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

2. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 2 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, 2 nd meeting, Vienna, 13-16 December 2011 3 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, 2 nd meeting, Vienna, 13-16 December 2011 4 PFNS investigations at LANSCE/WNR 800 MeV protons Pulsed mode Spallation in W targets Unmoderated spallation neutrons (WNR) 800 MeV protons WNR Lujan

5. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 5 PFNS investigation at LANSCE/WNR Collimated n beam Figaro (WNR) Multi-plate fission chamber designed in CEA 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 TOF 2 / ~1 m Neutron detectors Fission chamber TOF 1 / ~22 m Collimated pulsed n beam

6. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 6 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, 2 nd meeting, Vienna, 13-16 December 2011 7 Measured PFNS are systematically lower than models above 5 MeV There seems to be independent indications that ENDF/B-VII PFNS are too hard Investigation of 239Pu at WNR

8. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 8 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, 2 nd meeting, Vienna, 13-16 December 2011 9 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 3He det. Fission chamber Poly moderator WNR N beam

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

11. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 11 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, 2 nd meeting, Vienna, 13-16 December 2011 12 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. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 13 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. 238 U

14. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd 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

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

16. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 16 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 Emitted neutron energy (MeV) Cosine of emission angle En=200 MeV

17. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 17 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, 2 nd meeting, Vienna, 13-16 December 2011 18 Preliminary fragment anisotropy data Fission fragment anisotropy in center of mass

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

20. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 20 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 Paraterphenyl detector n shielding (Li paraffin) Fission chamber TiT or TiD target ~0.9 m flight path N- γ shadow bar p or d beam Lead shielding

21. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 21 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, 2 nd meeting, Vienna, 13-16 December 2011 22 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 2 nd chance fission Major data libraries currently fail to describe this effect BRC eval. 2011 BRC LA model

23. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 23 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/2 nd chance

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

25. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 25 A few words on the current PFNS evaluation in Bruyères As outlined by V. Maslov in last meeting : LA model fails at describing the 2 nd 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, 2 nd meeting, Vienna, 13-16 December 2011 26 Additional material

27. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 27 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 A+1 n A A     

28. T. Granier, CEA-DAM – IAEA ‘s CRP on PFNS, 2 nd meeting, Vienna, 13-16 December 2011 28 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 2 nd chance fission Major data libraries fail to describe this effect