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Uncovering Special Nuclear Materials by Low-energy Nuclear Reaction Imaging.

Rose PB, Erickson AS, Mayer M, Nattress J, Jovanovic I - Sci Rep (2016)

Bottom Line: Currently, the only practical approach for uncovering well-shielded special nuclear materials is by use of active interrogation using an external radiation source.We introduce a low-dose active detection technique, referred to as low-energy nuclear reaction imaging, which exploits the physics of interactions of multi-MeV monoenergetic photons and neutrons to simultaneously measure the material's areal density and effective atomic number, while confirming the presence of fissionable materials by observing the beta-delayed neutron emission.For the first time, we demonstrate identification and imaging of uranium with this novel technique using a simple yet robust source, setting the stage for its wide adoption in security applications.

View Article: PubMed Central - PubMed

Affiliation: G.W. Woodruff School of Mechanical Engineering, Nuclear and Radiological Engineering Program, Georgia Institute of Technology, Atlanta GA 30332, USA.

ABSTRACT
Weapons-grade uranium and plutonium could be used as nuclear explosives with extreme destructive potential. The problem of their detection, especially in standard cargo containers during transit, has been described as "searching for a needle in a haystack" because of the inherently low rate of spontaneous emission of characteristic penetrating radiation and the ease of its shielding. Currently, the only practical approach for uncovering well-shielded special nuclear materials is by use of active interrogation using an external radiation source. However, the similarity of these materials to shielding and the required radiation doses that may exceed regulatory limits prevent this method from being widely used in practice. We introduce a low-dose active detection technique, referred to as low-energy nuclear reaction imaging, which exploits the physics of interactions of multi-MeV monoenergetic photons and neutrons to simultaneously measure the material's areal density and effective atomic number, while confirming the presence of fissionable materials by observing the beta-delayed neutron emission. For the first time, we demonstrate identification and imaging of uranium with this novel technique using a simple yet robust source, setting the stage for its wide adoption in security applications.

No MeSH data available.


Related in: MedlinePlus

Transmission imaging of a test object placed behind 14 inch-thick borated polyethylene.(a) Photo of the uranium-containing object used for demonstration of transmission imaging. (b) Measured transmission integrated over the entire measured spectrum. (c) Effective atomic number, Zeff, reconstructed from the measured spectrum (please see Supplementary Material for details of the reconstruction). (d) Schematic of the object. 1 and 2–uranium rods with aluminum cladding, lead, 3 – tungsten, 4 and 5–lead and aluminum plates, respectively. (e) Calculated theoretical transmission of the test object for the average photon energy. (f) Calculated effective atomic number, Zeff, of the composite test object based on the known composition of the object. The indices on axes in (b,c,e and f) correspond to a step size of 25 mm in vertical direction, set by the detector pixel size (eight detectors were used in the array), and 3 mm in horizontal direction, set by the translation of the scanned object (total of 44 steps).
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f3: Transmission imaging of a test object placed behind 14 inch-thick borated polyethylene.(a) Photo of the uranium-containing object used for demonstration of transmission imaging. (b) Measured transmission integrated over the entire measured spectrum. (c) Effective atomic number, Zeff, reconstructed from the measured spectrum (please see Supplementary Material for details of the reconstruction). (d) Schematic of the object. 1 and 2–uranium rods with aluminum cladding, lead, 3 – tungsten, 4 and 5–lead and aluminum plates, respectively. (e) Calculated theoretical transmission of the test object for the average photon energy. (f) Calculated effective atomic number, Zeff, of the composite test object based on the known composition of the object. The indices on axes in (b,c,e and f) correspond to a step size of 25 mm in vertical direction, set by the detector pixel size (eight detectors were used in the array), and 3 mm in horizontal direction, set by the translation of the scanned object (total of 44 steps).

Mentions: The experimental results are in excellent agreement with a simple one-dimensional analytical model based on the Beer-Lambert Law, showing the scaling of energy-dependent transmission T(E) = exp(−(μ(E)/ρ)κ), where μ(E)/ρ is the energy-dependent mass attenuation coefficient and κ is the areal density of the measured object. Determination of the atomic number then allows the areal density to be calculated from transmission at either of the photon energies. The agreement of the measurement results with the Beer-Lambert Law analytical model that uses the known mass attenuation coefficients for a range of materials studied (Z = 13–92) illustrates the capability to provide elemental discrimination using this method even with low-resolution detectors. A limitation of a simple two-energy approach is that it cannot readily distinguish elemental mixtures from pure elements, as it measures the “effective atomic number”, Zeff. Such ambiguities may be partially resolved by use of more than two photon energies and tomographic techniques. Monoenergetic photons at other energies can be produced from a variety of other projectiles and targets. For example, gamma rays at a range of energies up to ~18 MeV could be produced using deuteron- and proton-driven nuclear reactions such as 27Al(d,nγ)28Si, 7Li(p,γ)8Be, and 19F(p,α)20Ne. Of particular interest is the possibility of using a single projectile and interchangeable or mixed targets, which could lead to convenient practical implementations. In Fig. 3, we provide an example of imaging of a uranium-containing composite object by the energetic photons produced by the 11B(d,nγ)12C source with an array of Cherenkov detectors. We used ion chambers to measure the radiation dose due to photons in the experiment shown in Fig. 3, finding the dose to be 0.36 ± 0.016 mrem hr−1 μA−1. We provide a comparison with the American National Standards Institute (ANSI) N43.14-2011 standard19, which limits the dose to potential stowaways to 500 mrem (5 mSv) per scan. The low-energy nuclear reaction source delivers a dose due to photons on the order of 0.1 mrem, conservatively assuming 3-MeV D+ beam current of 1 mA and scanning time of 1 s (imaged object moving at a speed of ~3 km/h). This calculation is based on experimentally measured dose due to photons, assuming linear scaling of dose with the accelerator current. Current methods of dose assessment in conventional x-ray scanning systems involve understanding of imaging performance. Although there is no official standard for evaluating image quality of active interrogation systems, in 2008 the ANSI published the N42.46-2008 standard20. Four standardized tests have been described therein, including spatial resolution and penetration tests, to be used for assessing the image quality of all x-ray and gamma-ray systems used for security screening. However, these tests cannot be readily applied to systems based on monoenergetic photons: while monoenergetic systems may benefit from enhanced penetration due to larger number of high energy photons, the spatial resolution can suffer if low-dose scanning is desired. Additional dedicated studies are necessary to standardize imaging quality requirements and to evaluate the associated dose. Finally, dose due to photoneutrons may become dominant if the higher energy (10–15 MeV photons) are to be used for imaging applications.


Uncovering Special Nuclear Materials by Low-energy Nuclear Reaction Imaging.

Rose PB, Erickson AS, Mayer M, Nattress J, Jovanovic I - Sci Rep (2016)

Transmission imaging of a test object placed behind 14 inch-thick borated polyethylene.(a) Photo of the uranium-containing object used for demonstration of transmission imaging. (b) Measured transmission integrated over the entire measured spectrum. (c) Effective atomic number, Zeff, reconstructed from the measured spectrum (please see Supplementary Material for details of the reconstruction). (d) Schematic of the object. 1 and 2–uranium rods with aluminum cladding, lead, 3 – tungsten, 4 and 5–lead and aluminum plates, respectively. (e) Calculated theoretical transmission of the test object for the average photon energy. (f) Calculated effective atomic number, Zeff, of the composite test object based on the known composition of the object. The indices on axes in (b,c,e and f) correspond to a step size of 25 mm in vertical direction, set by the detector pixel size (eight detectors were used in the array), and 3 mm in horizontal direction, set by the translation of the scanned object (total of 44 steps).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834544&req=5

f3: Transmission imaging of a test object placed behind 14 inch-thick borated polyethylene.(a) Photo of the uranium-containing object used for demonstration of transmission imaging. (b) Measured transmission integrated over the entire measured spectrum. (c) Effective atomic number, Zeff, reconstructed from the measured spectrum (please see Supplementary Material for details of the reconstruction). (d) Schematic of the object. 1 and 2–uranium rods with aluminum cladding, lead, 3 – tungsten, 4 and 5–lead and aluminum plates, respectively. (e) Calculated theoretical transmission of the test object for the average photon energy. (f) Calculated effective atomic number, Zeff, of the composite test object based on the known composition of the object. The indices on axes in (b,c,e and f) correspond to a step size of 25 mm in vertical direction, set by the detector pixel size (eight detectors were used in the array), and 3 mm in horizontal direction, set by the translation of the scanned object (total of 44 steps).
Mentions: The experimental results are in excellent agreement with a simple one-dimensional analytical model based on the Beer-Lambert Law, showing the scaling of energy-dependent transmission T(E) = exp(−(μ(E)/ρ)κ), where μ(E)/ρ is the energy-dependent mass attenuation coefficient and κ is the areal density of the measured object. Determination of the atomic number then allows the areal density to be calculated from transmission at either of the photon energies. The agreement of the measurement results with the Beer-Lambert Law analytical model that uses the known mass attenuation coefficients for a range of materials studied (Z = 13–92) illustrates the capability to provide elemental discrimination using this method even with low-resolution detectors. A limitation of a simple two-energy approach is that it cannot readily distinguish elemental mixtures from pure elements, as it measures the “effective atomic number”, Zeff. Such ambiguities may be partially resolved by use of more than two photon energies and tomographic techniques. Monoenergetic photons at other energies can be produced from a variety of other projectiles and targets. For example, gamma rays at a range of energies up to ~18 MeV could be produced using deuteron- and proton-driven nuclear reactions such as 27Al(d,nγ)28Si, 7Li(p,γ)8Be, and 19F(p,α)20Ne. Of particular interest is the possibility of using a single projectile and interchangeable or mixed targets, which could lead to convenient practical implementations. In Fig. 3, we provide an example of imaging of a uranium-containing composite object by the energetic photons produced by the 11B(d,nγ)12C source with an array of Cherenkov detectors. We used ion chambers to measure the radiation dose due to photons in the experiment shown in Fig. 3, finding the dose to be 0.36 ± 0.016 mrem hr−1 μA−1. We provide a comparison with the American National Standards Institute (ANSI) N43.14-2011 standard19, which limits the dose to potential stowaways to 500 mrem (5 mSv) per scan. The low-energy nuclear reaction source delivers a dose due to photons on the order of 0.1 mrem, conservatively assuming 3-MeV D+ beam current of 1 mA and scanning time of 1 s (imaged object moving at a speed of ~3 km/h). This calculation is based on experimentally measured dose due to photons, assuming linear scaling of dose with the accelerator current. Current methods of dose assessment in conventional x-ray scanning systems involve understanding of imaging performance. Although there is no official standard for evaluating image quality of active interrogation systems, in 2008 the ANSI published the N42.46-2008 standard20. Four standardized tests have been described therein, including spatial resolution and penetration tests, to be used for assessing the image quality of all x-ray and gamma-ray systems used for security screening. However, these tests cannot be readily applied to systems based on monoenergetic photons: while monoenergetic systems may benefit from enhanced penetration due to larger number of high energy photons, the spatial resolution can suffer if low-dose scanning is desired. Additional dedicated studies are necessary to standardize imaging quality requirements and to evaluate the associated dose. Finally, dose due to photoneutrons may become dominant if the higher energy (10–15 MeV photons) are to be used for imaging applications.

Bottom Line: Currently, the only practical approach for uncovering well-shielded special nuclear materials is by use of active interrogation using an external radiation source.We introduce a low-dose active detection technique, referred to as low-energy nuclear reaction imaging, which exploits the physics of interactions of multi-MeV monoenergetic photons and neutrons to simultaneously measure the material's areal density and effective atomic number, while confirming the presence of fissionable materials by observing the beta-delayed neutron emission.For the first time, we demonstrate identification and imaging of uranium with this novel technique using a simple yet robust source, setting the stage for its wide adoption in security applications.

View Article: PubMed Central - PubMed

Affiliation: G.W. Woodruff School of Mechanical Engineering, Nuclear and Radiological Engineering Program, Georgia Institute of Technology, Atlanta GA 30332, USA.

ABSTRACT
Weapons-grade uranium and plutonium could be used as nuclear explosives with extreme destructive potential. The problem of their detection, especially in standard cargo containers during transit, has been described as "searching for a needle in a haystack" because of the inherently low rate of spontaneous emission of characteristic penetrating radiation and the ease of its shielding. Currently, the only practical approach for uncovering well-shielded special nuclear materials is by use of active interrogation using an external radiation source. However, the similarity of these materials to shielding and the required radiation doses that may exceed regulatory limits prevent this method from being widely used in practice. We introduce a low-dose active detection technique, referred to as low-energy nuclear reaction imaging, which exploits the physics of interactions of multi-MeV monoenergetic photons and neutrons to simultaneously measure the material's areal density and effective atomic number, while confirming the presence of fissionable materials by observing the beta-delayed neutron emission. For the first time, we demonstrate identification and imaging of uranium with this novel technique using a simple yet robust source, setting the stage for its wide adoption in security applications.

No MeSH data available.


Related in: MedlinePlus