Large-scale individual monitoring of internal contamination by gamma emitting radionuclides in nuclear accident scenarios

: The results obtained in a measurement campaign concerning the internal contamination by gamma emitting radionuclides of a large number of individuals are presented in this work. The aim is to assess the goodness of a spectrometric method in an emergency response following a nuclear power plant accident or a spread of radionuclides in the atmosphere due to a terroristic act. A HPGe portable spectrometer, deployed in a collective protection apparatus, was used for both whole-body and thyroid measurements. An adult Bottle Mannikin Absorption (BOMAB) and thyroid phantoms were used to evaluate the detector performance. The BOMAB phantom was provided by the Italian Institute of Ionizing Radiation Metrology (INMRI) for the ENEA intercomparison exercise. Thyroid phantoms were provided by the Belgian Nuclear Research Centre for the "Child and Adult Thyroid Monitoring After Reactor Accident" European intercomparison exercise. The instrument performance was further evaluated by collecting spectral data from healthy volunteers, using acquisition times of 180 s and 100 s, respectively, for whole-body and thyroid measurements. The detector showed a good accuracy in quantifying radionuclide activities in the adult BOMAB and in the thyroids of persons of all ages. The proposed method allows to detect in vivo activities leading to a committed effective dose E(50) and committed thyroid equivalent doses HT greater than 2 mSv due to all gamma emitting fission products, if the scan is performed within five days after intake. Assuming, for instance, an acute inhalation of Cs-137 and I-131, the obtained detection limit values for adult lead to a E(50) value equal to 0.08 mSv and a HT value of 0.27 mSv. The E(50) and HT values showed that the proposed method can be successfully used when the dose assessment must be rapidly performed for a large number of individuals in the eventuality of the scenarios previously mentioned.