Identification of nuclear material with hand-held and portable gamma and neutron measuring devices
Performing fast measurements in the field at places where suspicious objects were found is essential in the context of nuclear terrorism. Especially if nuclear material is involved, it is necessary to identify small amounts of plutonium or uranium and to gain information concerning isotopic composition. Therefore, measurements at different uranium and plutonium samples were carried out. Samples with different isotopic compositions have been used for the present work. For gamma measurements hand-held and portable devices using different detector materials were investigated. The nuclide identification results of implemented automatic identification routines were compared for the different devices and to the given source information. As hand-held device with germanium detector (Ge) the ORTEC Micro Detective with electrical cooling was used. The identiFINDER from ICx was used as an example for an hand-held device and gamma-ray spectrometer with the most common detector material sodium iodide (NaI). Another investigated detection system was the InSpector 1000 from Canberra which contains a lanthanum bromide (LaBr3) crystal. A fourth type of detector material is used by the INTERCEPTOR from Thermo which is equipped with two cadmium-zinc-telluride (CZT) crystals. Some of the measurement devices also have neutron detectors but with very small volume and therefore low efficiency. A portable neutron detector with an implemented analysis routine for the discrimination between industrial and nuclear neutron sources is the Fission Meter from ORTEC. The paper presents results obtained with the different measurement systems. The quality of the outcome of the automatic identification routines of the different detection systems varied significantly. These results depended not only on the different detector materials but also on the type of nuclear material. In general identification of uranium was considerably better than the identification of plutonium.