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What is laser aided decontamination, light aided decontamination, or LAD?

High energy lasers, either continuous or pulsed, can be used to remove surface contamination from virtually any solid surface. Contaminants removed may include organic or inorganic materials, and the most potentially valuable application is arguably the removal of radioactive surface contamination. This has been given the acronym of LAD for "Laser" or "Light Aided Decontamination". (Note that high energy light sources other than lasers have also been demonstrated to be effective.)

A laser beam hitting a surface can bring the surface temperature to 2,000 degrees F or higher within microseconds. Any organic materials (such as in paint) are vaporized, decompose in the plasma formed, and are ejected (violently) from the surface. Any inorganic debris ejected from the surface can be collected using an integrated vacuum system and appropriate filters. The amount of surface material removed and the depth of penetration of the beam are a function of the physical properties of the surface (metal, concrete, wood) the laser energy level, the type of laser/light used (wavelength), and the scan rate.

The controls of such a system can be so fine that one layer of paint can be remove to expose a prior layer of a different color.

Because of the inherent dangers in such a high energy beam, all operations should be computer/robot controlled. Typical use involves controlled raster scanning, similar to the scan used on a television screen. Thus, operations can be visually previewed by scanning or 'lighting-up' the surface with a low energy laser to verify the correct coverage area before initiating the high energy process.

There are two other attractive features that can be designed into a laser decon system. First, by using a pulsed beam or by interrupting the continuous beam, the light being emitted by the hot surface plasma can be read spectroscopically, revealing the elemental species present in the ejecta. Thus with a feedback loop, the system can scan the surface repeatedly until it is "cleaned" of selected target contaminants.

Second, in using a laser with continuous power rating of 2000 watts or more, an operator can switch from a "gentle" surface Decon operation to cutting 1/2 inch steel (for example) at the rate of 20 inches per minute (or other materials at equivalent rates). This permits the cleaning of equipment followed by dissecting it into small disposable sections, without the necessity of retooling the operation.

Note: This very attractive Decon technology has been rejected in some US government applications because of supposed "safety" concerns. Those concerns came from poorly conceived testing with hand held rather than robotic end effectors and without the use of computer controls. The operator flinched during the test, which resulted in the beam going in unintended directions, the accidental cutting of an oxygen line, and a resultant fire (metal at 2,000 degrees in an oxygen atmosphere WILL burn remarkably well.) Conversely automobile manufacturers have used such lasers for over two decades for many cutting and welding operations, computer controlled, with no major adverse effects.

Sources/References:

Dann J. Flesher and Rand D. Miller, Light Aided Decontamination 1996 (LAD), Surface Cleaning, Cutting, and Welding With Light: A Now Technology, WHC-SA-3110-S, Westinghouse Hanford Company

John F. Asmus, UCSD, and D.J.Flesher, WHC, Coating Ablation and Surface Modification by Pulsed Light Radiation, Surface and Coatings Technology, 62 (1993) Institute for Pure and Applied Physical Sciences, University of California, San Diego/La Jolla. California and Westinghouse Hanford Company, Richland Washington, 1993.

Dann J. Flesher, Light Aided (Laser) Decontamination, WHC-SD-WM-TI-518, Westinghouse Hanford Company, Richland, Washington, June 1992.

N. Scott Cannon and D. J. Flesher, Lasers for the Radioactive Decontamination of Concrete, presented at: 16 th International Conference on Lasers and Applications, LASERS '93, Lake Tahoe, NV, December 1993, WHC-SA-2116-FP, Westinghouse Hanford Company, Richland WA, October 1993

http://en.wikipedia.org/wiki/Nuclear_decommissioning