R. E. Prael

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.

MCNP™ Version 5

Abstract The Monte Carlo transport workhorse, MCNP [Los Alamos National Laboratory report LA-13709-M, 2000], is undergoing a massive renovation at Los Alamos National Laboratory (LANL) in support of the Eolus Project of the Advanced Simulation and Computing (ASCI) Program. MCNP 1 Version 5 (V5) (expected to be released to RSICC in Fall 2002) will consist of a major restructuring from FORTRAN-77 (with extensions) to ANSI-standard FORTRAN-90 [American National Standard for Programming Language – Fortran-Extended, ANSI X3. 198-1992, 1992] with support for all of the features available in the present release (MCNP-4C2/4C3). To most users, the look-and-feel of MCNP will not change much except for the improvements (improved graphics, easier installation, better online documentation). For example, even with the major format change, full support for incremental patching will still be provided. In addition to the language and style updates, MCNP V5 will have various new user features. These include improved photon physics, neutral particle radiography, enhancements and additions to variance reduction methods, new source options, improved parallelism support (PVM, MPI, OpenMP), and new nuclear and atomic data libraries.

Cross-sections for nuclide production in 1-GeV proton-irradiated Pb-208

114 cross sections for nuclide production in a 1.0 GeV proton-irradiated thin 208Pb target have been measured by the direct gamma spectrometry method using a high-resolution Ge detector. The gamma spectra were processed by the GENIE-2000 code. The ITEP-developed SIGMA code was used together with the PCNUDAT nuclear decay database to identify the gamma lines and to determine the cross sections. The 27Al(p,x)22Na reaction was used to monitor the proton flux. Results of a feasibility study of the auxiliary 27Al(p,x)24Na and 27Al(p,x)7Be monitor reactions in the 0.07-2.6 GeV proton-energy range are presented as well. Most of the experimental data have been analyzed by the LAHET (with ISABEL and Bertini options), CEM95, CEM2k, INUCL, CASCADE, CASCADE/INPE, and YIELDX codes that simulate hadron-nucleus interactions.

CEM2K and LAQGSM codes as event generators for space-radiation-shielding and cosmic-ray-propagation applications

The CEM2k and LAQGSM codes have been recently developed at Los Alamos National Laboratory to simulate nuclear reactions for a number of applications. We have benchmarked our codes against most available data measured at incident particle energies from 10 MeV to 800 GeV and have compared our results with predictions of other current models used by the nuclear community. Here, we present a brief description of our codes and show some illustrative results that testify that CEM2k and LAQGSM can be used as reliable event generators for space-radiation-shielding, cosmic-ray (CR) propagation, and other astrophysical applications. Finally, we show an example of combining of our calculated cross-sections with experimental data from our LANL T-16 compilation to produce evaluated files. Such evaluated files were successfully used in the model of particle propagation in the Galaxy GALPROP to better constrain the size of the CR halo.

Present and future capabilities of MCNP

Several new capabilities have been added to MCNP4C including: (1) macrobody surfaces; (2) the superimposed mesh importance functions, so that it is no longer necessary to subdivide geometries for variance reduction; and (3) Xlib graphics and DVF Fortran 90 for PCs. There are also improvements in neutron physics, electron physics, perturbations, and parallelization. In the more distant future we are working on adaptive Monte Carlo code modernization, more parallelization, visualization, and charged particles.

Improved Intranuclear Cascade Models for the Codes CEM2k and LAQGSM

An improved version of the Cascade‐Exciton Model (CEM) of nuclear reactions implemented in the codes CEM2k and the Los Alamos version of the Quark‐Gluon String Model (LAQGSM) has been developed recently at LANL to describe reactions induced by particles and nuclei at energies up to hundreds of GeV/nucleon for a number of applications. We present several improvements to the intranuclear cascade models used in CEM2k and LAQGSM developed recently to better describe the physics of nuclear reactions. First, we incorporate the photonuclear mode from CEM2k into LAQGSM to allow it to describe photonuclear reactions, not previously modeled there. Then, we develop new approximations to describe more accurately experimental elementary energy and angular distributions of secondary particles from hadron‐hadron and photon‐hadron interactions using available data and approximations published by other authors. Finally, to consider reactions involving very highly excited nuclei (E* ⩾ 2 – 3 MeV/A), we have incorporated into CEM2k and LAQGSM the Statistical Multifragmentation Model (SMM), as a possible reaction mechanism occurring after the preequilibrium stage. A number of other refinements to our codes developed recently are also listed.An improved version of the Cascade‐Exciton Model (CEM) of nuclear reactions implemented in the codes CEM2k and the Los Alamos version of the Quark‐Gluon String Model (LAQGSM) has been developed recently at LANL to describe reactions induced by particles and nuclei at energies up to hundreds of GeV/nucleon for a number of applications. We present several improvements to the intranuclear cascade models used in CEM2k and LAQGSM developed recently to better describe the physics of nuclear reactions. First, we incorporate the photonuclear mode from CEM2k into LAQGSM to allow it to describe photonuclear reactions, not previously modeled there. Then, we develop new approximations to describe more accurately experimental elementary energy and angular distributions of secondary particles from hadron‐hadron and photon‐hadron interactions using available data and approximations published by other authors. Finally, to consider reactions involving very highly excited nuclei (E* ⩾ 2 – 3 MeV/A), we have incorporated int...

Estimation and interpretation of k{sub eff} confidence intervals in MCNP

MCNP has three different, but correlated, estimators for Calculating k{sub eff} in nuclear criticality calculations: collision, absorption, and track length estimators. The combination of these three estimators, the three-combined k{sub eff} estimator, is shown to be the best k{sub eff} estimator available in MCNP for estimating k{sub eff} confidence intervals. Theoretically, the Gauss-Markov Theorem provides a solid foundation for MCNP`s three-combined estimator. Analytically, a statistical study, where the estimates are drawn using a known covariance matrix, shows that the three-combined estimator is superior to the individual estimator with the smallest variance. The importance of MCNP`s batch statistics is demonstrated by an investigation of the effects of individual estimator variance bias on the combination of estimators, both heuristically with the analytical study and emprically with MCNP.

Estimation and Interpretation of keff Confidence Intervals in MCNP

AbstractThe Monte Carlo code MCNP has three different, but correlated, estimators for calculating keff in nuclear criticality calculations: collision, absorption, and track length estimators. The combination of these three estimators, the three-combined keff estimator, is shown to be the best keff estimator available in MCNP for estimating keff confidence intervals. Theoretically, the Gauss-Markov theorem provides a solid foundation for MCNP’s three-combined estimator. Analytically, a statistical study, where the estimates are drawn using a known covariance matrix, shows that the three-combined estimator is superior to the estimator with the smallest variance. Empirically, MCNP examples for several physical systems demonstrate the three-combined estimator’s superiority over each of the three individual estimators and its correct coverage rates. Additionally, the importance of MCNP’s statistical checks is demonstrated.

Shielding calculations for 230-MeV protons using the LAHET code system

Shielding related calculations were performed for 230-MeV protons incident upon a stopping-length iron target using the LAHET code system (LCS). Secondary neutrons and photons, produced by proton interactions with the target nuclei, were transported through a spherical concrete shield in which absorbed dose and dose equivalent tallies were produced and attenuation parameters deduced. Comparing calculated results with measurements performed with a similar target, beam, and shielding geometry, the dose equivalent production term is double the measured value. The LCS overestimates measured attenuation values at 0, 22, and 45 deg while correctly predicting the attenuation length at 90 deg. Comparison of LCS results with HETC calculations and analytical methods indicates that LCS better estimates the attenuation length and dose equivalent production.

Double-differential cross sections for the production of neutrons from Pb, W, Zr, Cu, and Al targets irradiated with 0.8-, 1.0-, and 1.6-GeV protons

Experimental results obtained by determining the double-differential cross sections for neutron production in Pb, W, Zr, Cu, and Al targets irradiated with 0.8-, 1.0-, and 1.6-GeV protons are presented. The spectra of neutrons were measured at 15°, 30°, 60°, 90°, 120°, and 150° with a time-of-flight spectrometer by using a proton beam extracted from the 10-GeV synchrotron at the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The neutrons are recorded with 5MAB-1F6BC501A/5L liquid scintillation detectors and NE110 solid-state scintillators. The experimental data in question are compared with the results of simulations based on the CEM97, LAHET, and CASCADE codes.