Studies on laser isotope separation in Kyoto University

This report presents a historical summary of studies on laser isotope separation which have been conducted in Kyoto University, Japan. Separation of isotopes can be carried out by selective excitation of molecular vibration. An attempt was first made to separate adsorbed molecules by selectively exciting their vibrations using a CO2 laser, but satisfactory results were not obtained. The matrix isolation method was then used to migrate molecules selectively in an Xe solid matrix at low temperatures. The separation factor was greater than 15 for 11BCl3-10BCl3 separation. Another study showed that the position of an infrared absorption peak can be varied by changing the composition of a binary matrix, making it possible to adjust the peak position to the laser vibration. It is also found that unexcited molecules, rather than excited ones, were released from a solidified rare gas matrix when a pulse wave of CO2 laser is applied (laser sputtering). This apparently unusual phenomenon is briefly discussed in relation to the mechanism of Xe sublimation, concluding that it is attributed to the fact that the sublimation is suppressed by laser irradiation. The report also describes an effect of laser irradiation on gas permeability of polymer films and methods for selective separation by taking advantage of this effect. (Nogami, K.)