International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators

4-8 May 2009, Vienna

Low Dose Transmission Radiography for Detection of SNM using Monoenergetic Gamma Rays

R.C. Lanza¹, B.W. Blackburn², G. Kohse¹, R. Sheffield³, L. Waters³, and D. Williams¹

¹Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
²Integrated Defense Systems, Raytheon, Tewksbury, Massachusetts, USA
³Los Alamos National Laboratory, Los Alamos, New Mexico, USA

Corresponding Author: lanza@mit.edu

Active detection of nuclear materials (SNM) requires both the localization of the potential threat and confirmation of its nuclear properties. By selecting nuclear reactions with large positive Q values, small accelerators producing 4 to 10 MeV protons or deuterons can simultaneously produce fast neutrons and high energy (greater than 10 MeV) monoenergetic γs. A significant benefit of such monoenergetic γs lies in the greatly reduced radiation dose as compared to bremmstrahlung sources. These multiple energy monoenergetic γ rays can be used to image the material and also to confirm its nuclear properties by detection of delayed γs and neutrons from photofission. One such reaction is d(¹¹B, n)¹²C. Using 3 MeV deuterons, this reaction produces fast neutrons peaking at around 12 MeV (with a broad distribution at lower energies) and intense γ rays at 4.4 and 15.1 MeV as well as others at 10.7 and 12.7 MeV. Scaled for beam currents of 100 μA, the experimental production rates are 6 x10⁹ photons/sr/s at 4.4 MeV, 6.6 x10⁸ photons/sr/s at 15.1 MeV and 2 x10¹⁰ n/sr/s fast neutrons. Using just the 4.4 and 15.1 γs in transmission imaging, threat quantities of SNM in benign material such as 40 cm equivalent of iron may be detected in seconds with doses of 1 mrem or less. We are also investigating the development of ultra-compact cyclotrons as sources for this application.