Stephen E. Korbly

Nuclear Resonance Fluorescence of /sup 235/U

Nuclear resonance fluorescence is a physical process that provides an isotopic-specific signature that can be used for the identification and characterization of materials. The technique involves the detection of prompt discrete-energy photons emitted from a sample which is exposed to photons in the MeV energy range. Potential applications of the technique range from detection of high explosives to characterization of special nuclear materials. One isotope of significant interest is 235U. Pacific Northwest National Laboratory and Passport Systems have collaborated to conduct measurements searching for nuclear resonance fluorescence signatures of 235U below 3 MeV using a 220 g sample of highly enriched uranium. Nine 235U resonances between 1650 and 2010 keV were identified in the preliminary analysis. Analysis of the measurement data to determine the integrated cross sections of the resonances is in progress.

Prompt neutrons from photofission and its use in homeland security applications

Photofission is the process in which a nucleus disintegrates into two daughter products after absorbing a photon. Photofission near threshold in actinides is very similar to spontaneous fission in terms of the number of emitted decay neutrons and their energy distribution. Most of the neutrons are in the ∼2 MeV energy range, and can be efficiently detected with liquid scintillator detectors. Thus, Prompt Neutrons from Photofission (PNPF) near threshold can be used as an excellent tool for the detection of actinides. Since the photofission cross section for most fissionable materials drops to near zero for incident photon energies of less than 6 MeV, a source of photons with a higher energy is needed, for example 9 MeV. At this energy interference from (γ, n) processes is minimal. Photon sources in this energy range are well suited for other non-intrusive inspection applications as well as searching for fissionable materials. Passport Systems, Inc. is currently operating a continuous wave (CW) 9 MeV electron accelerator and an array of liquid scintillator detectors to achieve this goal. Pulse shape discrimination (PSD) techniques are used determine the particle type. The remaining neutrons are also filtered through an in-house developed pileup rejection algorithm. The resulting neutron count is compared with the known background to determine the confidence level for possible shielded Special Nuclear Material identification. Initial testing of this system has been performed and the results will be presented. The results show the utility of a CW photon source as well as the ability to fuse the PNPF data with other data to reduce the dose to cargo, or scan times.

On the Search for Nuclear Resonance Fluorescence Signatures of

Nuclear resonance fluorescence is a physical process that provides an isotope-specific signature that could be used for the identification and characterization of materials. The technique involves the detection of prompt discrete-energy photons emitted from a sample that is exposed to MeV-energy photons. Potential applications of the technique range from detection of high explosives to characterization of special nuclear materials such as 235U. We conducted a pair of measurements to search for a nuclear resonance fluorescence response of 235U above 3 MeV and of 238U above 5 MeV using an 8 g sample of highly enriched uranium and a 90 g sample of depleted uranium. No new signatures were observed. The minimum detectable integrated cross section for 235U varies from 4 eV b at 3 MeV up to 120 eV b at 8 MeV.

^{235}{\rm U}

Four new technologies have been developed for use in non‐intrusive inspection systems to detect nuclear materials, explosives and contraband. Nuclear Resonance Fluorescence (NRF) provides a three dimensional image of the isotopic content of a container. NRF determines the isotopic composition of a region and specifies the isotopic structure of the neighboring regions, thus providing the detailed isotopic composition of any threat. In transmission mode, NRF provides a two dimensional projection of the isotopic content of a container, much as standard X‐ray radiography provides for density. The effective‐Z method (EZ‐3D™) uses electromagnetic scattering processes to yield a three‐dimensional map of the effective‐Z and the density in a container. The EZ‐3D™ method allows for a rapid discrimination based on effective Z and mass of materials such as those with high Z, as well as specifying regions of interest for other contraband. The energy spectrum of prompt neutrons from photon induced fission (PNPF) provid...

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Pacific Northwest National Laboratory and Passport Systems have collaborated to perform nuclear resonance fluorescence (NRF) experiments using several high quality high-explosive simulant samples. These measurements were conducted to determine the feasibility of finding and characterizing high explosive material by NRF interrogation. Bremstrahlung photon beams, produced from electron beams of 5.1, 5.3, 8.3, 9 and 10 MeV, irradiated the samples. Gamma-rays emitted from the samples were detected using high-purity germanium detectors. Nitrogen-to-carbon ratios of the high-explosive simulants were extracted from the 5.1 and 5.3 MeV data and compare favorably with accepted values. Analysis of the 8, 9 and 10 MeV data is in progress; preliminary isotopic comparisons within the samples are consistent with the expected results.

^{238}{\rm U}

In response to the US Department of Homeland Security (DHS) Domestic Nuclear Detection Offices (DNDO) Small Business Innovative Research (SBIR), Phase 12.1 solicitation, Passport Systems, Inc. of Billerica, MA has demonstrated the feasibility of integrating a COTS Inertial Measurement Unit (IMU) with a portable radiation detector for improved radiation source search capabilities. The SBIR Phase I feasibility study integrated both the necessary hardware and algorithms and verified the utility of providing this new capability to an operator in search scenarios. Advanced algorithms combining IMU data with radiation measurements constrained source location and increased the efficacy of the search mission. An overview of the SBIR Phase I program will provide: 1) a description of the hardware and algorithm integration; 2) a summary of the expected system benefits; and 3) a review of the proof-of-concept demonstration developed during the program.

Above 3 MeV

In response to the Domestic Nuclear Detection Offices (DNDO) BAA 09-102 Passport Systems, Inc. of Billerica, MA has developed and tested a prototype system of networked portable spectroscopic radiation detectors designed to improve the detection, localization, and identification of potential radiological threats. A system of this nature is primarily targeted to situations where it is not feasible to direct traffic through portal radiation detection systems, e.g. large events, search team objectives, etc. The capability to intelligently network individual portable detectors and fuse their data using advanced algorithms and COTS hardware has been shown within this program to significantly increase the effectiveness of an assortment of portable radiation detectors in a variety of NORM (naturally occurring radioactive material) backgrounds. An overview of current work will be provided in two parts: 1) A review of the system design, including trade space analysis, of both the hardware and algorithmic components; and 2) Presentation of data and results to date focusing on the improvement afforded by the networked data fusion.

Imaging and Radiography with Nuclear Resonance Fluorescence and Effective-Z (EZ-3D) Determination; SNM Detection Using Prompt Neutrons from Photon Induced Fission

Nuclear resonance fluorescence is a physical process that provides an isotope-specific signature that could be used for the identification and characterization of materials. The technique involves the detection of prompt discrete-energy photons emitted from a sample that is exposed to photons in the MeV energy range. Potential applications of the technique range from detection of high explosives to characterization of special nuclear materials such as 235U. Pacific Northwest National Laboratory and Passport Systems have collaborated to conduct a a pair of measurements to search for a nuclear resonance fluorescence response of 235U above 3 MeV and of 238U above 5 MeV using an 8 g sample of highly enriched uranium and a 90 g sample of depleted uranium. No new signatures were observed. The minimum detectable integrated cross section for 235U is presented.

Nuclear resonance fluorescence measurements of high explosives

Pacific Northwest National Laboratory and Passport Systems have collaborated to conduct measurements to search for a nuclear resonance fluorescence response of 235U from 3 to 5 MeV using an 8 g sample of highly enriched uranium. These new measurements complement previously reported measurements below 3 MeV. Preliminary analysis indicates that no strong resonances exist for 235U in this energy range. A second set of measurements focused on a signature search in the 5 to 10 MeV range is still under analysis.

Integration of Inertial Measurement data for improved localization and tracking of radiation sources

A robust network of distributed sensors has been proposed in response to the Radiation Awareness and Interdiction Network (RAIN) Broad Agency Announcement (BAA) issued by DHS/DNDO in March of 2014. The testbed system is designed to detect, track, and identify potential threatening radiation sources in moving vehicles without interrupting the flow of traffic in typical highway scenarios. The algorithmic basis for the system depends on a number of data fusion methodologies to optimally combine and exploit multi-sensor, multi-modal data. Specifically, data-level fusion of radiation measurements is being used to enhance detection and identification of radiation sources, while extracted feature-level data from auxiliary video sensors is used both to improve computational speed and accuracy as well as provide operationally relevant source attribution information. An overview of the current development work will be provided in two parts: 1) A theoretical description of the data fusion algorithms and their expected utility will be provided; and 2) Performance results from both simulated and real measurements will be used to demonstrate the efficacy of a system using the proposed data fusion algorithms. The expected value of the testbed system using the advanced algorithms will also be discussed.