Units of Measure – Planning Guidance for Response to a Nuclear Detonation

For the case of a nuclear detonation, persistent beta-gamma radiation levels will affect some
response decisions. For the purpose of this planning guidance, the following simplifying
assumptions about units used in measuring this radiation applies: 1 R (exposure in air) ≅ 1
rad (adsorbed dose) ≅ 1 rem (whole-body dose).2
For the purpose of this planning guidance, the rem unit is related to the Sievert unit and 1
rem = .01 Sv will be applied as the basis for comparison of traditional and SI units. Exposure
rate (R/hour [R/h]) can be expressed in terms of Sv/hour (Sv/h). Therefore: 1 R/h ≅ 0.01
Radiation Measurement Units:

Traditional Units Units SI Units
Radioactivity Curie (Ci) Becquerel (Bq)
Absorbed dose rad Gray (Gy)
Dose equivalent rem Sievert (Sv)
Exposure Roentgen (R) Coulomb/Kilogram (C/kg)
Traditional/SI Unit Conversions:
1 Curie = 3.7 x 1010 disintegrations/second 1 Becquerel = 1 disintegration/second
1 rad 0.01 Gray (Gy) or 1 centiGray (cGy)
1 rem 0.01 Sieverts (Sv)
1 Roentgen (R) 0.000258 Coulomb/kilogram (C/kg)
1 Gray (Gy) 100 rad
1 Sievert (Sv) 100 rem
1 Coulomb/kilogram (C/kg) 3,876 Roentgens

National Council on Radiation Protection and Measurements (NCRP). 2005. Key Elements
of Preparing Emergency Responders for Nuclear and Radiological Terrorism,
Commentary No. 19 (Bethesda)

2 Commentary No. 19 (Bethesda).