Monte Carlo simulations of 5/8'' NaI gamma camera detector response in radiological emergency preparedness.

Following a radiological or nuclear (RN) event there is a need for measurement equipment readily available for estimation of internal contamination. Previous studies have shown that the gamma camera is a feasible tool for estimation of whole-body activity for relevant radionuclides during the recovery phase of an accident, e.g. by using whole-spectrum analysis. However, this technique is limited by the difficulties to interpret the spectral information in cases where more than one radionuclide is present in the subject. In this study, a Monte Carlo (MC) model of a gamma camera with a crystal thickness of 5/8'' was constructed using the Geant4 based MC software GATE to better understand the spectral information from multiple contaminants and to facilitate calibration for various radionuclides and contamination scenarios with several radionuclides present. The validation of the model showed good agreement with measurement data, within 15% deviation, which is an uncertainty generally accepted for RN event scenarios. The model was used to simulate the gamma camera detector response for relevant contamination scenarios in the short and the long term perspective following a nuclear power plant accident.