A gamma camera for measurements of internal contamination after a radiological accident.

After a radiological accident with the release of large amounts of radionuclides into the environment, measurements of the external and internal exposure of the public will be urgently required. The aim of this study was to investigate the properties of a gamma camera with regard to measurements of internal contamination. The gamma camera was used as a detector without any imaging function. The lowest minimum detectable activity, 100 Bq 131I in thyroid measured over the neck and 400 Bq 137Cs in the whole body measured over the trunk (1 min measuring time), was found when using the lowest (50 keV-450 keV) energy interval among the three investigated (also 550-750 keV and 450-550 keV), in measurements without a collimator. The mechanical difficulties in handling a gamma camera without a collimator may also have to be considered. It is essential to pay attention to the influence of body size on both background and sensitivity. Provided proper calibrations are carried out and routines for measurements are established, a gamma camera is useful for fast identification and quantification of internal contamination with gamma-emitting radionuclides down to levels so low that in most situations they give a low contribution to the effective dose.