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3 experiments

Current status on experimental investigations on prompt fission neutrons spectra T. Granier CEA DAM DIF, Bruyères le Châtel, Arpajon, France. 3 experiments. 239Pu PFNS (Los Alamos) 238U mean prompt neutron multiplicity measurement (Los Alamos) 238U and 235U PFNS (Bruyères le Châtel).

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3 experiments

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  1. Current status on experimental investigations on prompt fission neutrons spectraT. GranierCEA DAM DIF, Bruyères le Châtel, Arpajon, France T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011

  2. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 3 experiments • 239Pu PFNS (Los Alamos) • 238U mean prompt neutron multiplicity measurement (Los Alamos) • 238U and 235U PFNS (Bruyères le Châtel)

  3. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 239Pu PFNS • Experiment performed in the framework of the CEA/DAM-DOE-NNSA cooperation agreement on basic sciences • Collaborators: T. Granier, A. Chatillon, B. Laurent, J. Taieb, G. Bélier CEA DAM DIF, Bruyères le Châtel, France RC Haight, R.O Nelson, J. O’Donnell, M. Devlin, S. Noda LANL, Los Alamos, USA

  4. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 PFNS investigations at LANSCE/WNR 800 MeV protons • 800 MeV protons • Pulsed mode • Spallation in W targets • Unmoderated spallation neutrons (WNR) Lujan WNR

  5. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 PFNS investigation at LANSCE/WNR • Nuclear physicists from CEA initiated an experimental program in Los Alamos to study PFNS • FIGARO (Bob Haight) array of organic liquid scintillator (analogous to NE-213) n detectors • Multi-plate fission chambers loaded with hundreds mg of actinide • Double time of flight • n-γ discrimination based on pulse shape • Detection efficiency measured with 252Cf Figaro (WNR) Neutron detectors Collimated n beam TOF 2 / ~1 m TOF 1 / ~22 m Fission chamber Collimated pulsed n beam Multi-plate fission chamber designed in CEA

  6. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 Investigation of 239Pu at WNR • 1st experiment: Phys. Rev. C 83 3 034604 (2011), S. Noda et al. • Newer results on 239Pu from a second, improved experiment have need obtained (analysis by A. Chatillon) • Examples of PFNS obtained

  7. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 Investigation of 239Pu at WNR • Measured PFNS are systematically lower than models above 5 MeV • There seems to be independent indications that ENDF/B-VII PFNS are too hard

  8. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 238U(n,f) Nu-bar • Goal of the experiment: Fragment mass yields, Fragment kinetic energy, neutron multiplicity • Collaboration CEA/DAM-JRC/IRMM-LANL • Experiment performed at LANSCE/WNR • IRMM double Frisch-Gridded ion chamber with 1 mg 238 sample • CEA fission neutron counter • Collaborators: T. G., B. Laurent, G. Bélier, A. Chatillon, J. Taieb, H. Duarte CEA-DAM DIF, Bruyères le Châtel, France F.-J. Hambsch, S. Oberstedt, P. Salvador Castineira EC-JRC-IRMM, Geel, Belgium F. Tovesson, A. Laptev, R.C. Haight, R.O. Nelson, J. O’Donnell LANSCE-NS, Los Alamos National Laboratory, USA

  9. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 WNR N beam 3He det. Fission chamber Poly moderator Experiment principle • Conjunction of 2 detectors: • Double Frisch-gridded ion chamber: • Double kinetic energies E1, E2 of post neutron fragments • emission angle of both post neutron fragments • Neutron counter • Number of neutrons emitted in coincidence • Time of flight is used to measure incident neutron energy

  10. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 LANSCE-WNR 800 MeV protons • Spallation neutrons • “White” neutron source • 0.1 < En < 200 MeV • Pulsed mode: Time-of-flight

  11. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 LANCSE-WNR Pulsed beam 800 MeV protons (200ps) makes broad spectrum of neutrons by spallation reactions

  12. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 The double kinetic energy method • E1 and E2 (post neutron) measured • Conservation of mass and momentum • At low energy and for preneutron fragments: • A1/A2=E2/E1 • A+1=A1+A2 • Corrections • Energy loss of fragments in target-substrate • Pulse height defect • Neutrons emitted vs. A (constrained by coincident neutron measurement) • kinematics • Iterative procedure required→ A1,A2 pre and post neutron • Resolution on mass corresponds at best to a sigma of ~2 mass units

  13. 238U The IRMM double Frisch-gridded ion chamber • 238U sample, 1 mg, vacuum-evaporated onto thin polyimide film • Energy and angle are measured for both FF (summing method) • Precision pulse generator used for signal-drift monitoring • Counting gas: P-10 (90%Ar+10% CH4). • 1.05 bar gas pressure. • 0.1 l/min gas flow. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011

  14. The CEA fission neutron counter • 30 3He tubes in 2 rings surrounding fission chamber • 3He tubes are within a polyethylene block to moderate fission neutrons • Neutrons are counted and time-stamped during 150 μs after each trigger • Efficiency ~25% for 252Cf (in this configuration) • Assembly is shielded against room return using poly+boron carbide • Insensitive to gamma rays T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011

  15. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 In real life, at WNR Experimental setup on 90 L flight path

  16. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 Cosine of emission angle En=200 MeV Emitted neutron energy (MeV) Neutron efficiency correction • Counting efficiency vs neutron energy and emission angle studied by means of MC simulations using MCNPX • Efficiency measured with 252Cf (in perfect agreement with simulations) • For incident neutron energy below ~20 MeV, compatible with constant efficiency (excellent agreement with Fréhaut data) • Above ~20 MeV, the BRIEFF code is used: • angle x energy double differential neutron spectra calculated with BRIEFF code for different incident neutrons energies from 20 to 200 MeV used as neutron sources in MCNPX calculations

  17. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 238U Nu-bar measurement • 12 days beam • 1 mg 238U target Fréhaut et al., CEA Bruyères le Châtel 1980 Ethvignot et al., LANL-CEA 2002 This Work

  18. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 Preliminary fragment anisotropy data • Fission fragment anisotropy in center of mass

  19. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 Preliminary fragment mass distribution data • Preliminary mass distributions for 2 incident neutron energy groups

  20. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 TiT or TiD target Fission chamber p or d beam ~0.9 m flight path n shielding (Li paraffin) N-γshadow bar Lead shielding Paraterphenyl detector New PFNS measurements at CEA • Van de Graaff 4 MV HVEC • Quasi monoenergetic neutrons • 7Li(p,n) ~500 keV • T(p,n) : 1-3 MeV • D(d,n) : 3-7 MeV • T(d,n) : 15-20 MeV • Time of flight method • Paraterphenyl detector (Kharkov) • better sensitivity to low energy neutrons • Detection efficiency: 252Cf + MC simulations

  21. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 New PFNS measurements at CEA • Goal: PFNS precision measurements for a few incident neutron energies • Current experiments: 238U, 235U • Currently: flux limitations due to radiation protection issues • Should be solved soon • Implementation of new shielding • New operation mode will allow us to run the accelerator at high current • Planned measurements: 235U, 239Pu, 232Th …

  22. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 BRC eval. 2011 BRC LA model 238U(n,f) at 6.5 MeV, spectral shape • Preliminary result in agreement with previous measurements by Kornilov and Lovchikova: effect of the opening of 2nd chance fission • Major data libraries currently fail to describe this effect

  23. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 Perspectives • Experiments with higher neutron flux in Bruyères le Châtel • New shielding • Operation after hour with extended exclusion area • Experiments in Geel in collaboration with F-J Hambsch and S. Oberstedt • 1st test in mid 2012 : 235U at 0.5 MeV with fission chamber • Remark: PFNS precision measurement in the domain 7-8 MeV can lead to information on the probability ratio 1st chance/2nd chance

  24. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 This measurement Eval. by V. Maslov 235U(n,f) at 6.5 MeV PFNS shape • 235U(n,f), En=6.5 MeV, Spectral shape

  25. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 A few words on the current PFNS evaluation in Bruyères • As outlined by V. Maslov in last meeting : LA model fails at describing the 2nd chance PFNS • B. Morillon and P. Romain now include the prefission spectrum calculated within the cross section evaluation using the Talys code (Hauser-Feschbach + Exciton model)

  26. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 • Additional material

  27. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 σ (barns) 2 4 6 8 10 12 14 16 18 Neutron energy (MeV) Prompt fission neutrons • Deexcitation of the fragments in flight • When En > Bf, opening of 2nd chance fission (emissive fission, pre-fission neutrons) • Neutron emission at scission (scission neutrons) probably exist n A+1 A n A A A+1

  28. T. Granier , CEA-DAM – IAEA ‘s CRP on PFNS, 2nd meeting, Vienna, 13-16 December 2011 Examples of preliminary results 238U(n,f), En=6.5 MeV, spectral shape • Preliminary result confirms previous measurements by Kornilov and Lovchikova: effect of the opening of 2nd chance fission • Major data libraries fail to describe this effect

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