Publications

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Passive detection of special nuclear material (SNM) at long range or under heavy shielding can only be directly achieved by observing the penetrating neutral particles that it emits: gamma rays and neutrons in the MeV energy range. The ultimate SNM standoff detector system would have sensitivity to both gamma and neutron radiation, a large area and high efficiency to capture as many signal particles as possible, and good discrimination against background particles via directional and energy information. We are exploring the use of time-modulated collimators that may lead to practical gamma-neutron imaging detector systems that are highly efficient with the potential to exhibit simultaneously high angular and energy resolution. We will present results from a large standoff SNM detection demonstration using a prototype high sensitivity time encoded modulation imager. © 2011 IEEE.

An anisotropy in a scintillator's response to neutron elastic scattering interactions can in principle be used to gather directional information about a neutron source using interactions in a single detector. In crystalline organic scintillators, such as anthracene, both the amplitude and the time structure of the scintillation light pulse vary with the direction of the proton recoil with respect to the crystalline axes. Therefore, we have investigated the exploitation of this effect to enable compact, high-efficiency fast neutron detectors that have directional sensitivity via a precise measurement of the pulse shape. We report measurements of the pulse height and shape dependence on proton recoil angle in anthracene, stilbene, p-terphenyl, diphenyl anthracene (DPA), and tetraphenyl butadiene (TPB). Image reconstruction for simulated neutron sources is demonstrated using maximum likelihood methods for optimal directional sensitivity. © 2010 IEEE.

An anisotropy in a scintillator's response to neutron elastic scattering interactions can in principle be used to gather directional information about a neutron source using interactions in a single detector. In crystalline organic scintillators, such as anthracene, both the amplitude and the time structure of the scintillation light pulse vary with the direction of the proton recoil with respect to the crystalline axes. Therefore, we have investigated the exploitation of this effect to enable compact, high-efficiency fast neutron detectors that have directional sensitivity via a precise measurement of the pulse shape. We report measurements of the pulse height and shape dependence on proton recoil angle in anthracene, stilbene, p-terphenyl, diphenyl anthracene (DPA), and tetraphenyl butadiene (TPB). Image reconstruction for simulated neutron sources is demonstrated using maximum likelihood methods for optimal directional sensitivity. © 2010 IEEE.

Because of their penetrating power, energetic neutrons and gamma rays ({approx}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 new approach to fast-neutron imaging - a coded aperture neutron imaging system (CANIS). Coded aperture neutron imaging should offer a highly efficient solution for improved detection speed, range, and sensitivity. We have demonstrated fast neutron and gamma ray imaging with several different configurations of coded masks patterns and detectors including an 'active' mask that is composed of neutron detectors. Here we describe our prototype detector and present some initial results from laboratory tests and demonstrations.

Because of their penetrating power, energetic neutrons and gamma rays ({approx}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 new approach to fast-neutron imaging- a coded aperture neutron imaging system (CANIS). Coded aperture neutron imaging should offer a highly efficient solution for improved detection speed, range, and sensitivity. We have demonstrated fast neutron and gamma ray imaging with several different configurations of coded masks patterns and detectors including an 'active' mask that is composed of neutron detectors. Here we describe our prototype detector and present some initial results from laboratory tests and demonstrations.

Abstract not provided.

Abstract not provided.

An anisotropy in the response of crystalline organic scintillators such as anthracene to neutron elastic scattering interactions has been known for some time. Both the amplitude and the time structure of the scintillation light pulse vary with the direction of the proton recoil with respect to the crystalline axes. In principle, this effect could be exploited to develop compact, high-efficiency fast neutron detectors that have directional sensitivity via a precise measurement of the pulse shape. We are investigating the feasibility and sensitivity of such a detector, particularly for neutrons in the fission energy spectrum. Here we will report new measurements of the pulse shape dependence on proton recoil angle in anthracene and stilbene single crystals, for proton energies in the few MeV range. Digital pulse acquisition and processing are used to allow an exploration of different pulse shape analysis techniques.

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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Abstract not provided.