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O. Serot, O. Litaize, D. Regnier CEA-Cadarache, DEN/DER/SPRC/LEPh,

CRP Prompt Fission Neutron Spectra of Actinides. O. Serot, O. Litaize, D. Regnier CEA-Cadarache, DEN/DER/SPRC/LEPh, F-13108 Saint Paul lez Durance, France. Plan. Introduction Calculation procedure Results on 252 Cf( sf ) Results on 235 U( n th ,f )

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O. Serot, O. Litaize, D. Regnier CEA-Cadarache, DEN/DER/SPRC/LEPh,

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  1. CRP Prompt Fission Neutron Spectra of Actinides O. Serot, O. Litaize, D. Regnier CEA-Cadarache, DEN/DER/SPRC/LEPh, F-13108 Saint Paul lez Durance, France 2nd ERINDA Progress MeetingCEA | 10 AVRIL 2012

  2. Plan • Introduction • Calculationprocedure • Results on 252Cf(sf) • Results on 235U(nth,f) • Results on 239Pu(nth,f) • Conclusion and outlook

  3. Calculation procedure • Calculation procedure • For each Fission Fragment: • Determination of A, Z, KE • Determination of J, pi • Desexcitation of the Fission fragments

  4. Calculation procedure AL , ZL , KEL Sampling of the light fragment: 1 Y(A,KE,Z)=Y(A) × Y(<KE>, sKE) × Y(Z) Nuclear charge distribution • Charge dispersion: • Most probable charge ZP taken from Walh evaluation and/or from systematic Pre Neutron Mass distribution Pre Neutron Kinetic Energy distribution

  5. Calculation procedure The mass and charge of the heavy fragment can be deduced: AH=240-AL ZH=94-ZL Its kinetic energy (KEH) is deduced from momentum conservation laws 2 AH , ZH , KEH Sampling of the spin parity of the light and heavy fragment: 3 (Jp)L (Jp)H sL: spin cut-off of the Light fragment sH: spin cut-off of the Heavy fragment

  6. Calculation procedure Partitioning of the excitation energy between the two fragments 4 The Total Excitation Energy (TXE) available at scission can be deduced: Total Kinetic Energy (From Audi-Wapstra) Total Excitation Energy Main assumptions At scission • The main part of the deformation at scission is assumed to be converted into intrinsic excitation energy during the FF acceleration phase (Ohsawa, INDS 251(1991)) After full acceleration of the FF

  7. Calculation procedure Exemple on 252Cf(sf) RTmax • The FF are considered as a Fermi gas, the intrinsic excitation energy is therefore written as: • This intrinsic excitation energy will be used for the prompt neutron and gamma emissions RTmin 78/174 126/126 120/132 7

  8. Calculation procedure • Level density parameter calculated from Ignatyuk’s model: Asymptotic level density parameter Effective excitation energy Shell corrections (Myers-Swiatecki, …) • Rotational Energy: ERot b: quadrupoledeformationtakenfrom Myers-Swiatecki We have taken: with k=0.6

  9. Calculation procedure Desexcitation of each fission fragment: A, Z, J, pi, E*, Erot 5 5a Weisskopf Model (uncoupled) • EL,H*=aTL,H • Neutron evaporation spectrum: • Neutron emission down to • Sn(J) = Sn + Erot(J) • Then Gamma emission simulated via level density + strength functions

  10. Calculation procedure Desexcitation of each fission fragment: A, Z, J, pi, E*, Erot 5 Hauser Feshbach formalism (coupled): 5b • E*L,H=aTL,H +Erot L,H • Take into account the conservation laws for the energy, spin and parity of the initial and final states • The emission probabilities of prompt neutron and prompt gamma are given by: FromPhDthesis D. Regnier • Level density used: Composite Gilbert Cameron Model • Tn: from optical model potential of Koning Delaroche (Talys Code) • Tg: obtained from the strength function formalism (Enhanced Generalized LOrentzian) • The competition between neutron and gamma can be accounted for

  11. Calculation procedure 5 free parameters for fission: sL, sH, RTmin, RTmax, Krigid Weisskopf Model (uncoupled) Hauser Feshbach formalism (coupled): • Level density model: • CGCM, CTM, HFB • Neutron tramsmission coefficient: from optical model (Koning-Delaroche, Jeukenne-Lejeune-Mahaut) • Gamma transmission: based on strength function (EGLO : Enhanced Generalized Lorentzian; SLO : Standard Lorentzian; HFB

  12. Results / 252Cf(sf) • Some Results on 252Cf(sf) • Comparison : Weisskopf / Hauser-Feshbach • With the Hauser-Fescbach model: • Impact of the level density • Impact of the optical model used for the Tn calculation Input data (pre-neutron mass and kinetic energy) from Varapai

  13. Results / 252Cf(sf) • Comparison : Weisskopf / Hauser-Feshbach Hauser-Fescbach model (coupled) sL=9.5 sH=9.0 RTmin=0.3 RTmax=1.5 krigid=0.75 (Varapai_coupled_V3) Weisskopf model (uncoupled) sL=8.5 sH=10.2 RTmin=0.7 RTmax=1.4 krigid=0.6 (Varapai_uncoupled_V2)

  14. Results / 252Cf(sf) • Coupled Hauser-Fescbach : • Impact of the level density model used From David Regnier Thesis • Coupled Hauser-Fescbach : • Impact of the optical model used for the Tn calculation From David Regnier Thesis

  15. Results / 252Cf(sf) Coupled Hauser Feshbach model From David Regnier Thesis • Impact of the optical model used for the Tn calculation on PFNS Impact of the level density model on PFNS

  16. Results / 235U(nth,f) Calculation performed for the 235U(nth,f) Hauser-Fescbach model (coupled) sL=7.2 sH=8.4 RTmin=0.9 RTmax=1.3 krigid=0.9 Input data (pre-neutron mass and kinetic energy) from Hambsch

  17. Results / 235U(nth,f) Probability of neutron emission

  18. Results / 235U(nth,f) Average neutron multiplicity as a function of TKE Slope_Nishio=18.5 MeV/n Slope=10.24 MeV/n

  19. Results / 235U(nth,f) Average neutron multiplicity as a function of pre-neutron mass

  20. Results / 235U(nth,f) Prompt Fission Neutron Spectrum

  21. Results / 239Pu(nth,f) Calculation performed for the 239Pu(nth,f) Presented at Workshop GAMMA2, Oct. 2013 • Standard I • Standard II • Super Long • RT Laws for each mode • Test the influence of the fission modes on the prompt neutron and gammacharacteristics: case of the thermal neutron induced fission of 239Pu • Describe for each fission mode the n and gcharacteristics

  22. Results / 239Pu(nth,f) Main characteristics of the fission modes Data taken from Dematté: PhD thesis, University of Gent, 1997 (Standard III fission mode is neglected) Very similar data were obtained by Schilleebeckx) 22

  23. Results / 239Pu(nth,f) Average Total Kinetic Energy Width of the Total Kinetic Energy 23

  24. Results / 239Pu(nth,f) Standard I Standard II Super Long Total 24

  25. Results / 239Pu(nth,f) Temperature Ratio Law: RT = TL/TH Standard I Standard II Super Long 108 / 132 120 / 120 102 / 138 Standard I is governed by the spherical neutron shell (N=82) + spherical proton shell (Z=50) Standard II is governed by the deformed neutron shell (N=88) + spherical proton shell (Z=50) Super Long is a strongly deformed mode

  26. Results / 239Pu(nth,f) Prompt Neutron Multiplicity FIFRELIN Results Experimental and evaluated data

  27. Results / 239Pu(nth,f) Prompt Neutron Multiplicity • Reasonable agreement between FIFRELIN calculation and the experimental data can be obtained • Best agreement is achieved with data from Batenkov (2004) • In the [115-120] mass region, the observed high experimental multiplicity could be reproduced by increasing the contribution of the Super Long fission mode • In the very asymmetric mass region, the St. III fission mode seen by Schillebeeckx could be interesting to add

  28. Results / 239Pu(nth,f) Prompt Neutron Multiplicity Different slopes obtained for each fission modes Different slopes obtained for Light and Heavy fragment

  29. Results / 239Pu(nth,f) Prompt Fission Neutron Spectrum • Rather similar average energy for both St. I and St. II modes • But, differences can be observed in the low and high energy part of the spectrum

  30. Results / 239Pu(nth,f) Prompt Neutron Spectrum: Ratio to Maxwellian with T=1.32

  31. Results / 239Pu(nth,f) Prompt Neutron Spectrum: Ratio to Maxwellian with T=1.32 Comparison with / without Fission modes

  32. Results / 239Pu(nth,f) Prompt Gamma Multiplicity FIFRELIN with De=[0 – infinity]

  33. Results / 239Pu(nth,f) Prompt Gamma Spectrum FIFRELIN with De=[0 – infinity] • Structures at low energy are visible for both St. I and St. II modes • Fails to reproduce the high energy part (above 5 MeV)

  34. Results / 239Pu(nth,f) Experimental Compilation from David Regnier FIFRELIN Calculation Excellent agreement with Verbinski’s data

  35. Results / 239Pu(nth,f) Average fragment remaining energy due to metastable StI Light FF = 0.04626 Heavy FF= 0.5323 StII Light FF = 0.1808 Heavy FF= 0.2812 SL Light FF = 0.08083 Heavy FF= 0.3699

  36. Conclusion • Many new developments have been done in the Monte Carlo code FIFRELIN • (in the frame of David REGNIER’s thesis) • The prompts neutron and gamma spectra obtained are in reasonable with experiments for: 252Cf(sf), 235U(nth,f) and 239Pu(nth,f) • The Hauser-Feshbach formalism used for the desexcitation of the fission fragments is the better model to get both prompt neutron and gamma spectra • It is recommended to use the • CGCM for the level density • the KD optical model for the Tn calculation • the EGLO for the strength function • It seems promising to use as input data (pre neutron mass and kinetic energy) the one deduced from the fission mode analysis

  37. Annexe

  38. Hauser-Fescbach model (coupled) sL=9.5 sH=9.0 RTmin=0.3 RTmax=1.5 krigid=0.75 (Varapai_V3) Hauser-Fescbach model (coupled) sL=8.5 sH=10.2 RTmin=0.7 RTmax=1.4 krigid=0.6 (Varapai_V1)

  39. Experimental data base on prompt gamma rays

  40. Influence: Spin cut-off on P(nu) Model Weisskopf 238U(n,f) (Same trend observed with HF coupled) From O. Litaize et al., ND2013

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