Number 166 (Story #1), February 25, 1994 by Phillip F. Schewe and Ben Stein METASTABLE ANTIPROTONIC HELIUM ATOMS are made by shooting beams of antiprotons into liquid helium. Experiments at the KEK lab in Japan in 1991 showed that the annihilation of some antiprotons was greatly delayed (from an expected lifetime of picoseconds to an observed interval as long as microseconds), suggesting the creation of a metastable state. The same scientists, in collaboration with physicists from Germany and Hungary, have now performed the first laser spectroscopy studies of these exotic atoms. They conclude that the longevity of the antiprotons in helium results from the formation of a neutral atom consisting of an antiproton and a helium ion. The researchers deduce that the observed emissions at a wavelength of 597 nm correspond to the transition from one high-energy, high-orbital- momentum state (n=39, l=35) to another (n=38, l=34). (N. Morita et al., 21 Feb. 1994, Physical Review Letters.)