# Ionising Radiations Regulations (Northern Ireland) 2000, Paragraph 2

Extent: N.I.

In any case where the isotopic composition of a radioactive substance is not known or is only partially known, the quantity ratio for that substance shall be calculated by using the values specified in the appropriate column in Part I for ‘other radionuclides not listed above’ for any radionuclide that has not been identified or where the quantity of a radionuclide is uncertain, unless the employer can show that the use of some other value is appropriate in the circumstances of a particular case, when he may use that value.

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Source: https://www.legislation.gov.uk/nisr/2000/375/schedule/8/paragraph/2 (the official version)
Page: https://openlegislation.uk/ionising-radiations-regulations-northern-ireland-2000/schedule-8/paragraph-2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.