Semester of Graduation

August 2019

Degree

Master of Science (MS)

Department

Physics and Astronomy

Document Type

Thesis

Abstract

Synchrotron facilities require substantial amounts of shielding to protect facility staff and researchers. To meet mandatory exposure limits, the traditional combination of time, distance, and shielding of the radiation source are utilized. Because of continuous 24-7 operation of most synchrotrons, time is the least useful tool. The experimental stations for synchrotron x-ray beamlines, called hutches, enforce a minimum distance from the source, but shielding provided by hutch walls is still the principal tool for a synchrotron facility. Currently there is no single resource for synchrotron beamline hutch shielding design in the literature; most hutch shielding is designed through either over-simplified calculations or complex simulation models. The goal of this project is to produce data of scatter fraction, albedos, and tenth value layers (TVLs) for typical scattering and shielding materials that allows for an NCRP-style calculation of shielding requirements for synchrotron beamline hutches; NCRP-style calculation refers to the style of shielding calculations used in NCRP Report No. 151. In GEANT4, a typical beam geometry, scattering object, and shielding materials were modeled. A solid block of material (concrete, lead, or steel) was used to determine TVLs for primary and secondary radiation as well as albedos, while a disc of water was used to determine scatter fractions, all for primary beam energies from 10 keV to 100 keV. Because of the strong polarization of synchrotron light, x-ray scattering and albedo were substantially directed towards the ceiling and floor, rather than through the hutch’s walls, except for x-ray energies above the K-edge of lead, where fluorescence x-rays contributed substantially to albedo. Lastly, the TVLs of shielding materials for primary and secondary radiation tracked as expected with x-ray energy, with a noticeable change in magnitude when crossing a material’s K-edge.

Committee Chair

Matthews, Kenneth L II

DOI

10.31390/gradschool_theses.4935

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