Detection of Illicit Nuclear Materials Masked with other Gamma-Ray Emitters
The purpose of this work was to experimentally determine the extent to which legal shipments of radioisotopes could be used to mask the presence of illicit nuclear materials and the means by which this can be accomplished.
A Study of Gamma Interference Situations for Nuclear Security Purposes Experiments and Simulations using the NUCLEONICA Tools
The effects of ‘overlaying’ spectra of different sources and associated interference phenomena can strongly influence nuclide identification in gamma spectrometry. These phenomena are studied both experimentally and in simulations. The results are particularly dependant on the spectral detection equipment used as well as the identification software. Various cases are developed by combining spectra of two or more isotopes. Spectra are simulated with the Gamma Spectrum Generator, a powerful web-based gamma modelling tool developed within the NUCLEONICA nuclear science portal and an MCNP-based Monte Carlo engine, the easyMonteCarlo. A comparison to experimental results, obtained with a common sodium iodide scintillator, spectrometric point sources and nuclear reference material shows that the simulation is accurate enough to investigate interference scenarios. According to different properties of the gamma spectra, various types of interferences are possible. It is found that spectra can influence each other in the photo peak region, as well as in the backscatter peak area and the Compton continuum. A further consideration of the additional effects of shielding and real-life extended source geometries shows that these do not only reduce spectrum counts but also change the spectrum shape and therefore decrease identification probability.
Microbial flora of frozen tail meat from captive Nile crocodiles (Crocodylus niloticus).
Frozen tail meat samples from nine Nile crocodiles (Crocodylus niloticus) were evaluated for microbial numbers and types. Microbial analyses yielded a mean aerobic plate count (APC, 30 degrees C) of 4.86 log cfu/g, a mean coliform count (TC, 37 degrees C) of 3.77 log cfu/g and a mean faecal coliform count (FC, 44 degrees C) of 3.40 log cfu/g. Salmonella was isolated from three samples, and beta-haemolytic streptococci from two samples. Yersinia, Aeromonas, Staphylococcus aureus and Bacillus cereus were not isolated. Typical bacterial genera recovered included Flavobacterium, Pseudomonas, Acinetobacter, Enterobacter, Moraxella, Micrococcus, Staphylococcus and Streptococcus.