An experimental test will be made of theory which includes hyperfine structure effects in low energy electron spin exchange collisions between ground state hydrogen atoms. Measurements of hyperfine-induced frequency-shift cross sections will be made at 0.5 Kelvin using a superfluid liquid helium surface atomic hydrogen maser (at the University of British Columbia) and at 10 Kelvin with a new solid neon surface hydrogen maser (at Williams College). Results will also test the degree to which collisions between hydrogen atoms may limit the stability of cryogenic hydrogen maser frequency standards.
