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3.8 Site characterisation: Field survey and laboratory equipment used to measure radiation levels and radioactive material concentrations

Measurement is used in EURSSEM to mean:

  • The act of using a detector to determine the level or quantity of radioactivity on a surface or in a sample of material removed from a media being evaluated;
  • The quantity obtained by the act of measuring.

Three methods are available for collecting radiation data while performing a survey: direct measurements, scanning, and sampling.

Selecting instrumentation to apply one of the above three methods requires evaluation of both site and radionuclide specific parameters and conditions. Selected instruments should be stable and reliable under the environmental and physical conditions where they will be used, and their physical characteristics (size and weight) should be compatible with the intended application. The instrument and measurement method should be able to detect the type of radiation of interest, and should, in relation to the survey or analytical technique, be capable of measuring levels that are less than the derived concentration guideline level (DCGL). Numerous commercial firms offer a wide variety of instruments appropriate for the radiation measurements described in this manual. These firms can provide thorough information regarding capabilities, operating characteristics, limitations, etc., for specific equipment.

However, certain radionuclides or radionuclide mixtures may necessitate the measurement of alpha, beta, and gamma radiations. In addition to assessing each survey unit as a whole, any small areas of elevated activity should be identified and their extent and activities determined. Due to numerous detector requirements, no single instrument (detector and readout combination) is generally capable of adequately measuring all of the parameters required to satisfy the release criterion or meet all the data quality objectives of a survey.

If the field instruments and measurement methods cannot detect radiation levels below the DCGLs, laboratory methods should be used. A discussion of detection limits and detection levels for some typical instruments is presented in Section 3.3.7. There are certain radio-nuclides that will be essentially impossible to measure at the DCGLs in-situ using current state-of-the-art instrumentation and techniques because of the types, energies, and abundances of their radiations. Examples of such radio-nuclides include very low energy, pure beta emitters such as 3H and 63Ni and low-energy photon emitters such as 55Fe and 125I. Pure alpha emitters dispersed in soil or covered with some absorbing layer may not be detectable because alpha radiation will not penetrate through the media or covering to reach the detector. A common example of such a condition would be 230Th surface contamination, covered by paint, dust, oil, or moisture.