Monte Carlo simulation of neutron backscattering from concrete walls in the dense plasma focus laboratory of Bologna Univ

Between 2001 and 2003 a 3.2 kJ dense plasma focus (DPF) device has been built at the Montecuccolino Laboratory of the Dept. of Energy, Nuclear and Environmental Control Engineering (DIENCA) of the Univ. of Bologna. A DPF is a pulsed device in which deuterium nuclear fusion reactions can be obtained through the pinching effects of electromagnetic fields upon a dense plasma. The empirical scale law that governs the total D-D neutron yield from a single pulse of a DPF predicts for this machine a figure of ∼107 fast neutrons per shot. The aim of the present work is to evaluate the role of backscattering of neutrons from the concrete walls surrounding the Montecuccolino DPF in total neutron yield measurements. The evaluation is performed by MCNP-5 simulations that are aimed at estimating the neutron spectra at a few points of interest in the laboratory, where neutron detectors will be placed during the experimental campaigns. Spectral information from the simulations is essential because the response of detectors is influenced by neutron energy. Comparisons are made with the simple r-2 law, which holds for a DPF in infinite vacuum. The results from the simulations will ultimately be used both in the design and optimisation of the neutron detectors and in their final calibration and placement inside the laboratory. (authors)