Variance reduction techniques (VRTs) have been tremendously successful when applied to Monte Carlo radiation transport codes for which the computation time constitutes an important and a problematic parameter. In fact, many Monte Carlo calculations absolutely require variance reduction methods to achieve practical computation times. The MCNPX code has a fairly rich set of variance reduction techniques; the most known are transport cutoffs, interaction forcing, Bremsstrahlung splitting and Russian roulette. Also, the use of a phase space seems to be appropriate to reduce enormously the computing time. This work deals with the use of VRTs provided by MCNPX code for the simulation of a clinical linear electron accelerator (LINAC). Differences between various sets of VRTs are investigated. Combination between VRTs and PS is also analyzed during this study. Analysis showed that the use of VRTs and PS improve the simulation efficiency by a factor greater than 700. Finally, experimental curves of depth-dose and dose profile performed in a homogeneous water phantom are compared to dose distributions computed by use of MCNPX Monte Carlo code.
An accurate calculation of neutrons penetration through the side-shield of a Pressurized Water Reactor (PWR) is important for the estimation of nuclear heating in the thermal shields and in the Reactor Pressure Vessel (RPV), also for estimate the leakage of the particles in the reactor cavity. The cross section data and the calculation method have an important role in this kind of problems. For this object the PCA-REPLICA benchmark where the neutron transports through typical PWR were performed at AEA technology Winfrith, UK (United Kingdom). This work aims to contribute validation of the method of calculation and analyse the cross sections, for Iron ( Fe 56 ) and water ( H 1 and O 16 ), presented by: ENDF/B-VII.0, JEFF-3.1 and JENDL-4 libraries, for the PCA-REPICA benchmark, using the Monte Carlo approach by the mean of MCNPX code. The benchmark analysis was made based on the calculated-to-measured (C/M) dosimetry reaction rates of In m n n In 115 ') , ( 115 , P n n S 32 ') , ( 32 and Rh m n n Rh 103 ') , ( 103monitors, at different depth in a water/iron shield reproducing the ex-core radial geometry of a PWR. The calculations of PCA-REPLICA experiment showed us that calculation method is effective for the protection study of the REP. And generally, the average C/M ratios obtained for the three detectors are reasonably good when the uncertainties of the measurements are taken into account.
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