, an increase in cancer caused by low doses of radiation cannot be statistically detected. An exception to this is thyroid cancer in children, which is very rare under normal circumstances. Thyroid cancer is caused by radioactive iodine. If the air is expected to contain a large amount of radioactive iodine in a particular area of Finland, people are advised to take medicinal iodine tablets. For more information on taking iodine tablets, please visit the Iodine tablet protects the thyroid gland page.
Stochastic effect
Random, incidental, statistical effect, long-term effect. Stochastic detriment caused by ionizing radiation is a cancer caused by late effects or a hereditary defect caused by cell damage in the germ line. For example, if everyone in a population of 1,000 people receives a radiation dose of 20 millisieverts (mSv), then according to the current risk assessment, 1–2 people in this group will develop cancer caused by radiation.
Examples of radiation doses
A radiation dose indicates the health detriment caused by radiation. The unit of dose is the sievert (Sv). A dose is often expressed as thousandths of a sievert, that is, as millisieverts (mSv), or as its millionths, which are microsieverts (µSv).
| Dose | What symptoms can the dose cause? |
|---|---|
| 0,01 mSv | The dose received by a patient in dental x-ray imaging |
| 0,1 mSv | The dose received by a patient in chest x-ray imaging |
| 2 mSv | The cosmic radiation dose received by people working in aeroplanes |
| 5,9 mSv | The average annual radiation dose of a Finnish person (indoor radon, x-ray examinations, etc.) |
| 20 mSv | The maximum allowed annual dose of a radiation worker |
| 1000 mSv | A dose that, when received within less than 24 hours, causes radiation sickness symptoms (e.g. tiredness and nausea) |
| 6000 mSv | A dose that, when received within less than 24 hours, causes radiation sickness and can be fatal |
Examples of radiation dose rates
The dose rate indicates the size of the dose received by a person over a given period of time. The unit of dose rate is sieverts per hour (Sv/h).
| Dose rate | Example |
|---|---|
| 0,04–0,30 µSv/h | Natural background radiation in Finland. |
| 0,2–0,4 µSv/h | When this dose rate is exceeded, the automatic radiation meter of the radiation monitoring network in Finland sounds an alarm. In Finland, each measuring station has its own alarm limit, the level of which is determined on a station-by-station basis The alarm limits in Finland are 0.2–0.4 µSv/h. The differences are mainly due to the level of natural radioactivity in the soil around the sensor. |
| 5 µSv/h | The dose rate when flying at a height of 10 kilometres. |
| 5 µSv/h | The highest dose rate measured in Finland after the Chernobyl accident. |
| 10 µSv/h | Some protective measures will be taken. For example, staying outside unnecessarily should be avoided. |
| 30 µSv/h | Dose rate measured at a distance of one metre from a patient receiving radionuclide therapy. When the reading is below this, the patient can go home. |
| 100 µSv/h | Taking cover indoors. In addition, other protective measures are needed, such as preventing access to the danger zone. |