Polarized proton target 100 cm3 . Gaseous helium 3 entered from the right and was cooled in a series of three heat exchangers before passing through an expansion valve into the target volume. The target, 10 cm long, was on the extreme left in the photograph and was filled with beads of propanediol. A waveguide fed 80 mW to the target volume at 70 GHz. The liquid helium cryostat itself sut in a helium 4 cryostat which is not shown in the photographs.