ICRU Report No. 53 was prepared in recognition of the fact that methods for quickly assessing radionuclides in the environment have become increasingly important, particularly in connection with accidental releases from nuclear facilities. Gamma-ray spectrometry, based on the measurement of the spectral distribution of the photon fluence, is used for the determination of activity levels in the ground or in the air and of radionuclide-specific dose quantities.
It is also applied to the control of planned releases, in dose reconstruction and environmental remediation projects and to the search for radioactive sources in the environment. The ICRU Report on this subject first covers the basic principles of gamma-ray spectrometry and then treats measurements that are performed close to the source (in-situ spectrometry), emphasizing the recent results of photon transport calculations. Report 53 then addresses the sensitivity and uncertainties involved in gamma-ray spectrometry, stressing new developments for in-situ determination of attenuation due to the surface roughness of the ground. A major section of the Report treats airborne gamma-ray spectrometry, describing the types of equipment being used, methods for mapping natural radioactivity and extending this to fission product surveys. Also discussed in this section are measurement of radioactivity in air using aircraft. The Report also treats two aspects of the determination of kerma in air and equivalent doses in human tissues or organs: (1) conversion factors relating activity distributions in the environment to organ or effective dose and (2) methods involving the unfolding of measured spectra and determining the spectral distribution of the photon fluence rate in air. An appendix to the Report contains calculation schemes for the photon fluence rate in air due to environmental radiation sources. A second appendix contains results of photon transport calculations for the kerma rate in air due to radionuclide activities that are distributed exponentially in soil. Kerma rates in air due to radionuclide distributions in air are also given.