Surface Relaxation of Polarized Sodium Vapor

Relaxation rates have been measured for polarized Na atoms colliding with a variety of wall surfaces. We find that polyethylene and fluorocarbon rubber (Fluorel, Viton) have relaxation rates that correspond to 10-15 wall collisions before depolarization and that organo-silicones (silicone rubber, RTV, Dryfilm) have relaxation rates that correspond to more than 250 wall collisions. A number of other materials tested including metals and Teflon were found to cause relaxation at every wall collision. The relaxation rate for polarized Na atoms colliding with silicone surfaces has been studied as a function of time of exposure to Na vapor, wall temperature, and magnetic field strength. We find that such surfaces have relaxation rates corresponding to over 100 wall collisions before depolarization even after weeks of exposure to Na vapor. These measurements allow the determination of the amplitude and correlation time of the interaction on the surface that causes relaxation, and yield a value of 1.6 (+OR-) 0.5 x 10('-14) cm('2) for the Na-Na spin exchange cross section. Spin exchange cross sections have been calculated for hydrogen atoms with energy in the keV range incident on hydrogen or alkali atom targets. The cross sections generally decrease with increasing energy, but also show oscillations as a function of the energy. For a hydrogen atom with an energy of 5 keV incident on a Na atom target the spin exchange cross section is 1.2 x 10('-15) cm('2). A current application for these measurements and calculations is in the development of optically pumped polarized ion sources based on charge exchange.