MLIS

MLIS (abbreviation for English molecular laser isotope separation , dt. Molecular laser isotope separation) is a process for isotope separation by lasers , in which the isotopes are present in molecular form and selectively by laser radiation of highest frequency stability and narrow band dissociates be. When using nuclear energy from uranium , the process serves to enrich the isotope ²³⁵ U , which can be fissioned by thermal neutrons .

Another type of laser enrichment is the AVLIS atomic process . Both processes have not achieved any industrial importance.

description

For uranium enrichment with the help of the molecular laser process, the gaseous compound uranium hexafluoride (UF ₆ ) is used. As with the atomic method, the isotope shift is used , i.e. the fact that the energy levels of the various isotopes also differ slightly in the term scheme of the molecular vibrations . By irradiating with laser radiation in the mid- infrared , one can achieve that certain molecular vibration levels are selectively excited and thereby only the molecules of this isotope are dissociated, i.e. H. be separated into two fragments.

The selective excitation would be relatively uncritical if the UF ₆ molecules were all in the respective ground state . However, this ground state is only about 1% occupied at room temperature due to the Boltzmann distribution . The observed absorption spectrum therefore corresponds to a mixture of transitions between different excited oscillation and rotation levels, with the lines of the different isotopes being superimposed. The width of the absorption band is therefore much larger than the isotope shift , which considerably reduces the selectivity. So you have to go to lower temperatures. At 55 K (approx. Minus 220 ° C) the occupation of the ground state reaches a value of approx. 90%.

In terms of radiation technology, there are two steps involved. The UF ₆ gas is first selectively excited with an infrared laser (for example a frequency- stabilized carbon dioxide laser ) and then dissociated into UF ₅ and fluorine with an ultraviolet laser .

Individual evidence

↑ Jeff W. Eerkens: Spectral Considerations in the Laser Isotope Separation of Uranium Hexafluoride. In: Applied Physics . A: Materials Science & Processing. Vol. 10, No. 1, 1976, pp. 15-31, doi: 10.1007 / BF00929525 .

[1] Jeff W. Eerkens: Spectral Considerations in the Laser Isotope Separation of Uranium Hexafluoride. In: Applied Physics . A: Materials Science & Processing. Vol. 10, No. 1, 1976, pp. 15-31, doi: 10.1007 / BF00929525 .