Spin-exchange and spin-destruction rates for the 3He-Na system -: art. no. 062705

Optically pumped Na is used as a spin-exchange partner to polarize He-3. Polarizations around 20% have routinely been achieved in sealed spherical glass cells containing He-3, N-2, and a few droplets of Na. An optical technique has been developed to determine the Na-He-3 spin-exchange rate coefficient. By monitoring the Na spin relaxation "in the dark," the average Na-Na spin-destruction cross section at 330 degreesC is estimated to be around 5x10(-19) cm(2). This value is 2-5 (15-30) times smaller than the previously reported values for the K-K (Rb-Rb) spin-relaxation cross section. In the temperature range 310-355 degreesC the spin-exchange rate coefficient is found to be (6.1+/-0.6)x10(-20) cm(3)/s with no detectable temperature dependence. This value is in good agreement with a previous theoretical estimate reported by Walker and it is only slightly lower than the corresponding Rb-He-3 spin-exchange rate coefficient. The total Na-He-3 spin-destruction rate coefficient is, within errors, found to be the same as the Na-He-3 spin-exchange rate coefficient, thereby indicating that the maximum possible photon efficiency may approach unity for the Na-He-3 system. A technique, in which a charge-coupled device camera is used to take images of faint unquenched fluorescence light, has been utilized to allow for an instantaneous determination of the sodium number densities during the rate coefficient measurements.