Cosmic Ray Interactions in Shielding Materials

Abstract

SummaryThis document provides a detailed study of materials used to shield against the hadronic particles from cosmic ray showers at Earth's surface. This work was motivated by the need for a shield that minimizes activation of the enriched germanium during transport for the MAJORANA collaboration. The materials suitable for cosmic-ray shield design are materials such as lead and iron that will stop the primary protons, and materials like polyethylene, borated polyethylene, concrete and water that will stop the induced neutrons. The interaction of the different cosmic-ray components at ground level (protons, neutrons, muons) with their wide energy range (from kilo-electron volts to giga-electron volts) is a complex calculation. Monte Carlo calculations have proven to be a suitable tool for the simulation of nucleon transport, including hadron interactions and radioactive isotope production. The Monte Carlo simulation tool Geant4 was used for this study.This document is structured to explicitly present the data and its analysis for the six different materials considered. Each material is analyzed according to it geometry, considering ten different thicknesses of each material plus no material. The intent of this document is to provide practical guidance in the choice of shielding material for the energy range of interest (20 MeV to 10 GeV) and its particular configuration. The hydrogenous materials modeled for this study were polyethylene (PE), borated polyethylene (BPE), and water. The effectiveness of each of these materials in shielding cosmic neutrons, protons and muons was similarly poor. None of these is therefore recommended as a material to consider in shielding the detector materials in transport from cosmic rays.The result of this study is the assertion that activation at Earth's surface is a result of the neutronic and protonic components of the cosmic-ray shower. The best material to shield against these cosmic-ray components is iron, which has the best combination of primary shielding and minimal secondary neutron production.

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“…The kinetic energy losses for crossing MITO are, on average, 200 MeV, 160 MeV and more than 5 GeV for muons, protons and electrons respectively. It has to be pointed out that polyethylene has not been included in the simulation because the expected effect on the secondary particle flux is negligible in comparison with lead effect (Aguayo Navarrete et al, 2011). The result is summarized in Figure 10.…”

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