Laser assisted isotope separation of lithium by two-step photoionization using time of flight mass-spectrometer

Abstract

Laser assisted isotope separation of lithium is carried out by isotope-selective two-step photoionization method using time of flight mass-spectrometer. The isotopes of lithium are important for nuclear industry. A narrowband tunable dye laser in combination with mass-spectrometer on tuning with 6Li (2S1/2 → 2P1/2) and 7Li (2S1/2 → 2P3/2) resonance levels confirms high degree of isotope selectivity (∼32). Both the dye laser (∼0.2 cm−1, 6 ns, 640–680 nm) and the mass-spectrometer are developed in-house and optimized. Measured relative isotopic abundance (6Li/7Li ≈ 0.080) is found in close agreement with literature. It is also found that concentration of naturally less abundant (6Li) isotope get enhanced remarkably from 7.5% up to over 72% upon precise tuning of the dye laser to 6Li (2S1/2 → 2P1/2) resonance level. Photoionization cross-sections of both the isotopes are measured as 6Li (15.53 ± 2.1 Mb) and 7Li (18.62 ± 2.4 Mb) for 2p excited state using more popular and accurate saturation technique, whereas number density are determined as N0 ≈ 5.9 × 109 and 5.62 × 1010 atoms/cm3 respectively. It is inferred that selected energy pathway [2S1/2 → ∼671 nm → 2P1/2, 3/2 → ∼337 nm → 1S0 (Li+)] gives high photoionization yield and the large (∼10 folds) isotope enrichment.