Speaker
Description
Geant4 is a vital tool for understanding and calibrating the response of space-borne radiation sensors at The Aerospace Corporation, and for understanding the space radiation environment that they measure. In the year and a half since the last Geant4 Space Users Workshop, the greatest fraction of our effort addressing sensor response has gone into the implementation and benchmarking of the adjoint Monte Carlo capability of Geant4, and of an improved sector shielding calculation using Geant4 for ray-tracing. Both are much faster than the standard forward Monte Carlo technique, but at the cost of less realistic physics; their particular advantage is that they allow much faster buildup of statistics for simulations of a small sensitive target surrounded by a large amount of inert shielding, say an electronic part inside a spacecraft. We will discuss our conclusions that the Geant4 implementation of the adjoint technique is a good substitute for the forward technique in the case of externally incident electrons, but not for protons, and we will describe the improvements we made to the standard sector-shielding calculation to make it more accurate for protons.
With regard to the environments measured by our sensors, we have used Geant4 to conduct an extensive parametric study of the effects of hydrogen in the upper layers of the lunar surface on “albedo” protons and neutrons coming up to be measured by sensors in lunar orbit after their production in cosmic-ray interactions with the regolith. New since our last report at the 2017 Space Users Workshop is a study of the depths to which albedo protons and neutrons probe the presence of hydrogen; we will summarize the results of the complete study as it is being prepared for publication.
Summary
Presentation will discuss major efforts using Geant4 at The Aerospace Corporation since the last Space Users Workshop. These include implementation and benchmarking of alternatives to the standard forward Monte Carlo technique for calculation of radiation dose, and extensive simulations of secondary particles ejected from cosmic-ray interactions with the lunar surface under various assumptions about the distribution of hydrogen in the upper layers.
