Separation of isotopes by laser excitation

Separation of isotopes by laser excitation (SILEX) is a process for enriching uranium to fuel nuclear reactors that may also present a growing nuclear weapons proliferation risk. It is strongly suspected that SILEX utilizes laser condensation repression to excite a vibrational mode of the uranium-235 isotope in uranium hexaflouride (UF₆), allowing this lighter molecule to move more rapidly to the outer rim of a gaseous jet and resist condensing compared to the heavier, unexcited ²³⁸UF₆. This differs greatly from previous methods of laser enrichment explored for their commercial prospects: one using atomic uranium (Atomic Vapor Laser Isotope Separation (AVLIS)) and another molecular method that uses lasers to dissociate a fluorine atom from ²³⁵UF₆ (Molecular Laser Isotope Separation (MLIS)), allowing the enriched product to precipitate out as a solid.

While the Australian company Silex Systems Limited is the most prominent developer of this technology (as part of the Global Laser Enrichment consortium), the acronym SILEX really only refers to a physical separation concept utilizing condensation repression that is well known and under development or being used for multiple applications around the world. Slight variations in operating parameters, equipment arrangements, lasers and their capabilities, may exist from one SILEX-type process to the next (and be called by a different name), but the physical separation concept remains the same if condensation repression is utilized, especially when compared to that used by AVLIS or MLIS.

Princeton physicist Ryan Snyder has suggested that this process may lead to the further proliferation of nuclear weapons by providing a new and increasingly accessible technological pathway and undetectable signatures (small area footprint and high energy efficiency).