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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.


Observation of emission of beta delayed neutrons as a unique signature of material undergoing nuclear fission.The interrogating beam is turned off at time = 0 s. (a) Temporal profile of delayed neutrons with a natural uranium target observed using a low-threshold composite fast neutron detector is in good agreement with a common parameterization into six delayed neutron groups (red line). (b) Temporal profile of delayed neutrons with a tungsten target using a low-threshold composite fast neutron detector shows no emission of delayed neutrons. More information on the neutron measurements is provided in Supplementary Materials.
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f4: Observation of emission of beta delayed neutrons as a unique signature of material undergoing nuclear fission.The interrogating beam is turned off at time = 0 s. (a) Temporal profile of delayed neutrons with a natural uranium target observed using a low-threshold composite fast neutron detector is in good agreement with a common parameterization into six delayed neutron groups (red line). (b) Temporal profile of delayed neutrons with a tungsten target using a low-threshold composite fast neutron detector shows no emission of delayed neutrons. More information on the neutron measurements is provided in Supplementary Materials.

Mentions: Independent measurement of material areal density and Zeff may not be sufficient to detect the presence of elements and specific isotopes that could be used as nuclear explosives (233U, 235U, and 239Pu), as illustrated in Fig. 3c. A unique signature of fissionable materials is the emission of characteristic prompt and delayed radiation (neutrons and gamma rays). Both the neutrons and the 15.1 MeV gamma ray produced in the 11B(d,nγ)12C reaction are suitable for inducing nuclear fission. Prompt radiation produced in fission is challenging to detect due to the high intensity of background; in the case of the 11B(d,nγ)12C reaction this includes the gamma rays and neutrons emitted by the source itself and photoneutrons produced in the surrounding materials, especially higher Z materials. This motivates the detection of delayed neutrons and gamma rays, which also exhibit a characteristic decay profile. To augment the imaging, we performed an experiment using natural uranium (99.3% 238U, 0.7% 235U) irradiated by the nuclear reaction source, in which fission was induced predominantly by neutrons. The delayed neutron emission is coincident with the abundant emission of photons originating from activation of surrounding material and from fission products, if fission is induced. Separation of beta-delayed neutrons, which have relatively low energy (mean energy of ~0.5 MeV prior to any thermalization in the surrounding medium), from the photon background can be challenging. We realized this separation at a low energy threshold by a novel class of neutron detector based on a composite of Li-doped glass and scintillating plastic, which relies on capture gating together with pulse height and pulse shape discrimination21. In Fig. 4a,b, we present the detected delayed neutron signature from natural uranium and tungsten, respectively, demonstrating the capability of the 11B(d,nγ)12C reaction to simultaneously provide a suitable probe for discovery of special nuclear material, if the beta-delayed radiation can escape the material shielding. We note that the emitted neutrons and 15.1 MeV photons, along with the photoneutrons produced in the object and the object’s surroundings, can temporarily activate the materials, enabling another mode for achieving elemental and isotopic specificity via the well-developed techniques of neutron activation analysis22 and photon activation analysis23.


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

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

Observation of emission of beta delayed neutrons as a unique signature of material undergoing nuclear fission.The interrogating beam is turned off at time = 0 s. (a) Temporal profile of delayed neutrons with a natural uranium target observed using a low-threshold composite fast neutron detector is in good agreement with a common parameterization into six delayed neutron groups (red line). (b) Temporal profile of delayed neutrons with a tungsten target using a low-threshold composite fast neutron detector shows no emission of delayed neutrons. More information on the neutron measurements is provided in Supplementary Materials.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Observation of emission of beta delayed neutrons as a unique signature of material undergoing nuclear fission.The interrogating beam is turned off at time = 0 s. (a) Temporal profile of delayed neutrons with a natural uranium target observed using a low-threshold composite fast neutron detector is in good agreement with a common parameterization into six delayed neutron groups (red line). (b) Temporal profile of delayed neutrons with a tungsten target using a low-threshold composite fast neutron detector shows no emission of delayed neutrons. More information on the neutron measurements is provided in Supplementary Materials.
Mentions: Independent measurement of material areal density and Zeff may not be sufficient to detect the presence of elements and specific isotopes that could be used as nuclear explosives (233U, 235U, and 239Pu), as illustrated in Fig. 3c. A unique signature of fissionable materials is the emission of characteristic prompt and delayed radiation (neutrons and gamma rays). Both the neutrons and the 15.1 MeV gamma ray produced in the 11B(d,nγ)12C reaction are suitable for inducing nuclear fission. Prompt radiation produced in fission is challenging to detect due to the high intensity of background; in the case of the 11B(d,nγ)12C reaction this includes the gamma rays and neutrons emitted by the source itself and photoneutrons produced in the surrounding materials, especially higher Z materials. This motivates the detection of delayed neutrons and gamma rays, which also exhibit a characteristic decay profile. To augment the imaging, we performed an experiment using natural uranium (99.3% 238U, 0.7% 235U) irradiated by the nuclear reaction source, in which fission was induced predominantly by neutrons. The delayed neutron emission is coincident with the abundant emission of photons originating from activation of surrounding material and from fission products, if fission is induced. Separation of beta-delayed neutrons, which have relatively low energy (mean energy of ~0.5 MeV prior to any thermalization in the surrounding medium), from the photon background can be challenging. We realized this separation at a low energy threshold by a novel class of neutron detector based on a composite of Li-doped glass and scintillating plastic, which relies on capture gating together with pulse height and pulse shape discrimination21. In Fig. 4a,b, we present the detected delayed neutron signature from natural uranium and tungsten, respectively, demonstrating the capability of the 11B(d,nγ)12C reaction to simultaneously provide a suitable probe for discovery of special nuclear material, if the beta-delayed radiation can escape the material shielding. We note that the emitted neutrons and 15.1 MeV photons, along with the photoneutrons produced in the object and the object’s surroundings, can temporarily activate the materials, enabling another mode for achieving elemental and isotopic specificity via the well-developed techniques of neutron activation analysis22 and photon activation analysis23.

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.