New York, N.Y., Sept. 10, 2003 - One nightmare scenario: a terrorist dirty bomb is detonated in a major metropolitan area. Everyone's first question is "Who did it?".
One piece of the puzzle that would give law enforcement officials a head start in their search for potential suspects would be an accurate description of what radioactive materials are contained in the bomb debris. Standard isotope identification technology is relatively slow; the process can take 24 hours or more. Now a team of Los Alamos National Laboratory scientists has developed a new quick screening methodology to identify isotopes in dirty bomb debris, a procedure that can yield initial data in as few as six hours.
Developed by Bennie Martinez and colleagues from the Laboratory's Chemistry Division, the new procedure will be presented at the 2003 American Chemical Society meeting today, at the Javits Convention Center, New York, N.Y.
Utilizing standard chemical analysis the Los Alamos team came up with a unique combination of procedures that extract and identify radionuclides from fused soils and rock, likely the most common constituents in bomb debris. Other ingredients might include concrete and asphalt residues, metal fragments, plastics and glass-anything present in a populated urban setting.
In one possible scenario, the bomb debris would be initially gathered and delivered to a rapidly dispatched mobile laboratory. At the outset of analysis the sample is pulverized into a powder in a micro-mill, the radionuclides are leached and later dissolved in nitric acid. The separation takes place in the liquid-liquid phase of the procedure using iso-octyl acid phosphate (IOAP) or di-2-ethyl hexyl phosphoric acid (D2EHPA), which is basically a kind of oil and water separation technique where the two chemicals are mixed with the nitric acid solution, along with the bomb debris in a gyrorotary shaker then left motionless. As the chemicals separate from the nitric acid solution the radionuclide constituents remain with the IOAP or D2EHPA and the rest of the bomb debris remains in the nitric acid solution.
The radionuclides in solution are then stippled-tiny dots of the solution are placed on a platinum disk-and flamed over a Bunsen burner to evaporate out the liquids. The disk is then place in an alpha spectrometer where the radionuclides are finally identified.
"We have achieved a result with fair to good resolution using very few chemicals in a quick turnaround time with a minimum of steps required in the process," said Martinez. "This procedure appears to be faster and simpler than the standard ion exchange/electrodeposition method. There are shortcomings in this screening methodology as compared to ion exchange, but what we were looking for was fast results that are reasonably accurate and relatively easy to obtain, and we did that."
Initial experiments used "cold" or non-radioactive vitrified, glass-like soils spiked with known quantities of radionuclides and low-level vitrified volcanic tuff containing picocurie levels of radionuclides as stand-ins for the bomb debris. Utilizing both materials, the new screening methodology was able to identify and characterize Plutonium-239, Uranium-238, Americium-241, Curium-244 and Neptunium-237.
"It's clear the method can identify a variety of radionuclides that might be present in dirty bomb debris," said Martinez. "Since the method is fairly simple and uses a minimum of equipment, we believe it could be forward deployed and could provide early data to law enforcement and others following a terrorist event. We want to help officials close in on the culprits as fast as possible."
Martinez worked alongside Donald Dry, Doug Ware, Robert Roback and Malcolm Fowler of the Isotope and Nuclear Chemistry Group and George Brooks, Ed Gonzales and Claudine Armenta of the Analytical Chemistry Sciences Group, both groups are part of Los Alamos National Laboratory's Chemistry Division.
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