Review Of Monte Carlo All-particle Transport Codes And Overview Of Recent Mcnpx Features

oS(FNDA2006)088 © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence

Experimental demonstration of a compact epithermal neutron source based on a high power laser

Epithermal neutrons from pulsed-spallation sources have revolutionised neutron science allowing scientists to acquire new insight into the structure and properties of matter. Here, we demonstrate that laser driven fast (∼MeV) neutrons can be efficiently moderated to epithermal energies with intrinsically short burst durations. In a proof-of-principle experiment using a 100 TW laser, a significant epithermal neutron flux of the order of 105 n/sr/pulse in the energy range of 0.5-300 eV was measured, produced by a compact moderator deployed downstream of the laser-driven fast neutron source. The moderator used in the campaign was specifically designed, by the help of MCNPX simulations, for an efficient and directional moderation of the fast neutron spectrum produced by a laser driven source

Analytical expressions for stopping-power ratios relevant for accurate dosimetry in particle therapy

In particle therapy, knowledge of the stopping-power ratios (STPRs) of the ion beam for air and water is necessary for accurate ionization chamber dosimetry. Earlier work has investigated the STPRs for pristine carbon ion beams, but here we expand the calculations to a range of ions (1 <= z <= 18) as well as spread out Bragg peaks (SOBPs) and provide a theoretical in-depth study with a special focus on the parameter regime relevant for particle therapy. The Monte Carlo transport code SHIELD-HIT is used to calculate complete particle-fluence spectra which are required for determining STPRs according to the recommendations of the International Atomic Energy Agency (IAEA). We confirm that the STPR depends primarily on the current energy of the ions rather than on their charge z or absolute position in the medium. However, STPRs for different sets of stopping-power data for water and air recommended by the International Commission on Radiation Units & Measurements (ICRU) are compared, including also the recently revised data for water, yielding deviations up to 2% in the plateau region. In comparison, the influence of the secondary particle spectra on the STPR is about two orders of magnitude smaller in the whole region up till the practical range. The gained insights enable us to propose an analytic approximation for the STPR for both pristine and SOBPs as a function of penetration depth, which parametrically depend only on the initial energy and the residual range of the ion, respectively.Comment: 21 pages, 5 figures, fixed bug with figures in v

A GPU implementation of a track-repeating algorithm for proton radiotherapy dose calculations

An essential component in proton radiotherapy is the algorithm to calculate the radiation dose to be delivered to the patient. The most common dose algorithms are fast but they are approximate analytical approaches. However their level of accuracy is not always satisfactory, especially for heterogeneous anatomic areas, like the thorax. Monte Carlo techniques provide superior accuracy, however, they often require large computation resources, which render them impractical for routine clinical use. Track-repeating algorithms, for example the Fast Dose Calculator, have shown promise for achieving the accuracy of Monte Carlo simulations for proton radiotherapy dose calculations in a fraction of the computation time. We report on the implementation of the Fast Dose Calculator for proton radiotherapy on a card equipped with graphics processor units (GPU) rather than a central processing unit architecture. This implementation reproduces the full Monte Carlo and CPU-based track-repeating dose calculations within 2%, while achieving a statistical uncertainty of 2% in less than one minute utilizing one single GPU card, which should allow real-time accurate dose calculations

Analysis of the NP-MHTGR concept: A comparison of reactor physics methods

Using the MCNP and ONEDANT analysis codes, we investigated basic neutronic characteristics of the NP-MHTGR preconceptual design. Exploratory steady-state analyses of k{sub eff}, neutron reaction rates, andtemperature reactivity coefficients were conducted to check die ability of our reactor physics methods to adequately model the highly heterogeneous NP-MHTGR reactor. Results of unit-fuel-cell analyses indicate that a three-region ONEDANT model adequately approximates the unit-fuel-cell lattice geometry. However, core-block analyses indicate that approximating an hexagonal heterogeneous block by a one-dimensional annular target cell can introduce significant calculational error. Investigating the core-block temperature coefficient of reactivity, we found that all components of the coefficient are negative and the delayed component contributes {approx}85% of the total temperature effect. Investigation of the full reactor temperature coefficient in the NP-MHTGR determined that all contributions from the active core are negative, with prompt effects again contributing {approx}15% of the total core coefficient Temperature-coefficient contributions from each of the reflector regions appear to be positive, but exhibit a smaller magnitude than those in the core. These positive contributions apparently are caused by reduced carbon and boron absorptions at the higher reflector temperatures. From a safety perspective, a conclusion as to the adequacy of the temperature coefficient cannot be drawn from its magnitude alone, but must be based on specific transient or accident analyses which incorporate all feedback effects. Calculational differences between MCNP and ONEDANT were as high as {approx} 1.2% for the reactor criticality eigenvalue and on the order of 20% for the core temperature coefficient