Termed Special Nuclear Material (SNM) by the Atomic Energy Act of 1954, fissile materials, such as 235U and 239Pu, are
the primary components used to construct modern nuclear weapons. Detecting the clandestine presence of SNM
represents an important capability for Homeland Security. An ideal SNM sensor must be able to detect fissile materials
present at ppb levels, be able to distinguish between the source of the detected fissile material, i.e., 235U, 239Pu, 233U or
other fission source, and be able to perform the discrimination in near real time. A sensor with such capabilities would
provide not only rapid identification of a threat but, ultimately, information on the potential source of the threat. For
example, current detection schemes for monitoring clandestine nuclear testing and nuclear fuel reprocessing to provide
weapons grade fissile material rely largely on passive air sampling combined with a subsequent instrumental analysis or
some type of wet chemical analysis of the collected material. It would be highly useful to have a noncontact method of
measuring isotopes capable of providing forensic information rapidly at ppb levels of detection. Here we compare the
use of Kr, Xe and I as "canary" species for distinguishing between 235U and 239Pu fission sources by spectroscopic
methods.
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