Isotope separation by laser deflection of an atomic beam

Separation of isotopes of barium has been accomplished by laser deflection of a single isotopic component of an atomic beam. With a tunable narrow linewidth dye laser, small differences in absorption frequency of different barium isotopes on the 6s^{2 1}S₀₋ 6s6p¹P₁ 5536 Å resonance were exploited to deflect atoms of a single isotopic component of an atomic beam through an angle large enough to physically separate them from the atomic beam. It is shown that the principal limitation on separation efficiency, the fraction of the desired isotopic component which can be separated, is determined by the branching ratio from the excited state into metastable states. In barium, repeated absorptions and emissions on the 5536 Å transition eventually result in decay from the 6s6p¹P₁ state to the metastable 6s5d¹D₂ state. This was observed to occur for all but 3% of the¹³⁸Ba atoms. As a result, the efficiency of separation was about 0.7 for the 8 mrad atomic beam divergence employed. (Throughput was nearly 1 mg/day. No attempt was made to maximize this value.) The isotopic purity of the separated atoms was measured to be in excess of 0.9, limited only by instrumental uncertainty. The effects of near resonant atomic scattering and excitation exchange on isotopic purity are considered. Work performed under the auspices of the U.S. Energy Research & Development Administration.