Regulation 4 Prescribed Limits of Activity
Subject to the provisions of paragraph (2) and (3) below the limit of activity prescribed by this regulation shall be:
in the case of a site on which there is only a single radionuclide or on which there are several radionuclides all of which are in the same group and in the same form, the relevant group limit; and
in any other case, such that the sum of the fractions produced by dividing the activity of each radionuclide by its relevant group limit does not exceed one.
Where the identity of a radionuclide is not known it shall be deemed to be included in group 1.
For the purposes of the calculation to be made in accordance with paragraph (1)(b) of this regulation, where the respective activities of any of the radionuclides present are not known all such radionuclides shall be deemed to belong to the most restrictive group among them.