Searching and identifying radioactive material with hand-held high-resolution gamma detectors

In the context of the global threat of nuclear terror, detection of illicit nuclear and radioactive material is of high importance in order to prevent possible terrorist acts with dirty bombs or improvised nuclear devices (IND). Procurement of nuclear or radioactive material is generally considered to be the obstacle for terrorists which is most difficult to overcome on their way to assemble and ultimately use a dirty bomb or an IND. Therefore, sophisticated detection methods need to be employed to localize and identify illicit radioactive and nuclear material. As far as border crossings are concerned, portal monitors with large-volume detectors are best suitable for these purposes. But detection of such covert radioactive or nuclear material in places where the material is temporarily stored prior to the composition of the device or detection of the composed device requires another type of detection equipment. Mobile systems featuring high resolution gamma spectroscopy and neutron detection with a reasonably low weight to carry out thorough surveys of suspicious locations are required. Germanium detectors with liquid nitrogen cooling are commonly used in that respect. In case liquid nitrogen is not available, electrically cooled Germanium detectors are the only type of detector to fulfill the requirement of high energy resolution whereas light-weight detectors for on-site surveys are usually equipped with low-resolution crystals. The new Micro Detective device manufactured by ORTEC is supposed to be especially suitable for surveys and identification of nuclear or radioactive material at locations where it is suspected. We have performed measurements to investigate the detector's characteristics as well as measurements examining the quality of identification of the material in question. The results of identification and search tests will be shown. A comparison with other mobile search detectors will be presented including an assessment of their applicability for realistic search tasks. New easy to use high-resolution mobile search detectors may be a valuable completion to the widely used low resolution search devices and may thus help to prevent nuclear terrorism