doseofradiation

Dose of radiation refers to the amount of ionizing energy deposited in a material, typically human tissue, by exposure to radiation. The basic quantity is absorbed dose, measured in gray (Gy), where 1 Gy equals 1 joule of energy deposited per kilogram of matter. Absorbed dose describes the physical energy transfer and does not directly indicate potential biological effect. Historically, other quantities such as exposure, measured in air, were used; today SI units are standard.

To assess biological effect, two derived quantities are used: equivalent dose and effective dose, both measured in sievert (Sv). Equivalent dose multiplies the absorbed dose by a radiation weighting factor that accounts for the type and energy of radiation (for photons, WR ~1; for alpha particles, WR ~20). Effective dose further weights equivalent doses by tissue weighting factors, providing an overall risk estimate for radiation exposure of the whole body.

Measurement and monitoring rely on dosimeters worn by workers, including chamber-based instruments and thermoluminescent devices. In medical settings, doses vary: a chest X-ray delivers a few tens of microsieverts, while a CT scan can range from about 1 to 10 mSv. Natural background radiation is location dependent, roughly 2 to 3 mSv per year. Public exposure limits are about 1 mSv per year; occupational limits are 20 mSv per year averaged, with up to 50 mSv in a single year.

Health effects: High doses can cause deterministic effects, while low to moderate doses carry stochastic cancer risk. The linear no-threshold model is used for regulation, but actual risk at very low doses is uncertain. Protective measures include shielding, minimizing time near sources, maximizing distance, and proper dose monitoring; ALARA principle.