Identification of Nuclear Material with Different Gamma Spectroscopic Devices

In the context of nuclear terrorism it is essential to be able to perform fast measurements in the field at the place where a suspicious object was found. Especially in the case of a suspicion that nuclear material is involved, it is necessary to identify small amounts of plutonium or uranium and to gain information concerning the enrichment. Therefore, measurements at different uranium and plutonium samples were carried out. Uranium and Plutonium samples with different enrichments have been used for the present work. Handheld and novel devices on the basis of different detector material were used. The nuclide identification results of implemented automatic identification routines were compared to the results of manual inspection of the gamma ray spectra. The results obtained with a segmented germanium detector were taken as a reference. This detector contains two separate HPGe crystals. One is a planar germanium crystal with high resolution suitable to detect the energy lines of the uranium and plutonium gamma rays in the 100 keV range. The spectra were evaluated with the MGA/MGAU code to determine the plutonium or uranium isotope vector. The ORTEC Detective EX was used as handheld device with germanium detector. As handheld device and gamma-ray spectrometer with the most common detector material sodium iodide (NaI) the identiFINDER from the company target was used for the measurements. A very compact detector system integrated in a commercial Smartphone with gamma and neutron detection is the PoliSmart from Polimaster. This device contains a caesium iodide (CsI) scintillator for the gamma spectroscopy. A fourth type of detector material is used by the INTERCEPTOR from Thermo electron corporation which is equipped with two Cadmium-Zinc-Telluride (CZT) crystals. A relatively new detector material is lanthanum bromide (LaBr), up to now no handheld devices are available. A detector setup with a 1.5” crystal was used. The paper presents all results of the enrichment analyses as well as the influence of shielding material. These results may help to interpret results obtained at radioactive material of unknown composition and therefore make a contribution to the work against nuclear terrorism.