Isotope-selective laser photoionization of tin in supersonic atomic beam
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The isotope 124Sn enriched to better than 50% is needed in substantial quantity as detector material for the proposed neutrinoless double beta decay (0νββ) experiment in India (TIN.TIN). Present work investigates isotope-selective laser photoionization scheme for 124Sn. Transition to the first excited state from the ground state lies at 286.3 nm having short lifetime (~ 5 ns) and isotope shift (IS), Δν(124–120) = 441 MHz. However, the availability of high repetition rate (kHz), narrowband tunable pulsed laser in UV with low temporal jitter is a technological impediment for achieving isotopic selectivity in this transition. An alternate three-color photoionization scheme is proposed for separation of 124Sn. Laser vaporization of tin followed by supersonic expansion in a molecular beam apparatus provided the tin atomic beam. Tin atoms were first excited to the 5p6s,3P1 state from the 5p2,3P0 ground state by a broadband pulsed dye laser (λ1 = 286.3 nm). Isotopic selectivity was achieved in the second excitation step at λ2 = 855.2 nm by a narrowband continuous wave laser. Subsequently, resonant photoionization at λ3 = 694.7 nm to a newly observed autoionizing state at 60,992.9 cm−1 provided efficient photoionization. The IS for all even and hyperfine splitting for odd isotopes have been measured for the 855.2 nm transition. A selectivity factor of 24 is achieved for 124Sn isotope. The absorption cross sections of the three excitation steps is reasonably high to have an efficient photoionization scheme.
The authors are thankful to R. K. Rajawat for his encouragement and support to carry out this work. The authors are also thankful to V. S. Rawat for lending some equipment’s for conducting the experiment.
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