Sievert
Sievert
The Sievert (Sv) is the unit of measurement for the equivalent dose and effective dose of ionizing radiation in the International System of Units (SI). It is used to quantify the biological effects of radiation on living organisms, unlike the Gray (Gy), which measures only the absorbed dose, that is, the energy deposited by radiation in one kilogram of tissue (1 Gy = 1 joule/kg).
The need to introduce the Sievert arises from the fact that not all radiation has the same potential to cause biological damage: for example, for the same absorbed energy, alpha radiation is much more harmful than beta radiation or X-rays.
To account for this difference, the concept of radiation weighting factor (wR) is introduced, which expresses the different relative biological effectiveness of the various types of radiation.
The equivalent dose (HT) for a given tissue or organ T is calculated using the formula:
where:
– DT is the average absorbed dose in tissue T (in Gray),
– wR is the radiation weighting factor (for example: 1 for photons and electrons, 20 for alpha particles).
To assess the overall risk to the body, the effective dose (E) is defined, which takes into account the different sensitivity of various tissues and organs to radiation using the so-called tissue weighting factors (wT), established by the ICRP (International Commission on Radiological Protection):
Thus, the Sievert provides a measure of the health risk associated with exposure, including both the amount of radiation absorbed, its biological quality, and the sensitivity of the irradiated tissues.
Practical examples of doses in Sieverts –
– Average annual natural dose due to environmental radioactivity: approximately 2–3 mSv (millisieverts).
– Dose from a chest X-ray: 0.1 mSv.
– Dose from an abdominal CT scan: 10–15 mSv.
– Dose that can cause acute radiation sickness: ~1 Sv in a short time.
– Potentially lethal dose for 50% of exposed people without medical treatment: 3–5 Sv in a few hours.
Normative and scientific references –
ICRP Publication 103 (2007) – The 2007 Recommendations of the International Commission on Radiological Protection.
ICRU (International Commission on Radiation Units and Measurements) – definitions of radiation protection units and quantities.
IAEA – International Atomic Energy Agency: guidelines for radiation protection.
World Health Organization (WHO) – Ionizing radiation, health effects and protective measures.