1 IAEA / CRP Prompt Neutron / 13-16th Dec Olivier SEROT 1, Olivier LITAIZE 1, Cristian MANAILESCU 1, 2, David REGNIER 1 1 CEA Cadarache, Physics Studies Laboratory F Saint Paul Lez Durance France 2 University of Bucarest, Faculty of Physics, Bucharest-Magurele, Romania Investigation of the prompt neutron characteristics from a Monte Carlo simulation of the fission fragment de- excitation

2 IAEA / CRP Prompt Neutron / 13-16th Dec Introduction Initial input data needed Calculation procedure Results on 252 Cf(sf) Results on 239 Pu(n,f) and 240 Pu(sf) Conclusion and outlook Plan

3 IAEA / CRP Prompt Neutron / 13-16th Dec Context Prompt neutron and prompt gamma spectra and their multiplicities are very important data for nuclear applications The evaluation files (JEFF,…) are not satisfactory: Lack of data, Same data for various fissioning nuclei, Dependence with the incident neutron not always taken into account Prompt gamma spectra not enough accurate and strongly needed by nuclear energy …) Our aim Development of a Monte Carlo code able to simulate statistical decay of the fission fragments: Various physical quantities can be investigated: (A,TKE), P( ), E  (A), N( ,A)…. Test models related to the emission process Introduction

4 IAEA / CRP Prompt Neutron / 13-16th Dec Initial input data needed Example from Varapai’s thesis (2006) / Experiment performed on 252Cf(sf) at IRMM (Belgium) Ionisation chamber NE213 Y(A,KE,Z)=Y(A) × Y(,  KE ) × Y(Z) Mass and KE distributions Mass Yield  KE Nuclear charge distribution Initial data needed for the code

5 IAEA / CRP Prompt Neutron / 13-16th Dec Nuclear charge distribution Most probable charge Z P taken from Walh evaluation and/or from systematic Charge dispersion:  z assumed independent of the mass Wahl, Phys. Rev. 126 (1962) 1112 Sampling of a fission fragment (A, Z) with a kinetic energy KE Y(A,KE,Z)=Y(A) × Y(,  KE ) × Y(Z) These are the initial data needed for the code Mass and KE distributions: taken from Varapai’s thesis work Initial input data needed

6 IAEA / CRP Prompt Neutron / 13-16th Dec Sampling of the light fragment: 1 The mass and charge of the heavy fragment can be deduced: A H =252-A L Z H =98-Z L Its kinetic energy (KE H ) is sampled on the experimental kinetic energy distribution 2 Calculation procedure A L, Z L, KE L A H, Z H, KE H Total Kinetic Energy (From Audi-Wapstra) Total Excitation Energy The Total Excitation Energy (TXE) available at scission can be deduced: 3

7 IAEA / CRP Prompt Neutron / 13-16th Dec At scission: After full acceleration of the FF: Calculation procedure 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)) The FF are considered as a Fermi gas, the intrinsic excitation energy can therefore be written as: This intrinsic excitation energy will be used for the prompt neutron and gamma emissions Partitioning of the excitation energy between the two fragments 4

8 IAEA / CRP Prompt Neutron / 13-16th Dec Calculation procedure Asymptotic level density parameter Effective excitation energy Shell corrections (Myers-Swiatecki, …) Level density parameter calculated from Ignatyuk’s model: Nuclear Temperature: R T =T L /T H R T =1 R T = / / / 174 R T =R T (A)

9 IAEA / CRP Prompt Neutron / 13-16th Dec Rotational Energy: E Rot  : quadrupole deformation taken from Myers-Swiatecki J : Moment of Inertia : Three available options in FIFRELIN Rigid body Irrotational flow (Approximation of the rotational energy) Calculation procedure Microscopic calculations from CEA-DAM (AMEDEE database) (on going) Data taken from: phynu.cea.fr/science_en_ligne/carte_potentiels_micro scopiques/carte_potentiel_nucleaire.htm

10 IAEA / CRP Prompt Neutron / 13-16th Dec J: Angular momentum: Two available options (Vandenbosch – Huizenga) (Wilhelmy et al., Phys. Rev. C5, 2041 (1972)) Calculation procedure  : spin cut-off U : effective excitation energy corrected for pairing:

11 IAEA / CRP Prompt Neutron / 13-16th Dec Example: Initial conditions in the plane (E*,J) obtained for the light and heavy primary fragments 252 Cf(sf) Calculation procedure Heavy Light (J=0.5J rigid )

12 IAEA / CRP Prompt Neutron / 13-16th Dec Weisskopf spectrum where T is the temperature of the residual nucleus: Neutron evaporation Calculation procedure 5 Energy limit for the neutron emission: E* J

13 IAEA / CRP Prompt Neutron / 13-16th Dec Prompt gamma emission Calculation procedure 6 Implementation of gamma cascade simulation methods which can be applied to a vast domain of isotopes Implementation of several nuclear models (level density, strength function, spin cutoff, density parameter...) First tests on single isotopes providing deexcitation spectra and multiplicities Preliminary spectra for 252 Cf spontaneous fission From D. Regnier, Workshop Novi Sad Nov. 2011

14 IAEA / CRP Prompt Neutron / 13-16th Dec R T  L  H E * lim inertia L H tot 1.00SnSn SnSn Vorobyev et al. (2004) With R T =1 and E lim =Sn (no rotational energy) ( ): Saw-tooth not reproduced and more neutrons are emitted from heavy fragment (in conflict with experiment)  (A) Results 252Cf(sf) With R T =1.25 and E lim =Sn (no rotational energy) ( ): Ratio L / H in better agreement with experiment

15 IAEA / CRP Prompt Neutron / 13-16th Dec R T  L  H E * lim inertia L H tot 1.25S n +E rot J=J Rigid S n +E rot J=J Irrot S n +E rot J=0.5*J Rigid Vorobyev et al. (2004) Strong impact of the rotational energy: With rigid model ( ): overestimation of the total neutron multiplicity With fluid model ( ): completely wrong! With J=0.5 J Rigid ( ): more satisfactory  (A) Results 252Cf(sf)

16 IAEA / CRP Prompt Neutron / 13-16th Dec R T  L  H E * lim inertia L H tot R T (A)S n +E rot J=0.5J Rigid Vorobyev et al. (2004) With a temperature ratio depending on A (R T =R T (A)): Reasonable agreement with the experimental data except in the [ ] mass region Average multiplicities are very well reproduced  (A) Results 252Cf(sf)

17 IAEA / CRP Prompt Neutron / 13-16th Dec Good agreement with Budtz-Jorgensen data except in the very high TKE energy (could be due to scission neutron (see Kornilov 2004)) Slope: In agreement with Budtz (88) and Nifenecker (73) Strong differences are observed between Light and heavy fragments  (TKE) Results 252Cf(sf)

18 IAEA / CRP Prompt Neutron / 13-16th Dec Results 252Cf(sf) From O. Litaize, Novi Sad, Nov. 2011)

19 IAEA / CRP Prompt Neutron / 13-16th Dec Results 252Cf(sf) From O. Litaize, Novi Sad, Nov. 2011)

20 IAEA / CRP Prompt Neutron / 13-16th Dec  (A) Good agreement with Budtz data, except in [ ] mass region Discrepancy also observed by Kornilov (2007) and Lemaire (2005) Results 252Cf(sf)

21 IAEA / CRP Prompt Neutron / 13-16th Dec Neutron Spectrum in the Laboratory Could be improved by accounting for the Energy dependence of the inverse process of compound nucleus formation in the Weisskopf spectrum (going on) Nice agreement between 0.5 and 7 MeV (within 5%) = 2.13 MeV (Reference) = 2.14 MeV (This work) Results 252Cf(sf)

22 IAEA / CRP Prompt Neutron / 13-16th Dec Heavy Light Total P  Good agreement with Vorobyev’s data Results 252Cf(sf)

23 IAEA / CRP Prompt Neutron / 13-16th Dec = 7.06 ± 0.35 (Pleasonton-2001) = 6.7 ± 0.4 (Nardi-1973) = 6.84 ± 0.3 (Verbinski-1973) = 7.08 MeV (Fréhaut-89) = 6.77 MeV (This work)  E  (A) Results 252Cf(sf)

24 IAEA / CRP Prompt Neutron / 13-16th Dec Talou et al., PHYSICAL REVIEW C 83, (2011) C. Manailescu et al., Nuclear Physics A867 (2011) / / 120 Temperature ratio law Results 239Pu(n,f) Fifrelin 108 / 132

25 IAEA / CRP Prompt Neutron / 13-16th Dec Pu(n,f)) Initial Input Data (Wagemans) Results 239Pu(n,f)

26 IAEA / CRP Prompt Neutron / 13-16th Dec Pu(n,f)) Initial Input Data (Wagemans) Results 239Pu(n,f)

27 IAEA / CRP Prompt Neutron / 13-16th Dec Pu(n,f)) Initial Input Data (Wagemans) Results 239Pu(n,f)

28 IAEA / CRP Prompt Neutron / 13-16th Dec Pu(n,f)) Mass yield (post neutron): Comparaison Fifrelin / Measurements performed at ILL on Lohengrin mass sepctrometer) Results 239Pu(n,f)

29 IAEA / CRP Prompt Neutron / 13-16th Dec JEFF 3.1.1Fifrelin Total energy less the energy of neutrinos / MeV MeV Kinetic energy of fragments (post-neutron) / MeV MeV Total energy released by the emission of "prompt" gamma rays / MeV6.69 MeV Total energy released by the emission of "prompt" neutron / MeV6.00 MeV Average prompt neutron multiplicity 2.87 n/f2.92 n/f Mean neutron energy in Lab 2.11 MeV2.05 MeV Results 239Pu(n,f) 239 Pu(n,f))

30 IAEA / CRP Prompt Neutron / 13-16th Dec Results Comparison 239Pu(n,f) / 240Pu(sf) 239Pu(n,f): Wagemans et al. 240Pu(sf): Dematte et al. Initial Data: Same fissioning nucleus, but with different excitation energy

31 IAEA / CRP Prompt Neutron / 13-16th Dec A Monte Carlo code has been recently developed in order to investigate prompt fission neutrons and gamma properties. The available excitation energy of the fission fragments used for neutrons and gamma emission is calculated by accounting for their rotational energies. The fission fragment evaporation process is simulated using two main assumptions: (i) the partitioning of the excitation energy between primary fragments is performed by adopting a mass dependent temperature ratio law which has been established from physical grounds; (ii) a spin dependent excitation energy limit is considered for neutron emission. The main features of the prompt neutrons (energy spectrum, average neutron multiplicity, distribution of the prompt neutron multiplicity …) as well as the excitation energy available for prompt-gamma emission are nicely reproduced. Conclusion

32 IAEA / CRP Prompt Neutron / 13-16th Dec We plan to upgrade the code by: Accounting for realistic fission fragment moment of inertia (going on by using AMEDEE database) Accounting for the inverse process of compound nucleus formation involved in the Weisskopf spectrum (going on) Temperature ratio law: depending on the mass and the fission modes (Standard I and II) Possible additional neutron source (scission neutron) The treatment of the gamma emission in order to get the prompt gamma spectrum (going on) Outlook

33 IAEA / CRP Prompt Neutron / 13-16th Dec S. Lemaire et al., [Phys. Rev. C, 72(2), (2005)];  hypothesis H1: R T =T L /T H =1: doesn’t work  hypothesis H2: partitioning of the excitation energy between the two fragments from experimental data: (A), (A) and (A): less predictive P. Talou et al., [CNR 2009] R T values for each fission mode P. Talou et al., Phys. Rev. C83, (2011) Randrup and Vogt, [Phys. Rev. C80, , Phys. Rev. C80, , (2009)] Similar Monte Carlo codes already exist: Annexe

34 IAEA / CRP Prompt Neutron / 13-16th Dec  (A,TKE) Annexe

35 IAEA / CRP Prompt Neutron / 13-16th Dec Annexe

36 IAEA / CRP Prompt Neutron / 13-16th Dec Influence of the RT law on neutron multiplicity Exemple: 240Pu(sf) Annexe