Systematic Analysis of Light Ion Yields and Dose Equivalents from Thick Targets Bombarded by Proton, Helium, and Heavy Ions

Galactic cosmic rays (GCR) originating from outside the solar system create a unique radiation environment in space, which is difficult to replicate on Earth. Transport codes are used to simulate the space radiation environment and to evaluate dose and dose equivalent behind shielding for manned space missions. However, the accuracy of these transport codes depends on the accuracy and availability of the experimental data used to verify the physics models. Therefore, a series of experiments were performed to study thick-target light charged particle yields produced from GCR-like ion interactions with shields.This dissertation presents secondary light charged particle (Z=1 and 2) measurements performed in November 2016 and November 2017 at the National Aeronautics and Space Administration (NASA) Space Radiation Laboratory at Brookhaven National Laboratory (BNL). Double-differential thick-target yields were calculated for protons, deuterons, tritons, helium-3, and helium-4. These yields were calculated from measurements collected by organic liquid scintillators oriented at 10, 30, 45, 60, 80, and 135 degrees with respect to the beam direction. The beams consisted of 400-, 800-, and 2500-MeV [megaelectron volt] protons and 400-, 800-, and 1500-MeV/n [megaelectron volt per nucleon] He, C, Si, Fe ions incident on thick targets (20, 40, and 60 g/cm² [grams per centimeter squared] aluminum and high-density polyethylene (HDPE), and 20 and 60 g/cm² combination of aluminum and HDPE). In the analysis, pulse shape discrimination and time of flight techniques were used to produce secondary charged particle angular-energy spectra. Additionally, the spectra were compared with Monte Carlo simulations using Particle and Heavy Ion Transport code System (PHITS) and Monte Carlo N-Particle Transport code (MCNP). Also, dose equivalents were calculated from the measured double-differential thick-target light charged particle yields using the International Commission on Radiological Protection (ICRP) 60 quality factor and the NASA quality factors for solid cancers and leukemia. These experimental data will be integrated into NASA’s uncertainty analysis for optimization of future GCR shielding design.