Studies and Measurements of Irradiated Solid Polarized Target Materials

Mellor, Jonathan E., Department of Physics, University of Virginia
Crabb, Don, Department of Physics, University of Virginia
Norum, Blaine, Department of Physics, University of Virginia

Experiments carried out at Thomas Jefferson National Accelerator Facility (JLab) in Newport News, Virginia, and other national labs, require the use of solid polarized targets that are used to study the internal structure of either the proton or neutron. The most common target materials used in such experiments include ammonia, butanol, pentanol, lithium hydride and their deuterated versions. A technique called Dynamic Nuclear Polarization (DNP) is used to polarize these materials at low temperatures and high magnetic fields. This method requires the introduction of paramagnetic radicals. These radicals are most commonly introduced either chemically or through irradiation. Historically, irradiations have been done at several different national laboratories with varying parameters at each laboratory. These parameters: incident electron energy, irradiation dewar geometry and cryogenic liquid, can have a significant effect on the dose deposited into the material. This thesis uses EGS4, a Monte Carlo simulation tool, to simulate and normalize irradiations done at the National Institute for Science and Technology's Medical and Industrial Radiation Facility. The results of these investigations, which are consistent with experimental polarization measurements, indicate that the above parameters have a significant effect on the dose deposited. A secondary aim of this thesis is to simulate the target beam heating for experiments carried out at the Stanford Linear Accelerator and the High Intensity Gamma-Ray Source at Duke University. Such predictions are necessary to estimate the cooling power necessary to overcome the target heating due to the presence of the beam. Lastly, the results of a series of polarization measurements are given. These measurements indicate that d-butanol, irradiated with a dose of 2-3×10 15 electrons/cm 2 , can achieve a polarization of up to +62.5%.

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MS (Master of Science)
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