Long-range SNM detection using alternative signatures

"Increasing the distance for standoff detection of nuclear materials, beyond that capable with direct radiation detection, using alternative signatures, such as the concentration of ionization in the surrounding atmosphere, improves the ability to locate, track and monitor this material. Ionizing radiation generates free elections, ions, and exited states in the nearby atmosphere, even when the sources are shielded, which can be detected from a distance. The power-law decrease in the signal as a function of distance, low signal levels and the activity of the source limit the measurement of the unamplified excitation and ionization signatures from the source. The Phase-1 effort will evaluate different approaches for detecting exited states or ionization created by ionizing radiation from nuclear materials. A most promising approach, developed at the University of Michigan, involves mapping the concentration of ions detected by the generation of a plasma in the air by scanning a pulsed laser whose power is below the threshold required to ionize air without charge from ionizing radiation. Extending the range of the ionizing laser in Phase-1 demonstrates the feasibility of this approach. The Phase-2 effort will design, construct, and test a prototype system."