ARI-MA: Nuclear Materials Detection via Time-Encoded Differential Absorption and/or Differential Fluorescence

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The research objective of this award is to demonstrate and evaluate the use of differential absorption and differential fluorescence for the detection of fissionable nuclear materials concealed by terrorists in shipping containers, road vehicles, aircraft and ships. Differential absorption and fluorescence have long been used effectively at optical and x-ray wavelengths to identify materials and structures that would otherwise be undetectable due to the higher levels of absorption or fluorescence by the materials in which the structures of interest are embedded. But there has previously been no practical means available to extend this technique to the high photon energies needed to distinguish special nuclear materials from the non-nuclear materials and radiation shielding relied on by terrorists to conceal the shipment of the special nuclear materials of concern. In this award we will investigate the use of inverse Compton scattering employing a sequence of optical pulses of varying wavelengths to generate a matching sequence of intense, collimated gamma ray pulses of differing energies identifiable by the time windows in which these pulses are detected to determine the energy dependence of the absorption or fluorescence of the materials through which these pulses pass. By these powerful but simplified means, the presence of special nuclear materials can be identified ? even at low concentrations ? by the unique energy-dependence of their absorption and/or fluorescence. If successful, this research will (1) validate a new cost-effective means for detection of these nuclear materials, (2) provide the student and postdoctoral training needed to help establish the manpower base needed to implement these techniques, and (3) contribute to the broader development of these and related techniques to the parallel applications in science, medicine and industry.