A Novel Low-Dose Approach to Active Detection of Shielded High-Z Materials

  • MIT Room 24-213 24 Cambridge, MA 02142

Lt. Col. Buck Oday

MIT Nuclear Science and Engineering

One of the most significant challenges of detecting Special Nuclear Material (SNM), and particularly highly enriched uranium, is the difficulty associated with detecting radiation signatures from shielded material. The two basic approaches to identifying the presence of SNM are passive and active interrogation. Passive interrogation involves reading the signatures―which may include charged or neutral massive particles and massless particles―naturally emanating from materials. Active interrogation involves probing the material―with massive or massless particles―and subsequently looking at the natural and induced signatures radiating from the material. For both passive and active interrogation, low energy charged particles are of no use because of their short range in matter. Likewise, x-Rays and MeV energy gamma rays are of limited utility because they are easily shielded and there is an abundance of low-energy background gammas in the natural environment. Interrogation using several MeV energy gammas may offer a feasible alternative.

Mr. Oday’s research seeks to provide a proof of principle for the use of gamma lines produced from low threshold energy nuclear interactions to conduct transmission radiography to determine the presence or absence of high-Z materials shielded by low- to medium-Z materials. Specifically, he is interrogating various materials using the 4.44 MeV and 15.1 MeV gamma lines produced in the 11B(d,nγ)12C reaction. At 4.44 MeV, Compton scatter dominates in all materials and, with nearly constant electron density in matter, attenuation of this gamma line provides a measure of mass the gammas have passed through. At 15.1 MeV pair production dominates for high Z materials (proportional to Z2) and measurement of attenuation provides insight as to the presence or absence of high-Z materials. During this talk, he will provide an overview of the detection problem, technical challenges, and discuss current and future efforts to interrogate materials of various Z.