Experimental investigation of chemical reactions of laser-excited uranium atoms

The preliminary results of the experiment on chemi-ionization of uranium atoms in ground and laser-excited states are presented. Oxygen molecules were chosen as a reaction partner, since the experiment is preliminary and the handling of beams of oxygen molecules is easier than that of metal atoms. The beams of atoms and molecules were employed in crossed beam configuration to minimize the secondary reaction between reactants and produced ions. The apparatus comprises a main vacuum chamber, beam sources, a detection system, and two 10 in oil diffusion pumps and a 6 in oil diffusion pump if required. The beam of uranium atom was produced in the source consisting of a horizontally mounted tungsten crucible of hemispheric shape, 0.8 cm in diameter and 0.2 mm thick. The crucible connected to the tungsten belt was heated with current of 140 A at 7 V up to 2,400 deg. K at the central portion of the crucible. The vapor of uranium atoms from the crucible was collimated. The molecular beams were formed by the effusion from a rectangular multicapillary array made of metal foils. First, the uranium atom beam was observed through a RF quadrupole mass filter after ionization. Secondly, the uranium atom beam was intersected with the oxygen molecular beam. Ions produced by chemi-ionization were mass-analyzed and detected by the channel electron multiplier in counting mode. It seems likely that the probability of the decay from a potential curve of UO2+ is greatly enhanced as compared with that from the potential curve of U + O2. (Iwakiri, K.)