A relatively new technology for enriching uranium known as “Separation of Isotopes by Laser Excitation” or SILEX is described in some fresh detail in a recent Los Alamos paper (pdf).
SILEX, developed in 1992 by Australian scientists, is the rarest of birds in U.S. classification policy: It is privately generated information that is nevertheless classified by the U.S. government.
Ordinarily, information must be owned or controlled by the government in order to be eligible for classification in the first place. But under the peculiar terms of the Atomic Energy Act, the government may impose classification on “all” information concerning nuclear weapons and related matters that has not been previously declassified.
Since the new SILEX technology has never been declassified, it is ipso facto classified, despite the fact that it was generated by private (and foreign) researchers. It is the only known case in which the Atomic Energy Act has been used in this constitutionally questionable manner. (See Secrecy News, 06/26/01).
Unclassified details of the SILEX process, which uses pulsed lasers to selectively excite uranium hexafluoride molecules containing uranium-235, are presented in “Enrichment Separative Capacity for SILEX” by John L. Lyman, Los Alamos National Laboratory, LA-UR-05-3786 (thanks to WT).