Ionising radiation is electromagnetic radiation (gamma-radiation and x-rays) or particles (alpha, beta and neutrons) with the ability to knock out electrons (ionise) from atoms or molecules hit by the radiation. In the ionisation processes radiation will transfer energy to exposed organs or organisms. The energy transfer per unit of mass is called the radiation dose, or only dose. The dose to organs or organisms is measured in the unit Sievert (abbr. Sv). In radiation protection mSv (milli Sievert = 1/1000 Sv) is frequently used.
Exposure to high radiation doses can lead to deterministic (acute) effects and damage in the exposed organ or tissue. Such effects only occur above a certain threshold value and the damage increases with increasing dose. Radiation protection involves implementation of measures to prevent high doses and acute damage in the exposed organ or tissue.
Lower radiation doses leads to an increased risk of long-term effects like cancer. In radiation protection it is assumed that the probability for developing cancer increases linearly with dose with no lower threshold value. Correspondingly it is assumed that the frequency of cancer in an exposed population depends on the sum of all individual doses. In this context, radiation protection measures include implementation of administrative and technical procedures to keep the doses to individuals and to the population as low as possible (the ALARA principle, As Low As Reasonably Achievable).
In radiation protection it is common to divide the population into two groups, occupationally exposed workers, and all other individuals in the public. In Norway, the dose limit for occupationally exposed workers is 20 mSv per year. For other individuals (the public), the dose limit is 1 mSv per year. The dose limit does not include contribution from natural background radiation or medical examinations and treatment. Doses to workers exposed to ionising radiation though their work are monitored by personal dosimeters.
The use of radiation and radioactive materials in Norway is regulated by a radiation protection act and regulations enforced by the Norwegian Radiation Protection Authority (NRPA). Several international organisations give recommendations on radiation protection and publish reviews on effects of radiation. Important organisations are the International Commission on Radiological Protection (ICRP), International Atomic Energy Agency (IAEA), United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the World Health Organisation (WHO). Recommendations from these organisations are followed by most countries.
The picture shows a personal dose meter.