New approaches to molecular laser separation of uranium isotopes

Significant interest in the laser separation of uranium isotopes at the turn of the century stimulated the search for and development of a number of methods and approaches that use both atomic and molecular mechanisms of isotope separation. Effective laser methods for the separation of uranium isotopes are currently under active development in many countries. New approaches to the molecular laser isotope separation (MLIS) of uranium are reviewed. They are based on resonant isotope-selective multiphoton excitation of high vibrational states ($2\nu _3$ and $3\nu_3$) of $^{235}\rm UF_6$ and $^{238}\rm UF_6$ molecules in gas-dynamically cooled molecular flows by bichromatic IR laser radiation and the subsequent dissociation of the excited molecules by the same laser pulses. The foundations of these approaches are analyzed. The results of experiments on two- and three-photon excitation of $\rm SF_6$ molecules, whose spectroscopic properties are similar to those of $\rm UF_6$ molecules, into the $2\nu _3$ and $3\nu_3$ vibrational states by, respectively, two- and three-frequency radiation of pulsed $\rm CO_2$ lasers are presented and discussed. Specific setups and parameters of resonant two- and three-photon isotope-selective excitation of $^{235}\rm UF_6$ and $^{238}\rm UF_6$ molecules into the $2\nu _3$ and $3\nu_3$ vibrational states by bichromatic IR radiation from two pulsed $\rm CF_4$ lasers and two para-$\rm H_2$ lasers with emissions in the 16-$\mu $m region are proposed and analyzed. A method is considered for the isotope-selective excitation and dissociation of $\rm UF_6$ molecules in a mixture with a sensitizer ($\rm SF_6$ molecules) under nonequilibrium thermodynamic conditions of a shock wave. Low-energy MLIS methods for uranium based on the proposed approaches are shown to be feasible.