Number 185 (Story #1), June 28, 1994 by Phillip F. Schewe and Ben Stein|
BARE URANIUM IONS HAVE BEEN TRAPPED using an electron beam. Uranium atoms stripped of all or most of their 92 electrons have been produced before, in accelerator beams moving at nearly the speed of light. To produce stationary ions, a Livermore team uses a 198- keV electron beam to attract a sample of uranium ions stripped of 2 or 3 electrons each. The beam ionizes the uranium atoms further, producing bare (0-electron) and hydrogenlike (1- electron) uranium ions. A set of electrodes confines the ions along a 2-cm segment of the 70-micron-diameter electron beam. Measurements of these stationary ions can stringently test predictions of special relativity and quantum electrodynamics, because uranium's heavy nucleus makes relativistic and QED effects very pronounced, and the absence of all or most of the electrons prevents these effects from being muddled by electron-electron interactions. (R.E. Marrs et al, Phys. Rev. Lett, 27 June 1994).