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In-field identification of neutron sources

In-field identification of neutron sources. C.T. Nguyen, J. Bagi, L. Lakosi, J. Huszti K. Szirmai, Z. Hlavathy, I. Almasi, J. Zsigrai zsigrai@mail.kfki.hu. Contents. Categories of neutron sources Options for neutron-source identification

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In-field identification of neutron sources

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  1. In-field identification of neutron sources C.T. Nguyen, J. Bagi, L. Lakosi, J. Huszti K. Szirmai, Z. Hlavathy, I. Almasi, J. Zsigrai zsigrai@mail.kfki.hu In-field identification of neutron-sources

  2. Contents • Categories of neutron sources • Options for neutron-source identification • Application of neutron-coincidence counting for identification of neutron sources • “Traditional” application of NCC vs. neutron source identification • Possible practical realizations • Problems at high count rate and solution • NCC at the Institute of Isotopes

  3. What is a neutron source? • Radioactive material emitting neutrons • Neutrons from • Spontaneous fission • Induced fission • (a,n) reactions • … For example: TIME CORRELATED SPONTANEOUS-FISSION NEUTRONS : D1 Pu n RANDOM NEUTRONS: S PuBe13 Be(,n) Be(n,2n) Pu(n,f) n n 9Be In this presentation we do not consider other sources of neutrons (e.g. nuclear reactors, neutron generators etc.) TIME CORRELATED INDUCED-FISSION AND Be(n,2n) NEUTRONS:D2

  4. Categories of neutron sources – according to neutron emission S: Random neutrons D1: spontaneous fission neutrons D2: induced fission neutrons D=D1+D2 • Dominantly fission sources • D1>>D2, DS • Pu metal • Pu-oxide • MOX • Cf-252: • Cm-244 • Mixed • D1  D2, D<S • PuF4 • (a,n) sources • D1 << D2, D<<S • PuBe • Am-Be • Am-Li For example: TIME CORRELATED SPONTANEOUS-FISSION NEUTRONS : D1 Pu n RANDOM NEUTRONS: S PuBe13 Be(,n) Be(n,2n) Pu(n,f) n n 9Be TIME CORRELATED INDUCED-FISSION AND Be(n,2n) NEUTRONS:D2

  5. Categories of neutron sources – according to threat • Pu in various forms • Pu metal, • Pu-oxide, • MOX, • PuF4, • Pu-Be sources • ….. • Everything else • Spontaneous-fission sources • Cf-252 • Cm-244 • … • (α,n) sources • Am-Be • Am-Li • … Proliferation hazard

  6. How to identify and characterize neutron sources? Gamma spectrometry Gammas Neutronsource Neutrons Heat Neutron counting Calorimetry

  7. How to identify and characterize neutron sources? Gamma spectrometry + Standalone technique +++ Can be used anywhere - Shielding may cause problems Gammas Neutronsource Neutrons Heat Neutron counting +Satisfactory accuracy ++Shielding no problem +Standalone technique +++Can be used anywhere Calorimetry +++Very good accuracy -Not a standalone method ---Can be used only in the lab -Shielding may cause problems

  8. What can a first responder do? • Commonly used equipment: • Personal Radiation Devices: gamma and neutron rate display • Radiation Identifiers: low-resolution gamma spectrometry (mainly NaI) • Background:No scientific background • Knowledge:Basic training (1-2 weeks) • Capability:To handle simple cases

  9. And the expert team? Commonly used equipment: Portable HPGe: High-resolution gamma spectrometry Background:Scientific Capability: Case assessment Making decisions Implementing specific approaches

  10. Gamma spectrometry Unshielded sources Shielded or masked sources Shielded source spectrum Neutron source type Isotopic composition Fissile content ?

  11. Gamma spectrometry • Detecting the presence of Be Commercial applications stop here

  12. Neutron measurements • Gross neutron detection: • Equipment needed: personal radiation detector • Neutron count rate Rough idea about neutron yield • Neutron coincidence counting: • Equipment needed: neutron detector (3He) + electronics + software (!) Gross count rate, S Coincidence rate, D And their ratio, D/S Estimated neutron yield Number of spontaneous fissions and secondary reactions Neutron source type, Neutron yield, Fissile content, Estimated isot. comp. of Pu Heavy–metal shielding is no problem for neutrons!

  13. “Traditional” application of NCC vs. identification of neutron sources “Traditional” application : • Determination of 240Pueffective mass, based on detection of time correlated neutrons (Dspontaneous)from spontaneous fission of Pu isotopes Identification of N-sources: • Detection of both spontaneous and induced fission neutrons • For (a,n) sources S>>Dinduced>>Dspontaneous • D/S: number of fissions induced by a one random neutron m240effective = 238m238 + m240 + 242m242 SPONTANEOUS-FISSION NEUTRONS : D1 Pu n RANDOM NEUTRONS: S PuBe n n Be INDUCED-FISSION AND Be(n,2n) NEUTRONS:D2

  14. D/S S Identification of neutron sources by neutron coincidence counting Ratio of coincidences (“doubles”) to total counts (“singles”) as a function of total count rate • Different sources on different curves • Curve determined by: • Specific neutron yield • Isotopic composition

  15. D/S S Identification of neutron sources by neutron coincidence counting Ratio of coincidences (“doubles”) to total counts (“singles”) as a function of total count rate • Dominantly fission sources • D1>>D2, DS • Pu metal • Pu-oxide • MOX • Cf-252: • Cm-244 • Mixed • D1  D2, D<S • PuF4 • (a,n) sources • D1 << D2, D<<S • PuBe • Am-Be • Am-Li S: Random neutrons, D1: spontaneous fission neutrons D2: induced fission and Be(n,2n) neutrons, D=D1+D2

  16. D/S S Identification of neutron sources by neutron coincidence counting Ratio of coincidences (“doubles”) to total counts (“singles”) as a function of total count rate • Plutonium • E.g. pure Pu,Pu-Be with various isotopic composition • Everything else • Spontaneous-fission sources • (α,n) sources

  17. D/S S Identification of neutron sources by neutron coincidence counting • Neutron source type • Presence of Pu • Isotopic composition of Pu • Mass of fissile isotope • Pu isotopic composition can be estimated also for high-burn-up Pu (with 239Pu < 70%), for which MGA fails!

  18. Specific neutron yield • Important parameter for determining the origin of the source Neutron yield Mass Specific neutron yield Further characterization of (a,n) sources • Total Pu content of Pu-Be sources MPu~D/S S>>Dinduced>>Dspontaneous • Analogously for other (a,n) sources

  19. Possible realizations Canberra HLNC IKI prototype Ortec fission meter Detector Electronics JSR-15 AMSR 150 PTR-II List mode operation Pulse train analysis Die-away time calculation Software Shift (multiplicity) register Detector calibration Using neutron sources at IKI

  20. Possible upgrades of the IKI prototype • Modules in Closed and open geometry • Real-time Monte-Carlo simulations for calibrating actual source-detector configuration

  21. Problems at high count rates • Many neutron sources have neutron output >106 n/s • Dead-time losses strongly influence accurate measurement of D • JCC-13 (18 det./3 amp.) +JSR14 can not operate correctly with sources emitting > ~106 n/s • HLNC (JCC-31:18 det./6 amp.) +JSR14 can not operate correctly with sources emitting > 107 n/s

  22. Problems at high count rates Similar efforts at IAEA: • Activities Supported Through Regular Budget in the IAEA R & D Programme for Nuclear Verification 2010–2011 • NDA Activity #7: Analysis and considerations of potential gaps in the point model aiming at finding the methodological error sources in highly intensive neutron counting • NDA Activity #8: Analysis and consideration of possibilities to minimize and account correctly for dead time in the method of neutron coincidence counting using 3He in moderator • Possible solution: Separate amplifiersand separate data acquisition channelsfor each 3He tube (see next presentation)

  23. Complex approach for characterization Neutron source type, Neutron yield, Amount, Precise isotopic comp. of Pu Neutron source type, Neutron yield, Amount, Estimated isotopic comp. of Pu Neutron source type, Amount, Precise isotopic comp. of Pu

  24. NCC at the Institute of Isotopes • A set of well characterized neutron sources is available at IKI: 1 AmLi, 3 AmBe, 7 Pu-Be, 2 242Cm, 5 252Cf (characterization by HRGS, calorimetry, NCC, neutron-radiography) • Field test of IKI prototype performed, in attendance of IAEA and JRC observers • Pu content of ~80 Pu-Be sources measured and safeguards accountancy corrected: total of 563±15 g of Pu, instead of 2050 g ! • Development of nuclear electronics for list-mode data acquisition Pu-Be neutron sources repackaged into new containers Home-made neutron counter

  25. Conclusion • NCC can be successfully applied for identification of neutron sources • Pu in any form (pure Pu, Pu-Be …) can be separated from pure fission and (a,n) sources • Appropriate hardware and software needed • Coincidence counter, List mode electronics, Multichanel data collection dealing with high count rates • Prototype readily available • Help in testing and validation and suggestions for improvement arewelcome!

  26. Thank you for your attention! www.iki.kfki.hu zsigrai@mail.kfki.hu

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