Experimental validation of the calculated performances of the EURITRACK Tagged Neutron Inspection System

The possibility of terrorist use of explosive devices has become in recent years one of the most important issues on the international political agenda. The contrast of illicit trafficking of explosive materials by means of large commercial payloads is one of the main aspects of the problem. Currently used X-ray or gamma-ray based systems provide only density measurements of the inspected item. Neutron interrogation, on the contrary, allows the elemental density of the materials to be measured. During the last years, the Tagged Neutron Inspection System (TNIS) has been developed, which uses fan beams of 14 MeV neutrons, produced by the D+T reaction and tagged by detecting the alpha particle produced in the reaction. The TNIS improves the signal to noise ratio by electronically selecting the gamma-rays from the voxel defined by the tagging detector and by the neutron time of flight. A container interrogation device based on the TNIS is being developed within the EURITRACK (EURopean Illicit TRAfficking Countermeasures Kit) project, within the 6th Framework Program of the European Union. This system consists of a transportable deuterium-tritium neutron generator, including a position sensitive YAP alpha detector, fast neutron and gamma-ray detectors, front-end electronics and an integrated software to manage data acquisition and processing. Nuclear instrumentation has been integrated at the Ruder Boskovic Institute (IRB) of Zagreb, Croatia, and performance tests have been performed with different container fillings and targets. The design and previsional performances of this measurement system were previously determined using the Monte Carlo MCNP program. A detailed simulation of a previous IRB experimental set-up was also performed. The integration tests have provided experimental data usable to validate the calculations. Comparison of the Monte Carlo predictions with experimental data collected with the actual IRB set-up will be presented.