Thompson Rivers University
Thompson Rivers University

Units of Radiation

Radiation Safety

Appendix 2: Units of Radiation

Units of Activity

Bq (becquerel) SI unit defined as the quantity of radioactive material in which one atom is transformed per second, or one disintegration per second (1 dps).
Ci (curie) Older unit defined as the activity of radioactive material in which the nuclei of 3.7 x 1010 atoms disintegrate per second (dps) or 2.2 x 1012 disintegrations per minute (dpm).
1 becquerel (Bq) = 1 dps = 27 pCi
1 millicurie (mCi) = 2.2 x 109 dpm = 37 MBq
1 kiloBq (kBq) = 1 x 103 dps = 27 nCi
1 microCi ( Ci) = 2.2 x 106 dpm = 37 kBq
1megaBq (MBq) = 1 x 106 dps = 27 Ci
1 nanoCi (nCi) = 2.2 x 103 dpm = 37 Bq
1 gigaBq (GBq) = 1 x 109 dps = 27 mCi
1 picoCi (pCi) = 220 dpm = 37 mBq
1 teraBq (TBq) = 1 x 1012 dps = 27 Ci

Units of Radiation Exposure

The coulomb/kilogram (C/gk) is the SI unit used to measure the radiation-induced ionizations created in a unit mass.

The roentgen (R) is the old unit defined as the quantity of radiation that produces ions carrying one statcoulomb of charge per cubic centimetre of air at 0oC and 760 mm Hg. The milliroentgen (mR) is a commonly used unit for the display or readout on survey meters and portable detection units.

1R = 258 microcoulomb (C) /kg
1 mR = 0.258 C/kg
1 C/kg = 3876 R

Units of Absorbed Dose

The gray (Gy) is the SI unit used to measure the energy imparted to irradiated matter and is defined as the absorbed radiation dose of one joule (J) per kg.

The rad (Radiation Absorbed Dose) is the old, but still commonly used unit, defined as an absorbed radiation dose of 100 ergs/g or 0.01 J/kg.

1 gray (Gy) = 1J/kg = 100 rads

Units of Relative Biological Effectiveness (RBE)

The Sievert (SV) is the SI unit that takes into account the biological effects of the particular radiation emission into the absorbed dose. It is defined as the absorbed dose in grays multiplied by the appropriate quality factor (QF). The quality factor is based on the collision stopping power of the incidient particle and is a measure of the potential biological injury of a particular type of radiation. For gamma and X-rays the quality factor is 1. The Sievert replaces the rem (rad equivalent in man).

1 Sv = 1 Gy x QF
1 Sv = 100 rems
1 rem = 1 rad x QF
1 mSv = 100 mrems = 0.1 rems
1 Sv = 100 rems

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