Radiation-detection methods to counter radiological threats

摘要

We propose two methods as means to counter radiological terrorist acts, such as dirty-bomb or silent-source attacks. The first proposal concerns a nuclear detection system using the security cameras already installed in public spaces. We describe a method to estimate radiation dose from the amount of noise in CCD images caused by neutron radiation. Several dosimeters subjected to neutron and gamma-ray irradiation (0.1 mSv-1000 mSv) were imaged by a CCD video camera. We confirmed that the amount of noise in the CCD images varied linearly with radiation exposure. We propose a warning system to uncover shielded nuclear materials or radiation exposure devices. The second proposal is a survey system of radiological residue using long scintillation fibers. After a dirty-bomb explosion, the first responders need to search for radiological samples for subsequent nuclear forensics. We developed a position-sensitive detector with 10 m plastic scintillation fibers. The position resolution was found to be 50 cm and the dynamic range extended from 0.05 mu Sv/h to 300 mu Sv/h. We also were able to perform real-time measurements of distributed sources in situ. Stand-off detection using this device helps in surveying contaminated areas.