Nuclear Polarization in Gaseous 3He by Optical Pumping

Overview & Synopsis

Optical pumping can provide significant nuclear polarizations in gaseous 3He. This method, developed by Colegrove, Schearer and Walters 20 years ago, can be applied to the realization of polarized targets for nuclear physics or neutron spin state filters. Moreover, highly polarized discharges in gaseous helium can be used as sources of polarized beams of atomic or molecular ions or electrons. Some progress has been made recently to obtain higher nuclear polarizations in gaseous 3He at a higher density. Laser optical pumping can produce polarizations over 60% or more in a gas at room temperature. This can be combined with a polarization transfer technique, in which a laser is used to pump 3He in a cell at room temperature, while another cell at a few degrees Kelvin is polarized by diffusion of the atoms through a long connecting tube. Cryogenic coatings, made of solid hydrogen frozen on the coldest parts of the inside wall of the container, reduce very effectively the fast nuclear relaxation which would occur on bare pyrex walls at low temperatures. Nuclear polarizations of the order of 50% have been obtained in a relatively dense gas (n ~ 10^18 cm-3) at T