Laurie S. Waters

Initial MCNP6 Release Overview

MCNP6 is simply and accurately described as the merger of MCNP5 and MCNPX capabilities, but it is much more than the sum of those two computer codes. MCNP6 is the result of five years of effort by the MCNP5 and MCNPX code development teams. These groups of people, residing in Los Alamos National Laboratory’s (LANL) X Computational Physics Division, Monte Carlo Codes Group (XCP-3), and Decision Applications Division, Radiation Transport and Applications Team (D-5), respectively, have combined their code development efforts to produce the next evolution of MCNP. While maintenance and bug fixes will continue for MCNP5 1.60 and MCNPX 2.7.0 for upcoming years, new code development capabilities only will be developed and released in MCNP6. In fact, the initial release of MCNP6 contains 16 new features not previously found in either code. These new features include the abilities to import unstructured mesh geometries from the finite element code Abaqus, to transport photons down to 1.0 eV, to transport electrons down to 10.0 eV, to model complete atomic relaxation emissions, and to generate or read mesh geometries for use with the LANL discrete ordinates code Partisn. The first release of MCNP6, MCNP6 Beta 2, is now available through the Radiation Safety Information Computational Center, and the first production release is expected in calendar year 2012. High confidence in the MCNP6 code is based on its performance with the verification and validation test suites, comparisons to its predecessor codes, the regression test suite, its code development process, and the underlying high-quality nuclear and atomic databases.

The MCNPX Monte Carlo Radiation Transport Code

MCNPX (Monte Carlo N‐Particle eXtended) is a general‐purpose Monte Carlo radiation transport code with three‐dimensional geometry and continuous‐energy transport of 34 particles and light ions. It contains flexible source and tally options, interactive graphics, and support for both sequential and multi‐processing computer platforms. MCNPX is based on MCNP4c and has been upgraded to most MCNP5 capabilities. MCNP is a highly stable code tracking neutrons, photons and electrons, and using evaluated nuclear data libraries for low‐energy interaction probabilities. MCNPX has extended this base to a comprehensive set of particles and light ions, with heavy ion transport in development. Models have been included to calculate interaction probabilities when libraries are not available. Recent additions focus on the time evolution of residual nuclei decay, allowing calculation of transmutation and delayed particle emission. MCNPX is now a code of great dynamic range, and the excellent neutronics capabilities allow new opportunities to simulate devices of interest to experimental particle physics, particularly calorimetry. This paper describes the capabilities of the current MCNPX version 2.6.C, and also discusses ongoing code development.

Monte Carlo simulations of the dosimetric impact of radiopaque fiducial markers for proton radiotherapy of the prostate

Many clinical studies have demonstrated that implanted radiopaque fiducial markers improve targeting accuracy in external-beam radiotherapy, but little is known about the dose perturbations these markers may cause in patients receiving proton radiotherapy. The objective of this study was to determine what types of implantable markers are visible in setup radiographs and, at the same time, perturb the therapeutic proton dose to the prostate by less than 10%. The radiographic visibility of the markers was assessed by visual inspection of lateral setup radiographs of a pelvic phantom using a kilovoltage x-ray imaging system. The fiducial-induced perturbations in the proton dose were estimated with Monte Carlo simulations. The influence of marker material, size, placement depth and orientation within the pelvis was examined. The radiographic tests confirmed that gold and stainless steel markers were clearly visible and that titanium markers were not. The Monte Carlo simulations revealed that titanium and stainless steel markers minimally perturbed the proton beam, but gold markers cast unacceptably large dose shadows. A 0.9 mm diameter, 3.1 mm long cylindrical stainless steel marker provides good radiographic visibility yet perturbs the proton dose distribution in the prostate by less than 8% when using a parallel opposed lateral beam arrangement.

Development and Validation of the 7Li(p, n) Nuclear Data Library and Its Application in Monitoring of Intermediate Energy Neutrons

Systematics have been created for neutron spectra from the 7Li(p, n) reaction at 0° in the 50-200 MeV proton energy region. The available experimental data in the continuum part of the spectra show satisfactory overall agreement with a representation based on the phase-space distribution corresponding to the three-body breakup process 7Li(p, n 3He)α, with empirical correction factors, which depend regularly on incident energy. Validation of the systematics included folding of the predicted neutron spectra with standard 238U neutron fission cross section. Modeled in this way distributions of neutron-induced fission events agree reasonably with experimental data.

Designing SWORD--SoftWare for Optimization of Radiation Detectors

The software for the optimization of radiation detectors (SWORD) is an integrated system (based on MCNPX [Pelowitz, DB, 2005] and GEANT4 [Agostinelli, S, et al., 2003] 3D Monte Carlo radiation transport codes) useful for the optimization of high energy radiation detection systems. A set of usable sample inputs and analysis algorithms are integrated into the system. Sample inputs include special nuclear material (SNM) targets, nuisance sources, and industrial and marine backgrounds. Analysis algorithms include spectroscopy and imaging for coded aperture detectors and Compton imagers. The system is designed from the start to be easy to use and to be deployable to detector design and system architecture study groups who are its ultimate users.

Responses to highly active antiretroviral therapy and clinical events in patients with a low CD4 cell count: late presenters vs. late starters

We investigated whether adverse responses to highly active antiretroviral therapy (HAART) associated with late HIV presentation are secondary to low CD4 cell count per se or other confounding factors.

Interacting with the SWORD package (SoftWare for the Optimization of Radiation Detectors)

We present the first version of software for the optimization of radiation detectors (SWORD): a software package designed to simplify the evaluation of different gamma-ray detector configurations or the process of conducting system architecture studies for Homeland Security and other applications. It is a fully integrated system that uses GEANT4 [2] and MCNPX [3] to conduct Monte Carlo simulations, and can analyze the resulting output in a single step. We discuss in detail the following: the SWORD 3-D graphical tool for interactively creating custom detector and environment designs; the integration of the MCNPX interface, where users can provide an MCNPX input deck and directly push it into the system; and finally the serialization of data into a binary format in order to better manage the large amount of data produced in Monte Carlo simulation.

Proton Reaction Cross Sections Measured in the BNL/AGS E943 Experiment

We have measured proton reaction cross sections over a wide mass and energy range at the Brookhaven AGS accelerator. The samples were elemental Be, C, Al, Cu, W, and Pb; the measurements were carried out at ten incident proton kinetic energies in the range 0.54 to 7.8 GeV. The experiment was similar to an earlier experiment in the 200- 550 MeV range by Renberg et al.1) The new results are in good agreement with those of Renberg et al. at the overlap point near 550 MeV. The combined results of the two experiments show an energy dependence expected from the behavior of the nucleon-nucleon cross sections. The results are reproduced by calculations based on variants of the impulse approximation and Glauber theory.

The MCNP6 Delayed-Particle Feature

The interaction of radiation with matter can cause activation or fission reactions producing unstable residuals that decay with the emission of delayed-neutron and/or delayed-gamma radiation. This delayed radiation can be exploited for a variety of purposes, including homeland security, health physics, instrumentation and equipment design, and nuclear forensics. Here we report on capability that has been developed to provide automated simulations of delayed-neutron and/or delayed-gamma radiation using MCNP6. We present new high-fidelity delayed-gamma simulation results for models based on the neutron-fission experiments conducted by Beddingfield and Cecil to illustrate and validate this powerful feature.

Delayed-Gamma Simulation Using MCNPX

Abstract Monitoring issues related to activation and fission processes occur in many health physics, instrumentation and equipment design, nuclear forensics, and homeland security applications. Gamma radiation that is emitted during these processes as a result of the radioactive decay of reaction by-products [delayed gammas (DGs)] provides unique signatures that are useful for interrogation and information acquisition. Thus, it is of compelling interest to have a simulation tool that can be used to conduct studies to provide insights into the activation and fission processes. Beginning with version 2.5.0, MCNPX has been undergoing major upgrades to facilitate DG simulations. We illustrate the upgrades for a simple multiparticle reaction model involving 60Ni and for 235U photofission caused by 12-MeV photons.