New radionuclide measurement systems improving search and detection capabilities for OSI deployment
The CTBTO verification system comprises an On-Site Inspection (OSI) to verify the suspicion of a forbidden nuclear test. An OSI comprises different methods of verification, one of them being the radiological survey of the inspection area. Specific equipment with high sensitivity is needed for the gamma radiation survey. Airborne and carborne survey should clearly be carried out by gross gamma counting with devices of high efficiency, whereas the definition of a sampling spot with handheld measuring devices should focus on the relevant isotopes. In fact the treaty only allows measuring some specific nuclides, which limits the inspector's ability to analyze the results and to verify the correct functioning of his measuring equipment. For example, variations in natural background may be misinterpreted easily. Until now most of the equipment used in exercises for OSI was not "blinded". The presentation will address some issues specific to this type of instrument. In recent years high resolution gamma systems with electric cooling have become really portable and reliable. Now these systems are also suitable for search tasks in the field. We carried out measurements comparing the performance of low resolution gamma measuring devices (e.g. identifinder) and high resolution gamma devices (e.g. microDetective) for searching and identifying radioactive isotopes. In an OSI the next step after finding an anomaly in the radioactive survey is to take samples and analyze these samples in the field laboratory which is located close to the base of operations. Sample preparation and sample measurement turned out to be a bottleneck in OSI performance in the last OSI exercises. Therefore, it would be of great value to the OSI if sampling could be focused to relevant spots only thus avoiding unnecessary sample analysis of non-relevant samples. Portable high resolution gamma measuring equipment may help in that.