Molecular laser isotope separation
(MLIS molecular laser isotope Abbreviation for separation, German molecular laser isotope separation ) is a method of laser isotope separation, in which the isotopes are present in molecular form and selectively dissociated by laser radiation of highest frequency stability and narrow bandwidth. With the use of nuclear energy from uranium, the method used for enrichment of the fissile isotope 235U by thermal neutrons.
Another type of laser enrichment is the atomic method AVLIS. Both methods have attained any great technical significance.
Description
Uranium enrichment using the molecular laser process one goes from the gaseous compound uranium hexafluoride ( UF6) from. As with the atomic processes rely on the isotope shift, that is the fact that even in the level scheme of molecular vibrations vary the energy levels of the various isotopes slightly. By irradiation with laser radiation in the mid-infrared can be achieved that certain molecular vibration levels are selectively excited and thereby dissociate only the molecules of this isotope, i.e., separated into two fragments.
The selective excitation would be relatively uncritical when the UF6 molecules all were in the respective ground state. However, this basic state is busy at room temperature on the basis of the Boltzmann distribution of only about 1%. The observed absorption spectrum is consequently a mixture of transitions between different excited vibrational and rotational energy levels, which are superimposed on the lines of the various isotopes. The width of the absorption band is so much larger than the isotope, which greatly reduces the selectivity. One must therefore go to lower temperatures. At 55 K (about -220 ° C) the occupation of the ground state reaches a value of about 90 %.
Irradiation technology, the proceeds in two stages. The UF6 gas ( for example, a frequency stabilized laser carbon dioxide ) is first selectively excited with an infrared laser and then dissociated with an ultraviolet laser UF5 and fluorine.