MEASUREMENTS OF THE BINDING ENERGIES OF IONS ON PLASTIC SURFACES IN LIQUID NITROGEN

To improve the present limit of the neutron electric dipole moment (nEDM) from 1.8*10-26 e. cm to ~ 3*10-28 e. cm, the nEDM@SNS experiment plans to increase neutron density by storing ultracold neutrons in superfluid helium-4. In this experiment, the central part of the apparatus consists of two deuterated tetraphenyl butadiene (dTPB) coated poly(methyl methacrylate) (PMMA) cells, which are sandwiched between grounded and high-voltage electrodes. To achieve such precision, the externally applied electric field has to be stable at the 1% level over a time period of about 1000 s. Several sources of ambient ionizing radiation generate charged particles in the cryogenic liquid. These ions and the associated electrons are adsorbed on the cell walls. Consequently, an opposing static electric field is generated, which will impact the stability of the electric field. At the University of Kentucky, we have devised a compact test setup to study the behavior of ions inside cryogenic liquids using a scaled-down version of the nEDM cell and the electrodes. In our setup, ion-electron pairs are generated by irradiating liquid nitrogen (helium) with a Cesium γ-source, and the electro-optic Kerr effect is utilized to understand the cell charging effects in the dummy measurement cell. We developed a new method to measure the binding energy of the ions or electrons bonded on insulating surfaces. Determining the binding energy can potentially reduce the data-taking time of the nEDM@SNS experiment if partial field reversal is sufficient. This dissertation presents studies of the binding energies of ions and/or electrons on dTPB-coated and uncoated PMMA surfaces in cryogenic liquid nitrogen