Assessment of Variation of Nuclear Material Shape on the Performance of a Non-Intrusive Verification System using...

Non-Intrusive Systems (NIS) are used to verify sensitive Nuclear Materials (NMs). The possibility of manipulation should be taken into consideration during this activity. This may take place in different ways including NM mass, shape or the container of NM. In such activity, usually the shape of the verified NM is not known. The question to be raised in such cases is that, to what extent the variation in NM shape affects the verification results. To investigate this issue, the Monte Carlo (MC) method is used to estimate this effect. Uranium samples having six different shapes (Distributed Cylinders, Cone, Cube, Parallel Rectangles, Cylinder, Sphere) are assumed to be measured with High Purity Germanium (HPGe) detector. For all shapes the material is considered to be uranium metal with identical mass and volume; and with 80% ²³⁵U isotopic content. Nine MC input files are constructed for this evaluation. All models are employed for calculating the Absolute Full Energy Peak Efficiency (AFEPE) of the planar HPGe detector at different gamma energy lines associated to ²³⁵U and ²³⁸U isotopes (143.7, 163.2, 185.7, 205.1 and 1001.4 keV), using the Monte Carlo N-Particle Transport (MCNP) code. From the obtained results it is recommended that the measurements have to be performed at different sample-orientations and different energy lines must be considered.