Detecting well-shielded nuclear material in cargo containers via active neutron interrogationEric B. NormanLawrence Livermore National LaboratoryEric B. NormanLawrence Livermore National LaboratoryPotential danger at the world’s sea ports The Port of OaklandSan Francisco Bay, CaliforniaOakland Bay BridgeSan Francisco~ 2 mi• 90% of the world’s trade moves via sea-going containers• Cargo is attractive for smuggling illicit material-Large volume and mass of material in each container- Cargo is non-homogeneous• Volume of traffic is enormous-More than 6,000,000 containers enter the U.S. annually- U.S. west coast ports are processing 11,000/day— An average of 8/min on a 24/7 basis•Successful delivery of one weapon of mass destruction in a container can be catastrophic87.06,241,000Top 10 total48.52,764,500Top 10 total3.3233,000Houston2.0114.000Yantian3.7268,000Oakland2.1119,700Genoa3.8273,000Tacoma2.8159,600Tokyo4.0284,000Seattle4.5256,500Bremerhaven4.3306,000Norfolk5.0285,000Puson4.3312,000Savannah5.1290,700Rotterdam5.2376,000Charleston5.6319,200Kaohsiung14.61,044,000NY / New Jersey5.8330,600Singapore19.11,371,000Long Beach5.8330,600Shanghai24.71,774,000Los Angeles9.8558,600Hong Kong% of total trafficU.S. arrivalsPort of entry% of total trafficOutbound to U.S. Port of originTop 10 domestic ports of entryTop 10 foreign ports of origin29%6%18%5%8%13%6%15%Foodstuffs & TreeProductsFurniture & PrefabConstruction MatlRefined Metals & MineralManufacturesHeavy MachineryUnspecified ManufacturedArticlesLight Machinery (Office,Medical & Scientific)VehiclesOtherThe cargo is the challenge20 ft / 40 ftCargo container8.5 ft8.5 ft• Cargo material is diverse• Containers are very large• Packing is inhomogeneous• Need a reliable scan•tscan< 1 min / container• Concentrate on the threat with the gravest consequences—nuclear explosives– Uranium and plutonium with very high isotopic content of the nuclides 235U and 239Pu– Heavily shielded material• Develop a prototype detection system for use at sea ports– Functions for a range of material density: 0 < ρL < 150 g/cm2– Is reliable: False positive and false negative rates < 10-3– Preserves the flow of commerce through the port: tscan< 1 min / containerScope of the projectWe need a useful signature unique to fissionable material• Radiation must penetrate from deep within a cargo container to reach a detector outside and must be intense enough to be discriminated from background•235U and 239Pu are both radioactive and have unique gamma radiation signatures. Can we exploit these passive emissions?–239Pu (t1/2= 2.4x104yr) emits weak gamma rays and neutrons–235U (t1/2= 7.0 x108yr) emits weak, low-energy gamma rays • Active methods inject particles into container to produce fission reactions in fissile material and provide unique return signals• We don’t expect to rely exclusively on active approaches– Passive radiation detection– Radiography to locate high-density components buried within an otherwise low-density cargoActive interrogation“Prompt”235U(n,γ)236UDetect capture γ-raysProblem: mass(U or Pu) < 10 kgmass (other cargo) = 10,000 kgS/N is very smalland need high energy resolution detectors to identify U or Pu• Thermal-neutron induced fission reaction produces two fission fragments and zero to many neutrons. For example:n + 235U !236U* !90Kr + 143Ba + 3nβ-decay of the fission fragments frequently leaves thedaughter nucleus in an excited state– Sometimes above the binding energy of the last neutron => neutron emission– More often to a high-energy state that de-excites by high-energy γ-ray emission−γ-ray emission is 10 times more likely– Both processes are fission signaturesA word about the fission reaction andβ-delayed gamma rays and neutronsDelayed n or γ?0.030.0170.046γ-rays at Eγ> 4 MeV [2]0.110.0650.127γ-rays at Eγ> 3 MeV [2]0.0440.00610.015Delayed neutrons [1]238U fast fission239Pu thermal fission235U thermal fissionYield /fission[1] LLNL Nuclear Data Group, 2003, http://nuclear.llnl.gov/CNP/nads/[2] LBNL Isotope Explorer, 2003, http://ie.lbl.gov/ensdf/The high energy γ-ray signal leaving thick hydrogenous cargo may be as much as 102to 104larger than the delayed-n flux.Delayed γ-ray yields are approx. one order of magnitude higher than delayed neutron yieldsYield / FissionAttenuation [3]Thickness of Al or wood (g/cm2)FluxDelayed neutrons are highly attenuated in hydrogenous material (estimate includes yield / fission) 1.E-061.E-051.E-041.E-031.E-021.E-011.E+000 50 100 150 2003 MeV gammas in Al300 keV neutrons in Al3 MeV gammas in wood300 keV neutrons in wood[3] T. Rockwell III, Reactor Shielding Design Manual, D. Van Nostrand Co., New York (1956).Can we use this signature to distinguish between 235U and 239Pu?• Gamma-ray yield ratios• Decay curvesNeutron-induced fission-fragment mass distributions [1][1] www.kayelaby.npl.co.uk, T.R. England and B.F. Rider, (1992) OECD Report, NEA/NSC/DOC(92) p. 346High-energy gamma-ray yields in 235U thermal neutron fissionNuclide Half-life (sec) > 4 MeV gammasper fission> 3 MeV gammasper fission85Se 39. 0.0 0.001286Br 55. 0.0013 0.001387Br 55. 0.0045 0.007388Br 16. 0.0045 0.007289Br 4.4 0.0016 0.002189Kr 189. 0.00064 0.002990-mRb 258. 0.00063 0.003690Rb 156. 0.0089 0.01691Kr 8.6 0.000047 0.002091Rb 58. 0.0052 0.01792Rb 4.5 0.011 0.01293Rb 5.9 0.00078 0.007394Rb 2.7 0.00022 0.001595Rb 0.38 0.000027 0.001195Sr 25. 0.00052 0.003197Y 3.8 0.0 0.01798-mY 0.59 0.003 0.007136Te 17.5 0.0 0.0020136I 83. 0.0005 0.0011138I 6.5 0.00043 0.0010140Cs 63. 0.0 0.0038141Cs 25. 0.0 0.0017142Cs 1.8 0.00054 0.0014Total, includingactivities not shownVarying 0.0458 0.127High-energy gamma-ray yields in 239Pu thermal fissionNuclide Half-life(sec)87Br 55. 0.0015 0.002588Br 16. 0.0013 0.002090-mRb 258. 0.00038 0.002190Rb 156. 0.0025 0.004691Rb 58. 0.0020 0.006392Rb 4.5 0.0045 0.004993Rb 5.9 0.00031 0.002995Sr 25. 0.0003 0.001797Y 3.8 0.0 0.01398Y 0.59 0.0024 0.0055106Tc 36. 0.0 0.0066140Cs 64. 0.0 0.0026141Cs 25. 0.0 0.0014142Cs 1.8 0.00037 0.0022Total includingactivities not shown Varying 0.017 0.065>4 MeVgammas/fission>3 MeVgammas/fissionHigh-energy γ-rays detected between neutron pulses are used to identify fissile material• Fission product γ-rays integrated from 3 to 7 MeV between interrogation beam pulses are used to identify the presence of fissionable material– Distinguished from
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