Resolution 9 of the 15th CGPM (1975)

SI units for ionizing radiation: gray

The 15th Conférence Générale des Poids et Mesures,

  • by reason of the pressing requirement, expressed by the International Commission on Radiation Units and Measurements (ICRU), to extend the use of the Système International d'Unités to radiological research and applications,
  • by reason of the need to make as easy as possible the use of the units for non-specialists,
  • taking into consideration also the grave risks of errors in therapeutic work,

adopts the following special name for the SI unit of ionizing radiation:

gray, symbol Gy, equal to one joule per kilogram.

Note: The gray is the SI unit of absorbed dose. In the field of ionizing radiation the gray may also be used with other physical quantities also expressed in joules per kilogram: the Comité Consultatif des Unités is made responsible for studying this matter in collaboration with the competent international organizations.

DOI : 10.59161/CGPM1975RES9E

The reader should note that the official version of this Resolution is the French text


At its 1976 meeting, the CIPM approved the report of the 5th meeting of the CCU (1976), specifying that, following the advice of the ICRU, the gray may also be used to express specific energy imparted, kerma and absorbed dose index.

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