This standard is applicable to portable, transportable or installed assemblies intended to measure environmental air kerma rates from 30 nGy h-1 to 10 µGy h-1 (3 µtrad h-1 to 1 mrad h-1) due to X or gamma radiation of energy between at least 50 keV and 1.5 MeV( . If the assembly is to be used to measure air kerma rates in the area surrounding a nuclear reactor producing 6 MeV radiation it will be necessary to determine the response at this energy.