In TISOL, the 520 MeV proton beam from the main TRIUMF cyclotron strikes a production target (in our case, calcium oxide), creating the desired alkali isotopes. The target is heated to 1200°C, so the alkali atoms diffuse quickly through the material. It is also is coupled to a cylinder of refractory metal with a high work function, so alkalis are ionized upon contact with the cylinder, and then extracted as a beam of ions. The ion beam is then mass-separated (into streams of different isotopes) by a large magnet, and the particular isotope we want is selected and transported by standard "electrostatic optics" through an all-metal, ultra-high-vacuum beam line to the remote clean room where the TRINAT lasers and the experiment are housed. That enables us to shield our equipment from radiation produced by the main proton beam, as well as to separate it from the relatively poor vacuum (1x10e-9 atmospheres) near the hot target to that of the final beam line at 5x10e-13 atmospheres necessary for the trap. We stop the ion beam in another hot foil, and the atoms diffuse out and are injected into the trap region. We can trap 3000 atoms of potassium-38 or 1000 atoms of potassium-37 at a given time, enough to begin ß-decay experiments.

These isotopes have half-lives of about 1 second, ten times shorter than isotopes trapped at other labs; that means we do not have to hold the atoms in the trap as long to ensure that they decay before leaving the trap. We have also measured the precise resonant frequencies of the atoms. We do this by shining a weak probe beam in from the side and scanning the beam across the resonance, which displaces the equilibrium position of the atoms in the trap. The small (about 1/10e7) differences in resonant frequency between different isotopes let us deduce the change in nuclear charge radius that results from adding neutrons. This is a useful bread-and-butter nuclear physics experiment. It has been done elsewhere for stable and longer-lived radioactive potassium, and the resulting trends tell us about the interaction between neutrons and protons in the nucleus. We are gearing up to do the first ß-decay measurements in the fall of 1996. Laser technologies, partly driven by the optical communications industry and partly by atomic physics basic research, are improving rapidly. We suspect that we have not yet thought of the best experiments we could do with these trapped radioactive atoms.