Experimental tests of the theory of spin exchange collisions in ground state hydrogen, including hyperfine effects, will be performed. Measurements of hyperfine induced frequency shift cross sections will be made near .5 Kelvin in collaboration with the University of British Columbia using their supercooled hydrogen maser. The same measurements but at 10 Kelvin will be performed at Williams College using the apparatus developed during the previous grant. The results will test the theoretical treatment of low energy atomic collisions to the degree to which collisions between hydrogen atoms may limit the stability of cryogenic hydrogen maser frequency standards.
