The Heidelberg polarized alkali source E. Steffens, W. Dreves, P. Egelhof, D. Kassen, W. Weiss, P. Zupranski et D. Fick Rev. Phys. Appl. (Paris), 12 10 (1977) 1567-1570 DOI: 10.1051/rphysap:0197700120100156700
