Slow spin relaxation of Rb atoms confined in glass cells filled with denseHe-4 gas at 1.85 K

At temperatures below 2.1 K, long-lived gaseous Rb atoms in glass cells hav e been generated with a simple method: irradiating the cells, containing He -4 gas and Rb metal, with a cw laser The obtained atomic Rb density (simila r to 10(8) cm(-3)) decreases with a 1/e time constant of about 10 s at 1.85 K. We have performed optical pumping of the Rb atoms and measured the long itudinal electronic spin relaxation time at 1.85 K as well. For processes ( such as Rb-He collisions) which do not remove the atomic Rb from the vapor, this relaxation time is found to be about 60 +/- 15 s.