Publications

Coded aperture neutron imaging detectors have the potential to be a powerful tool for the detection of special nuclear material at long range or under heavy shielding, using the signature of fast neutrons from spontaneous fission. We are building a prototype system using liquid scintillator cells, measuring 20'' x 2.5'' x 2.5'' each, in a reconfigurable arrangement. A cross-calibration of the observed detector data with the output of Monte Carlo simulation can both improve the sensitivity of the detector to fast neutron sources and increase the simulation accuracy, allowing the study of next-generation detector designs. Here we describe the tools and procedures developed to calibrate and simulate the detector response, including energy scale and resolution, interaction position, and gamma-neutron separation using pulse shape discrimination. Detector data and simulation are in good agreement for a test configuration. ©2009 IEEE.

Because of their penetrating power, energetic neutrons and gamma rays (>-1 MeV) offer the best possibility of detecting highly shielded or distant special nuclear material (SNM). Of these, fast neutrons offer the greatest advantage due to their very low and well understood natural background. We are investigating a wholly new approach to fast-neutron imaging - an active coded-aperture system that uses a coded mask composed of neutron detectors. The only previously demonstrated method for long-range fast neutron imaging is double-scatter imaging. Active coded-aperture neutron imaging should offer a highly efficient alternative for improved detection speed, range, and sensitivity. We will describe our detector including design considerations and present initial results from a lab prototype. ©2009 IEEE.

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The primary function of the Gamma Detector Response and Analysis Software (GADRAS) is the solution of inverse radiation transport problems, by which the configuration of an unknown radiation source is inferred from one or more measured radiation signatures. GADRAS was originally developed for the analysis of gamma spectrometry measurements. During fiscal years 2007 and 2008, GADRAS was augmented to implement the simultaneous analysis of neutron multiplicity measurements. This report describes the radiation transport methods developed to implement this new capability. This work was performed at the direction of the National Nuclear Security Administration's Office of Nonproliferation Research and Development. It was executed as an element of the Proliferation Detection Program's Simulation, Algorithm, and Modeling element.

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