Adjoint Monte Carlo Simulations and Improved Sector Shielding Calculations with Geant4
AEROSPACE CORP EL SEGUNDO CA EL SEGUNDO United States
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The adjoint Monte Carlo simulation technique can be used to greatly speed calculation of radiation dose or other quantities related to a small sensitive volume, like an electronic part, inside a much larger inert shielding volume, like a spacecraft. For several years the Geant4 open-source Monte Carlo radiation transport toolkit has included the capability to perform such simulations as well as more conventional forward simulations we document here how to use this capability, qualitatively and quantitatively, and compare results of adjoint and forward Monte Carlo simulations in a simple test geometry. We find that the two methods agree well for an external radiation environment consisting of electrons, but that results from the adjoint technique are a factor of 2x to 3x too high for protons that have low enough energies to come to a stop, or nearly so, in the sensitive target. We discuss an extension of techniques already in use to combine different forward Monte Carlo simulations, in order to use a focused forward simulation to supersede results in the suspect part of the parameter space for a global adjoint simulation. We also have developed an improvement on the even faster, albeit less physically detailed, sector shielding technique to improve its accuracy as a substitute for adjoint Monte Carlo simulations of protons.
- Numerical Mathematics
- Computer Programming and Software