Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)




Todd Averett


At the Thomas Jefferson National Accelerator Facility, glass target cells containing a high density of highly polarized 3He nuclei are used in electron scattering experiments studying the substructure of the neutron. In addition to 3He, these cells contain a small amount of rubidium (Rb), potassium (K), and nitrogen (N2), which facilitate the polarization process. The work presented here represents studies of the interactions between the alkali vapor and 3He nuclei when both are polarized and unpolarized.;Our investigations into the mechanisms responsible for the relaxation of the 3He polarization have measured unusually large polarization losses. In addition, most cells studied exhibited polarization lifetimes much shorter than those typically observed in cells used for scattering experiments. These results suggest there are relaxation mechanisms that depend on whether the cell contains polarized or unpolarized alkali vapor, solid alkali, or no alkali. Previous cell studies have assumed these relaxation mechanisms are independent of the presence of alkali in any form. Modication of the polarization rate equations to include these new relaxation mechanisms are given. Further studies are needed to fully understand the origin of these additional relaxation mechanisms.;Studies of the interactions between 3He and alkali vapor, when both are unpolarized, were motivated by the need to determine the number density of 3He inside sealed cells. The system we have implemented to measure the number density examines the broadening of the absorption profiles of the D1 and D2 lines of Rb and K due to collisions with 3He and N2. However, in order to relate this broadening to the gas density, the value of the velocity-averaged collisional cross-section (broadening coefficient) for the interacting pair of atoms must be known. While the value of the coefficient has been measured for Rb, no data have been published for K interacting with 3He at the high number densities required for scattering experiments. Furthermore, pressure broadening theory predicts a temperature dependence for the coefficients, but very little experimental data has been published. In addition to broadening, a shift in the central frequency is also predicted and has been experimentally verified. We have measured both the broadening and shift of the D1 and D2 lines of Rb and K in the presence of 3He and N2 over a range of number densities and temperatures.



© The Author