Limits...
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

Illustration of the imaging method using a low-energy nuclear reaction radiation source.(a) Low-energy nuclear reaction imaging relies upon the source of monochromatic photons via a nuclear reaction between an ion accelerated to MeV-scale energy and a target. Gamma rays at discrete energies are produced from nuclear excited states of the product nucleus, with some reactions also producing neutrons. The collimated, penetrating radiation from the nuclear reaction source is used to perform transmission radiography of a shielded object, while neutron/gamma discriminating detectors detect the signature of nuclear fission. (b) Photon spectrum from the 11B(d,nγ)12C reaction measured with a LaBr scintillation detector. The detector is capable of measurement of the 15.1 MeV peak despite of small crystal size. It is also able to resolve the full energy peaks (labeled as “f”) and single (“s”) and double (“d”) escape peaks. Also shown are “j” and “k” peaks corresponding to other nuclear transitions in the target. (c) Energy-dependent attenuation for several elements (4.438 MeV and 15.1 MeV gamma energies from the 11B(d,nγ)12C reaction are shown as dashed lines).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4834544&req=5

f1: Illustration of the imaging method using a low-energy nuclear reaction radiation source.(a) Low-energy nuclear reaction imaging relies upon the source of monochromatic photons via a nuclear reaction between an ion accelerated to MeV-scale energy and a target. Gamma rays at discrete energies are produced from nuclear excited states of the product nucleus, with some reactions also producing neutrons. The collimated, penetrating radiation from the nuclear reaction source is used to perform transmission radiography of a shielded object, while neutron/gamma discriminating detectors detect the signature of nuclear fission. (b) Photon spectrum from the 11B(d,nγ)12C reaction measured with a LaBr scintillation detector. The detector is capable of measurement of the 15.1 MeV peak despite of small crystal size. It is also able to resolve the full energy peaks (labeled as “f”) and single (“s”) and double (“d”) escape peaks. Also shown are “j” and “k” peaks corresponding to other nuclear transitions in the target. (c) Energy-dependent attenuation for several elements (4.438 MeV and 15.1 MeV gamma energies from the 11B(d,nγ)12C reaction are shown as dashed lines).

Mentions: One of the key characteristics of the low-energy nuclear reaction source is that the energies of the emitted gamma rays are governed by the nuclear structure rather than the detailed characteristics of the interaction region and interacting particles, as is the case with bremsstrahlung and inverse Compton scattering. The concept of the detection and imaging approach employed in this work is illustrated in Fig. 1a. The 11B(d,nγ)12C reaction is driven by a radio-frequency quadrupole accelerator, which produces a 3-MeV D+ beam with a typical current on the order of tens of μA. The D+ beam is incident onto a natural boron target placed inside the vacuum system of the accelerator. In addition to emission of an energetic neutron, this exothermic reaction efficiently populates the high-energy excited states of the product 12C nucleus, as has been shown in prior work15. The 12C nucleus subsequently emits gamma rays, with the most prominent yields at 4.438 MeV (2+ → 0+) and 15.1 MeV (1+ → 0+). Based on experimental measurements and independently characterized intrinsic efficiency of the detectors used, the gamma ray yields in our experiments were 5.3 × 107 s−1 μA−1 and 6.2 × 106 s−1 μA−1 at 4.438 MeV and 15.1 MeV, respectively; the fast neutron yield was 1.3 × 109 s−1 μA−1. The 12C nucleus can also be excited to produce gamma rays by another reaction, 12C(p,p’)12C, which does not produce neutrons, but relatively high energies (~18 MeV) of the incident protons are needed to exceed the reaction threshold. In our experiment with the 11B(d,nγ)12C target, the emitted radiation is collimated into a fan beam using concrete shielding; the produced neutrons can also be efficiently removed from the beam using borated polyethylene without significantly affecting the high-energy photon flux. The examined object can be placed a variety of distances from the source, with the closest practical distance of 100 cm in our experiment. The details of experimental setup including facilities, imaging objects, detector array positions, and operating characteristics can be found in Supplementary Materials.


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

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

Illustration of the imaging method using a low-energy nuclear reaction radiation source.(a) Low-energy nuclear reaction imaging relies upon the source of monochromatic photons via a nuclear reaction between an ion accelerated to MeV-scale energy and a target. Gamma rays at discrete energies are produced from nuclear excited states of the product nucleus, with some reactions also producing neutrons. The collimated, penetrating radiation from the nuclear reaction source is used to perform transmission radiography of a shielded object, while neutron/gamma discriminating detectors detect the signature of nuclear fission. (b) Photon spectrum from the 11B(d,nγ)12C reaction measured with a LaBr scintillation detector. The detector is capable of measurement of the 15.1 MeV peak despite of small crystal size. It is also able to resolve the full energy peaks (labeled as “f”) and single (“s”) and double (“d”) escape peaks. Also shown are “j” and “k” peaks corresponding to other nuclear transitions in the target. (c) Energy-dependent attenuation for several elements (4.438 MeV and 15.1 MeV gamma energies from the 11B(d,nγ)12C reaction are shown as dashed lines).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Illustration of the imaging method using a low-energy nuclear reaction radiation source.(a) Low-energy nuclear reaction imaging relies upon the source of monochromatic photons via a nuclear reaction between an ion accelerated to MeV-scale energy and a target. Gamma rays at discrete energies are produced from nuclear excited states of the product nucleus, with some reactions also producing neutrons. The collimated, penetrating radiation from the nuclear reaction source is used to perform transmission radiography of a shielded object, while neutron/gamma discriminating detectors detect the signature of nuclear fission. (b) Photon spectrum from the 11B(d,nγ)12C reaction measured with a LaBr scintillation detector. The detector is capable of measurement of the 15.1 MeV peak despite of small crystal size. It is also able to resolve the full energy peaks (labeled as “f”) and single (“s”) and double (“d”) escape peaks. Also shown are “j” and “k” peaks corresponding to other nuclear transitions in the target. (c) Energy-dependent attenuation for several elements (4.438 MeV and 15.1 MeV gamma energies from the 11B(d,nγ)12C reaction are shown as dashed lines).
Mentions: One of the key characteristics of the low-energy nuclear reaction source is that the energies of the emitted gamma rays are governed by the nuclear structure rather than the detailed characteristics of the interaction region and interacting particles, as is the case with bremsstrahlung and inverse Compton scattering. The concept of the detection and imaging approach employed in this work is illustrated in Fig. 1a. The 11B(d,nγ)12C reaction is driven by a radio-frequency quadrupole accelerator, which produces a 3-MeV D+ beam with a typical current on the order of tens of μA. The D+ beam is incident onto a natural boron target placed inside the vacuum system of the accelerator. In addition to emission of an energetic neutron, this exothermic reaction efficiently populates the high-energy excited states of the product 12C nucleus, as has been shown in prior work15. The 12C nucleus subsequently emits gamma rays, with the most prominent yields at 4.438 MeV (2+ → 0+) and 15.1 MeV (1+ → 0+). Based on experimental measurements and independently characterized intrinsic efficiency of the detectors used, the gamma ray yields in our experiments were 5.3 × 107 s−1 μA−1 and 6.2 × 106 s−1 μA−1 at 4.438 MeV and 15.1 MeV, respectively; the fast neutron yield was 1.3 × 109 s−1 μA−1. The 12C nucleus can also be excited to produce gamma rays by another reaction, 12C(p,p’)12C, which does not produce neutrons, but relatively high energies (~18 MeV) of the incident protons are needed to exceed the reaction threshold. In our experiment with the 11B(d,nγ)12C target, the emitted radiation is collimated into a fan beam using concrete shielding; the produced neutrons can also be efficiently removed from the beam using borated polyethylene without significantly affecting the high-energy photon flux. The examined object can be placed a variety of distances from the source, with the closest practical distance of 100 cm in our experiment. The details of experimental setup including facilities, imaging objects, detector array positions, and operating characteristics can be found in Supplementary Materials.

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