Doctoral Dissertations

Date of Award

5-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Nuclear Engineering

Major Professor

Lawrence H. Heilbronn

Committee Members

Yuri A. Kamyshkov, Steven E. Skutnik, Lawrence W. Townsend

Abstract

This dissertation presents double differential thick-target yields of secondary light ions (protons, deuterons, tritons, helium-3, and helium-4) produced by interactions of iron, helium, and proton ions with thick aluminum targets. Measurements were taken in March and December 2016 at Brookhaven National Laboratory’s NASA Space Radiation Laboratory. During this experiment, ion beams of 400- and 800-MeV/N [megaelectron volt per nucleon] iron, 400- and 800-MeV/N helium, and 400- and 800-MeV [megaelectron volt] protons bombarded aluminum targets of 20, 40, and 60 g/cm2 [grams per centimeter squared] thickness. An additional aluminum target of 60 g/cm2 thickness was placed 3.5 m downstream to model the observed increase in secondary particle yields in an enclosed space. Surveys of light ions were taken with organic liquid scintillators at 10° [degrees], 30°, 45°, 60°, 80°, and 135° off beam axis. Light ion event contributions were discerned from the total signals in the liquid scintillators by comparing the energy deposited in the liquid scintillator versus time of flight. Combined with a pulse shape discrimination technique, these methods allowed for the identification of Z=1 and Z=2 isotopes. Double differential thick-target yield versus energy spectra were then constructed for the light ion events using the time-of-flight technique.Protons were measured between 10° and 135° for all projectiles, and deuterons were measured between at least 10° and 45°. Observations of tritons, helium-3, and helium-4 were dependent upon the mass of the projectile and measurement angle. The resulting yield spectra were compared to MCNPX transport model calculations. Additionally, a subset of the results was compared to calculations performed with MCNP’s LAQGSM and ISABEL physics models, and the PHITS Monte Carlo code. Light ion yields were best modeled by MCNPX and PHITS for incident iron and helium projectiles, respectively, while light ion yields were well-modeled by both transport codes for proton projectiles. Overall, this experiment is a part of a multi-year project to supplement the existing measurements available for validation and verification of radiation transport codes, which are used to quantify radiation exposure and assess the risk of cancer incurred during long-term, manned space flight missions.

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