Neutron Interrogation System Using High Gamma Ray Signature to Detect Contraband Special Nuclear Materials in Cargo PDF Download

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A system for inspecting cargo for the presence of special nuclear material. The cargo is irradiated with neutrons. The neutrons produce fission products in the special nuclear material which generate gamma rays. The gamma rays are detecting indicating the presence of the special nuclear material.

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The goal of the work reported here is to develop a concept for an active neutron interrogation system that can detect small targets of SNM contraband in cargo containers, roughly 5 kg HEU or 1 kg Pu, even when well shielded by a thick cargo. It is essential that the concept be reliable and have low false-positive and false-negative error rates. It also must be rapid to avoid interruption of commerce, completing the analysis in minutes. A new radiation signature unique to SNM has been identified that utilizes high-energy (E{sub [gamma]} = 3-7 MeV) fission product [gamma]-ray emission. Fortunately, this high-energy [gamma]-ray signature is robust in that it is very distinct compared to normal background radiation where there is no comparable high-energy [gamma]-ray radiation. Equally important, it has a factor of 10 higher yield than delayed neutrons that are the basis of classical interrogation technique normally used on small unshielded specimens of SNM. And it readily penetrates two meters of low-Z and high-Z cargo at the expected density of H"0.5 gm/cm3. Consequently, we expect that in most cases the signature flux at the container wall is at least 2-3 decades more intense than delayed neutron signals used historically and facilitates the detection of SNM even when shielded by thick cargo. Experiments have verified this signature and its predicted characteristics. However, they revealed an important interference due to the activation of 16O by the 16O(n, p)16N reaction that produces a 6 MeV [gamma]-ray following a 7-sec [beta]-decay of the 16N. This interference is important when irradiating with 14 MeV neutrons but is eliminated when lower energy neutron sources are utilized since the reaction threshold for 16O(n, p)16N is 10 MeV. The signature [gamma]-ray fluxes exiting a thick cargo can be detected in large arrays of scintillation detectors to produce useful signal count rates of 2-4 x 104 cps. That is high enough to quickly identify SNM fission by its characteristic high energy [gamma]-ray emission and characteristic fast decay time. Fortunately, the fission product [gamma]-radiation decays with a distinctive T12 = 20-30 sec lifetime that is well matched to cargo scan speeds of about one minute per container. Experimental characterization of the {gamma}-ray fluxes exiting thick cargos has not yet been undertaken. The work reported here leads to definite requirements for the interrogation neutron source that can be met with neutron commercially available source technology. A small (6-20 ft) deuteron accelerator producing about H"1 mA, 2-5 MeV deuteron beam on a deuterium or beryllium target is required. Neutrons produced by such an accelerator are kinematically collimated in the forward direction, reducing shielding requirements while increasing the neutron flux on target to meet the intensity requirement even when there is thick intervening cargo. In addition, this technology provides a very penetrating beam in the energy range 4-8 MeV while remaining below the oxygen activation threshold. Maximum counting statistics and lowest error rates in the identification occur when the beam is pulsed with a 50 % duty cycle. The period for this pulsing must be comparable to the half-lives of the species that make up the signature, i.e. 10-60 sec. This is readily achieved with commercially available equipment and is well suited to rapid scanning of cargo containers.

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The goal of the work reported here is to develop a concept for an active neutron interrogation system that can detect small targets of SNM contraband in cargo containers, roughly 5 kg HEU or 1 kg Pu, even when well shielded by a thick cargo. It is essential that the concept be reliable and have low false-positive and false-negative error rates. It also must be rapid to avoid interruption of commerce, completing the analysis in minutes.

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Languages : en
Pages : 10

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A recently developed neutron diagnostic probe system has the potential to satisfy a significant number of van-mobile and fixed- portal requirements for nondestructive verification of sealed munitions and detection of contraband explosives and drugs. The probe is based on a unique associated-particle sealed-tube neutron generator (APSTNG) that interrogates the object of interest with a low-intensity beam of 14-MeV neutrons generated from the deuterium-tritium reaction and that detects the alpha-particle associated with each neutron. Gamma-ray spectra of resulting neutron inelastic scattering and fission reactions identify nuclides associated with all major chemicals in chemical warfare agents, explosives, and drugs, as well as many pollutants and fissile and fertile special nuclear material. Flight times determined from determined from detection times of the gamma-rays and alpha-particles yield a separate tomographic image of each identified nuclide. The APSTNG also forms the basis for a compact fast-neutron transmission imaging system that can be used along with or instead of the emission imaging system; a collimator is not required since scattered neutrons are removed by ''electronic collimation'' (detected neutrons not having the proper flight time to be uncollided are discarded). The small and relatively inexpensive APSTNG exhibits high reliability and can be quickly replaced. Proof-of-concept experiments have been performed under laboratory conditions for simulated nuclear and chemical warfare munitions and for explosives and drugs.

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Author: National Research Council
Publisher: National Academies Press
ISBN: 030906449X
Category : Transportation
Languages : en
Pages : 56

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A major goal of the Federal Aviation Administration (FAA), and now the Transportation Security Administration (TSA), is the development of technologies for detecting explosives and illegal drugs in freight cargo and passenger luggage. One such technology is pulsed fast neutron analysis (PFNA). This technology is based on detection of signature radiation (gamma rays) induced in material scanned by a beam of neutrons. While PFNA may have the potential to meet TSA goals, it has many limitations. Because of these issues, the government asked the National Research Council to evaluate the potential of PFNA for airport use and compare it with current and future x-ray technology. The results of this survey are presented in "Assessment of the Practicality of Pulsed Fast Neutron Analysis for Aviation Security." A broad range of detection methods and test results are covered in this report. Tests conducted as of October 2000 showed that the PFNA system was unable to meet the stringent federal aviation requirements for explosive detection in air cargo containers. PFNA systems did, however, demonstrate some superior characteristics compared to existing x-ray systems in detecting explosives in cargo containers, though neither system performed entirely satisfactorily. Substantial improvements are needed in the PFNA detection algorithms to allow it to meet aviation detection standards for explosives in cargo and passenger baggage. The PFNA system currently requires a long scan time (an average of 90 minutes per container in the prototype testing in October 2000), needs considerable radiation shielding, is significantly larger than current x-ray systems, and has high implementation costs. These factors are likely to limit installation at airports, even if the detection capability is improved. Nevertheless, because PFNA has the best potential of any known technology for detecting explosives in cargo and luggage, this book discusses how continued research to improve detection capabilities and system design can best be applied for the airport environment.

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Languages : en
Pages : 47

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A program of simulations and validating experiments was utilized to evaluate a concept for neutron interrogation of commercial cargo containers that would reliably detect special nuclear material (SNM). The goals were to develop an interrogation system capable of detecting a 5 kg solid sphere of high-enriched uranium (HEU) even when deeply embedded in commercial cargo. Performance goals included a minimum detection probability, P{sub d} e"95%, a maximum occurrence of false positive indications, P{sub fA} d"0.001, and maximum scan duration of t d"1 min. The conditions necessary to meet these goals were demonstrated in experimental measurements even when the SNM is deeply buried in any commercial cargo, and are projected to be met successfully in the most challenging cases of steel or hydrocarbons at areal density [rho]L d"150 g/cm2. Optimal performance was obtained with a collimated ([Delta][Theta] = ± 15{sup o}) neutron beam at energy E{sub n} = 7 MeV produced by the D(d, n) reaction with the deuteron energy E{sub d} = 4 MeV. Two fission product signatures are utilized to uniquely identify SNM, including delayed neutrons detected in a large array of polyethylene moderated 3He proportional counters and high energy [beta]-delayed fission product [gamma]-radiation detected in a large array of 61 x 61 x 25 cm3 plastic scintillators. The latter detectors are nearly blind to normal terrestrial background radiation by setting an energy threshold on the detection at E{sub min} e"3 MeV. Detection goals were attained with a low beam current (I{sub d} = 15-65 [mu]A) source up to [rho]L = 75 g/cm2 utilizing long irradiations, T = 30 sec, and long counting times, t = 30-100 sec. Projecting to a higher beam current, I{sub d} e"600 [mu]A and larger detector array the detection and false alarm goals would be attained even with intervening cargo overburden as large as [rho]L d"150 g/cm2. The latter cargo thickness corresponds to 8 ft of hydrogenous or metallic cargo at the highest density allowed by the weight limit of the container. Simulations support the efficacy of this technique in the most challenging cases and experimental measurements are shown validating these predictions. Signal and background levels have been assessed and utilized to predict error rates due to false positive and false negative results. The laboratory system demonstrates the ability to detect HEU in amounts as small as m e"250 g buried in the middle of a maximum density cargo and to do so with error rates that meet the goals given above. Higher beam current allows reliable SNM detection in shorter irradiation and/or counting times and with more challenging cargo threat scenarios.

Author: Igor Jovanovic
Publisher: Springer
ISBN: 3319744674
Category : Technology & Engineering
Languages : en
Pages : 366

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This volume constitutes the state-of-the-art in active interrogation, widely recognized as indispensable methods for addressing current and future nuclear security needs. Written by a leading group of science and technology experts, this comprehensive reference presents technologies and systems in the context of the fundamental physics challenges and practical requirements. It compares the features, limitations, technologies, and impact of passive and active measurement techniques; describes radiation sources for active interrogation including electron and ion accelerators, intense lasers, and radioisotope-based sources; and it describes radiation detectors used for active interrogation. Entire chapters are devoted to data acquisition and processing systems, modeling and simulation, data interpretation and algorithms, and a survey of working active measurement systems. Active Interrogation in Nuclear Security is structured to appeal to a range of audiences, including graduate students, active researchers in the field, and policy analysts. The first book devoted entirely to active interrogation Presents a focused review of the relevant physics Surveys available technology Analyzes scientific and technology trends Provides historical and policy context Igor Jovanovic is a Professor of Nuclear Engineering and Radiological Sciences at the University of Michigan and has previously also taught at Penn State University and Purdue University. He received his Ph.D. from University of California, Berkeley and worked as physicist at Lawrence Livermore National Laboratory. Dr. Jovanovic has made numerous contributions to the science and technology of radiation detection, as well as the radiation sources for use in active interrogation in nuclear security. He has taught numerous undergraduate and graduate courses in areas that include radiation detection, nuclear physics, and nuclear security. At University of Michigan Dr. Jovanovic is the director of Neutron Science Laboratory and is also associated with the Center for Ultrafast Optical Science. Anna Erickson is an Assistant Professor in the Nuclear and Radiological Engineering Program of the G.W. Woodruff School of Mechanical Engineering at Georgia Institute of Technology. Previously, she was a postdoctoral researcher in the Advanced Detectors Group at Lawrence Livermore National Laboratory. Dr. Erickson received her PhD from Massachusetts Institute of Technology with a focus on radiation detection for active interrogation applications. Her research interests focus on nuclear non-proliferation including antineutrino analysis and non-traditional detector design and characterization. She teaches courses in advanced experimental detection for reactor and nuclear nonproliferation applications, radiation dosimetry and fast reactor analysis.

Author: P. Kerr
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Languages : en
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We are developing a new active interrogation system based on a kinematically focused low energy neutron beam. The key idea is that one of the defining characteristics of SNM (Special Nuclear Materials) is the ability for low energy or thermal neutrons to induce fission. Thus by using low energy neutrons for the interrogation source we can accomplish three goals, (1) Energy discrimination allows us to measure the prompt fast fission neutrons produced while the interrogation beam is on; (2) Neutrons with an energy of approximately 60 to 100 keV do not fission 238U and Thorium, but penetrate bulk material nearly as far as high energy neutrons do and (3) below about 100keV neutrons lose their energy by kinematical collisions rather than via the nuclear (n,2n) or (n, n') processes thus further simplifying the prompt neutron induced background. 60 keV neutrons create a low radiation dose and readily thermal capture in normal materials, thus providing a clean spectroscopic signature of the intervening materials. The kinematically beamed source also eliminates the need for heavy backward and sideway neutron shielding. We have designed and built a very compact pulsed neutron source, based on an RFQ proton accelerator and a lithium target. We are developing fast neutron detectors that are nearly insensitive to the ever-present thermal neutron and neutron capture induced gamma ray background. The detection of only a few high energy fission neutrons in time correlation with the linac pulse will be a clear indication of the presence of SNM.

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Languages : en
Pages : 60

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Shielded special nuclear material (SNM) is very difficult to detect and new technologies are needed to clear alarms and verify the presence of SNM. High-energy photons and neutrons can be used to actively interrogate for heavily shielded SNM, such as highly enriched uranium (HEU), since neutrons can penetrate gamma-ray shielding and gamma-rays can penetrate neutron shielding. Both source particles then induce unique detectable signals from fission. In this LDRD, we explored a new type of interrogation source that uses low-energy proton- or deuteron-induced nuclear reactions to generate high fluxes of mono-energetic gammas or neutrons. Accelerator-based experiments, computational studies, and prototype source tests were performed to obtain a better understanding of (1) the flux requirements, (2) fission-induced signals, background, and interferences, and (3) operational performance of the source. The results of this research led to the development and testing of an axial-type gamma tube source and the design/construction of a high power coaxial-type gamma generator based on the 11B(p, [gamma])12C nuclear reaction.