Activity (becquerel, Bq) counts decays per second. Absorbed dose (gray, Gy) is energy deposited per kilogram. Equivalent dose and effective dose (sievert, Sv) weight the absorbed dose for radiation type and tissue sensitivity, so that different exposures can be compared for protection purposes. 1 Sv = 1,000 mSv = 1,000,000 μSv.
Reviewed 2026-09-24
The main quantities
| Quantity | SI unit | Meaning | Older unit |
|---|---|---|---|
| Activity | Bq | One nuclear decay per second | 1 Ci = 3.7 × 10¹⁰ Bq |
| Absorbed dose | Gy = J/kg | Energy absorbed per kilogram | 1 rad = 0.01 Gy |
| Air kerma | Gy | Kinetic energy released in air; common in X-ray measurement | — |
| Equivalent dose | Sv | Absorbed dose × radiation weighting factor w_R | 1 rem = 0.01 Sv |
| Effective dose | Sv | Sum of equivalent doses × tissue weighting factors w_T | 1 rem = 0.01 Sv |
Radiation weighting factors (ICRP 103)
| Radiation | w_R |
|---|---|
| Photons (X, γ) | 1 |
| Electrons and muons | 1 |
| Protons | 2 |
| Alpha particles and heavy ions | 20 |
| Neutrons | A continuous function of energy |
For X-rays and gamma rays w_R = 1, so 1 Gy of absorbed dose corresponds to 1 Sv of equivalent dose.
Tissue weighting factors (ICRP 103)
Red bone marrow, colon, lung, stomach, breast, remainder tissues
Gonads (heritable effects)
Bladder, oesophagus, liver, thyroid
Bone surface, skin, brain, salivary glands
Data: ICRP Publication 103 tissue weighting factors, which sum to 1.
Dose and dose rate
Survey meters usually display a dose rate such as μSv/h. Multiplying by 24 × 365 gives an annual dose only if that rate is present continuously all year; actual exposure depends on the time spent there.
References
- ICRP Publication 103 (2007): The 2007 Recommendations of the ICRP
- IAEA — Radiation, People and the Environment (2004)
- 新莱福防辐射产品手册（2024-09 V1）科普章节
This encyclopedia is for general and engineering reference and is not medical advice. Consult radiation protection or medical professionals for individual exposure assessment.