Ronald P. Kensek

ITS: the integrated TIGER series of electron/photon transport codes-Version 3.0

The ITS system is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of linear time-independent coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence. Version 3.0 is a major upgrade of the system with important improvements in the physical model, variance reduction, I/O, and user friendliness. Improvements to the cross-section generator include the replacement of Born-approximation bremsstrahlung cross section with the results of numerical phase-shift calculations, the addition of coherent scattering and binding effects in incoherent scattering, an upgrade of collisional and radiative stopping powers, and a complete rewrite to Fortran 77 standards emphasizing Block-IF structure. Improvements in the Monte Carlo codes are also described.<<ETX>>

ITS Version 3.0: The Integrated TIGER Series of Coupled Electron/Photon Monte Carlo Transport Codes

ITS is a powerful and user-friendly software package permitting state-of-the-art Monte Carlo solution of lineartime-independent coupled electron/photon radiation transport problems, with or without the presence of macroscopic electric and magnetic fields of arbitrary spatial dependence. Our goal has been to simultaneously maximize operational simplicity and physical accuracy. Through a set of preprocessor directives, the user selects one of the many ITS codes. The ease with which the makefile system is applied combines with an input scheme based on order-independent descriptive keywords that makes maximum use of defaults and internal error checking to provide experimentalists and theorists alike with a method for the routine but rigorous solution of sophisticated radiation transport problems. Physical rigor is provided by employing accurate cross sections, sampling distributions, and physical models for describing the production and transport of the electron/photon cascade from 1.0 GeV down to 1.0 keV. The availability of source code permits the more sophisticated user to tailor the codes to specific applications and to extend the capabilities of the codes to more complex applications. Version 6, the latest version of ITS, contains (1) improvements to the ITS 5.0 codes, and (2) conversion to Fortran 90. The general user friendliness of the software has been enhanced through memory allocation to reduce the need for users to modify and recompile the code.

A hybrid multigroup/continuous-energy Monte Carlo method for solving the Boltzmann-Fokker-Planck equation

A hybrid multigroup/continuous-energy Monte Carlo algorithm is developed for solving the Boltzmann-Fokker-Planck equation. This algorithm differs significantly from previous charged-particle Monte Carlo algorithms. Most importantly, it can be used to perform both forward and adjoint transport calculations, using the same basic multigroup cross-section data. The new algorithm is fully described, computationally tested, and compared with a standard condensed history algorithm for coupled electron-photon transport calculations.

Dose distributions in tubing irradiated by electron beam : Monte Carlo simulation and measurement

A set of nine tube sleeves was prepared by wrapping polyethylene film around a mandrel. Wall thicknesses ranged from a nominal 0.3 to 0.6 cm and diameters ranged from 2 to 5 cm. The sleeves were irradiated with a scanning 3 MeV electron beam and were dose-mapped by indexing and unwrapping the tube sleeves and measuring the dose by an FTIR spectroscopic technique. A Monte Carlo simulation model is also described which includes all important elements of 3-D geometry necessary to describe this experiment including window foil and beam scan angle. The simulation results were compared with the highly detailed dose distribution measurements in the tubing and the differences were found to be generally within 3 to 6 percent.

Adjoint electron-photon transport Monte Carlo calculations with ITS

A general adjoint coupled electron-photon Monte Carlo code for solving the Boltzmann-Fokker-Planck equation has recently been created. It is a modified version of ITS 3.0, a coupled electron-photon Monte Carlo code that has worldwide distribution. The applicability of the new code to radiation-interaction problems of the type found in space environments is demonstrated.

ITS5 theory manual.

This document describes the modeling of the physics (and eventually features) in the Integrated TIGER Series (ITS) codes [Franke 04] which is largely pulled from various sources in the open literature (especially [Seltzer 88], [Seltzer 91], [Lorence 89], [Halbleib 92]), although those sources often describe the ETRAN Code from which the physics engine of ITS is derived, not necessarily identical. This is meant to be an evolving document, with more coverage and detail as time goes on. As such, entire sections are still incomplete. Presently, this document covers the continuous-energy ITS codes with more completeness on photon transport (though electron transport will not be completely ignored). In particular, this document does not cover the Multigroup code, MCODES (externally applied electromagnetic fields), or high-energy phenomena (photon pair-production). In this version, equations are largely left to the references though they may be pulled in over time.

Space applications of the MITS Electron-Photon Monte Carlo transport code system

The MITS multigroup/continuous-energy electron-photon Monte Carlo transport code system has matured to the point that it is capable of addressing more realistic three-dimensional adjoint applications. It is first employed to efficiently predict point doses as a function of source energy for simple three-dimensional experimental geometries exposed to planar sources of monoenergetic electrons up to 4.0 MeV due to simulated uniform isotropic fluences. Results are in very good agreement with experimental data. It is then used to efficiently simulate dose to a detector in a subsystem of a GPS satellite from the natural electron environment, employing a relatively complex model of the satellite. The capability for survivability analysis of space systems is demonstrated, and results are obtained with and without variance reduction.

LDRD project 151362 : low energy electron-photon transport.

At sufficiently high energies, the wavelengths of electrons and photons are short enough to only interact with one atom at time, leading to the popular %E2%80%9Cindependent-atom approximation%E2%80%9D. We attempted to incorporate atomic structure in the generation of cross sections (which embody the modeled physics) to improve transport at lower energies. We document our successes and failures. This was a three-year LDRD project. The core team consisted of a radiation-transport expert, a solid-state physicist, and two DFT experts.

Adaptive Three-Dimensional Monte Carlo Functional-Expansion Tallies

Abstract We describe a method that enables Monte Carlo calculations to automatically achieve a user-prescribed error of representation for numerical results. Our approach is to iteratively adapt Monte Carlo functional-expansion tallies (FETs). The adaptivity is based on assessing the cellwise 2-norm of error due to both functional-expansion truncation and statistical uncertainty. These error metrics have been detailed by others for one-dimensional distributions. We extend their previous work to three-dimensional distributions and demonstrate the use of these error metrics for adaptivity. The method examines Monte Carlo FET results, estimates truncation and uncertainty error, and suggests a minimum-required expansion order and run time to achieve the desired level of error. Iteration is required for results to converge to the desired error. Our implementation of adaptive FETs is observed to converge to reasonable levels of desired error for the representation of four distributions. In practice, some distributions and desired error levels may require prohibitively large expansion orders and/or Monte Carlo run times.

Automated Monte Carlo biasing for photon-generated electrons near surfaces.

This report describes efforts to automate the biasing of coupled electron-photon Monte Carlo particle transport calculations. The approach was based on weight-windows biasing. Weight-window settings were determined using adjoint-flux Monte Carlo calculations. A variety of algorithms were investigated for adaptivity of the Monte Carlo tallies. Tree data structures were used to investigate spatial partitioning. Functional-expansion tallies were used to investigate higher-order spatial representations.