Atomic vapor laser isotope separation

AVLIS (atomic vapor laser isotope separation) is the acronym for a method of laser isotope separation, where the isotopes are first converted into atomic form in the vapor phase.

With the use of nuclear energy of uranium ( uranium enrichment), the method used for the enrichment of the thermally fissile 235U isotope. Another type of laser enrichment is the molecular processes (see MLIS). Both methods have attained any great technical significance.

The basic principle of the AVLIS process is that the atoms of isotope are selectively ionized mixture (eg uranium isotopes). After ionization of an isotope ( U235 ), it may of the non-ionized atoms of the other isotope ( 238U ) are separated by acceleration in an electric field. The method was originally developed at Lawrence Livermore National Laboratory (USA). A similar, persecuted in France variant is named SILVA ( Séparation Isotopique par laser de la Vapeur Atomique d' Uranium ).

For atoms with mass numbers higher interactions between the valence electrons lead to a variety of splitting of the energy levels and make the energy-level diagram very confusing. Uranium has six valence electrons. According to complexity of the level scheme up today about 900 identified levels.

Wherein the developed Livermore laser separation method of uranium is first vaporized in a oven at 2500 K. The existing in the vapor atomic 235U is excited by a tuned to specific wavelengths of 235U - spectrum laser light beam into the continuum. The 235U gives off an electron and can be drawn off as ions on a negatively biased metallic collector. The isotope 235U and 238U between results from the different size of the two nuclei and is about 0.005 nm at a wavelength around 600 nm, the tuning of the laser must therefore be very precise and constant.

In terms of apparatus, the method of the laser system and the separator system. The laser system comprising the tunable dye laser to the desired frequency, which are pumped with copper vapor lasers. The separator system consists of the evaporator furnace, in which the metallic uranium is converted into the vapor phase, and the panels on which the positively charged 235U ions reflected.

A particularly critical point is the vapor density in the fan-shaped atomic beam exiting the furnace. The excitation energy and the ion charge can in fact be easily transferred by collisions from one atom to the other, which affects the separation effect. The uranium vapor density should not exceed a value of about 1013/cm ³. The density limitation due to charge exchange can reduce, if one extracts the ions with a strong electric field from the interaction zone. A further difficulty arises from the thermal ionization of uranium in a hot oven. If only a fraction of 0.1% of 238U is ionized, the 235U/238U-Verhältnis in the final product can not exceed the value of 5, even if 70% of the ionized 235U.