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Ionizing Radiation: Measurement units

Measurements of ionizing radiation may characterize:

Note the special names for these units:

  • The SI unit of activity is designated the becquerel rather than the reciprocal second;
  • The SI units of absorbed dose and dose equivalent are designated the gray and the sievert, respectively, rather than the joule per kilogram.

The special names becquerel, gray, and sievert were specifically introduced because of the dangers to human health that might arise from mistakes involving the units reciprocal second and joule per kilogram, in case the latter units were incorrectly taken to identify the different quantities involved.

Measurement units
SI Brochure, from Section 2.2.2
Decisions relating to SI derived and supplementary units
SI Brochure, from Appendix 1

    SI derived units:

    12th CGPM, 1964 accepts the continued use of the curie as a non-SI unit
    13th CGPM, 1967/68 lists some examples of derived units
    15th CGPM, 1975 adopts the special names becquerel, Bq, and gray, Gy
    16th CGPM, 1979 adopts the special name sievert, Sv
    CIPM, 1984 decides to clarify the relationship between absorbed dose (SI unit gray) and dose equivalent (SI unit sievert)
    CIPM, 2002 modifies the relationship between absorbed dose and dose equivalent

    Supplementary units:

    CIPM, 1980 decides to interpret supplementary units as dimensionless derived units
    20th CGPM, 1995 decides to abrogate the class of supplementary units, and confirms the CIPM interpretation that they are dimensionless derived units
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