CIEMAT WBC capabilities for responding in case of nuclear and radiological emergencies.

Abstract

Nuclear and radiological accidents can result in internal exposures of workers (including first responders) and general population. For this reason it is necessary precise and rapid methods are developed in order to ensure capabilities for monitoring and dose assessments of internally contaminated persons. The Whole Body Counter (WBC) of the Center for Energy, Environmental and Technological Research (CIEMAT) in Madrid, Spain, has implemented techniques to determine radioiodine in the thyroid and gamma emitters throughout the body of various age groups of children and adults. In addition, the WBC laboratory has developed a new in vivo calibration and measurement method with germanium detectors in case of contamination of gamma emitting radionuclides in wounds at different depths.

Two detection systems have been calibrated accordingly: a Fastscan counter, consisting of two NaI(Tl) detectors, and a low-energy germanium (LEGe) detection system (four detectors), which is highly efficient at low gamma energies.

A family of Lucite thyroid neck phantoms for children and adults was designed and manufactured at CIEMAT for thyroid calibration purposes. A set of whole-body phantoms of the BOMAB type was fabricated with polyethylene, and filled with distilled water in an acid medium and with a known gamma emitter mixture for in vivo monitoring calibration. In addition simulators of contaminated wounds with circular pieces of Ethyl Vinyl Acetate (EVA) were provided by Institut de Radioprotection et de Sûreté Nucléaire (IRSN) from France.

Efficiency curves depending on energy are obtained in the different counting geometries, which facilitate calculating the activities of the gamma emitting radionuclides retained in the organism when monitoring real contaminated persons. In case of intake of radionuclides retained in the thyroid or in the whole body, a curve is obtained for each age specific phantom. Moreover in case of contamination in wounds a set of efficiency curves was developed depending on the contamination depth.

The detection limits (DL) of the in vivo measurement techniques for radionuclides have been calculated from the measurements of blank phantoms or persons according to ISO 28218 standard obtaining results for each method and age. Using the limits of detection for the estimation of the minimum committed effective dose, the values obtained were lower than 1 mSv.y−1, which is below the limit for the public recommended by ICRP.