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Olivier SEROT Commissariat à l’Energie Atomique – Centre de Cadarache

Prompt neutron emission from Monte Carlo simulation. Olivier SEROT Commissariat à l’Energie Atomique – Centre de Cadarache Direction pour l’Energie Nucléaire / Département d’Etudes des Réacteurs / Service de Physique des Réacteurs et du Cycle / Laboratoire d’Etudes Physiques.

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Olivier SEROT Commissariat à l’Energie Atomique – Centre de Cadarache

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  1. Prompt neutron emission from Monte Carlo simulation Olivier SEROT Commissariat à l’Energie Atomique – Centre de Cadarache Direction pour l’Energie Nucléaire / Département d’Etudes des Réacteurs / Service de Physique des Réacteurs et du Cycle / Laboratoire d’Etudes Physiques

  2. Prompt neutron emission from Monte Carlo simulation 252Cf(SF) • Introduction • Initial input data needed • Calculation procedure • Preliminary results Collaborations Olivier LITAIZE + Olivier SEROT / CEA-Cadarache / DEN

  3. Introduction • 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…) • Our aim is to develop a Monte Carlo code able to simulate statistical decay of the fission fragments: • Look at the physical quantities which can be assessed: n(A,TKE), P(n), Eg(A), N(e,A)…. • Test models related to the emission process

  4. Introduction Similar codes already exist: • S. Lemaire et al., [Phys. Rev. C, 72(2), 024601 (2005)]; • hypothesis H1: RT=TL/TH=1: doesn’t work • hypothesis H2: partitioning the excitation energy between the two fragments from experimenatl data: <n>(A), <e>(A) and <Eg>(A): less predictive • P. Talou et al., [CNR 2009] • RT values for each fission mode • Randrup and Vogt, [Phys. Rev. C80, 044611, 2009 + Phys. Rev. C80, 024601, (2009)]

  5. Initial input data / 252Cf(SF) Y(A,KE,Z)=Y(A) × Y(<KE>, sKE) × Y(Z) Allow to sample the mass, charge and KE of the fission frament Mass and KE distributions from Varapai’s thesis work Ionisation chamber NE213 Thèse N. Varapai, Université Bordeaux 2006

  6. Initial input data / 252Cf(SF) Y(A,KE,Z)=Y(A) × Y(<KE>, sKE) × Y(Z) Allow to sample the mass, charge and KE of the fission frament Mass and KE distributions from Varapai’s thesis work Nuclear charge distribution • Charge dispersion: • sz assumed independent of the mass • Most probable charge taken from Walh evaluation: ZP From Wahl, Phys. Rev. 126 (1962) 1112

  7. Calculation procedure 2 1 Then, the mass and charge of the heavy fragment are deduced: AH=252-AL ZH=98-ZL Its kinetic energy (KEH) is sampled on the experimental kinetic energy distribution AH , ZH , KEH Sampling of the light fragment: AL , ZL , KEL The Total Excitation Energy (TXE) available at scission can be deduced: 3 Total Kinetic Energy Total energy Total Excitation Energy

  8. ~10-20s ~10-17s ~10-14s n g g g n g g scission g fully acc. FF g Neutron emission n g gamma emission Calculation procedure Partitioning of the excitation energy between the two fragments 4 At scission: TXE=Eint+Edef The main part of the deformation energy is assumed to be converted into intrinsic excitation energy (Ohsawa, INDS 251(1991)): Ignatyuk’s model Level density parameter Asymptotic level density parameter Effective excitation energy Shell corrections (Myers-Swiatecki, …)

  9. Calculation procedure Neutron evaporation 5 • Weisskopf spectrum where T is the temperature of the residual nucleus: • Energy limit for the neutron emission: Spin distributions (Vandenbosch – Huizenga) B= 8 forl LF B=9 for HF • Appoximation of the rotational energy • Erot allows to simulate competition neutron-gamma Inertia momentum b: Myers-Swiatecki

  10. Preliminary results • With model A: saw-tooth not reproduced and more neutrons from heavy fragment • With model B: ratio nL:nH in better agreement with experiment

  11. Preliminary results • Strong impact of the rotational energy: • With rigid model: overestimation of the total neutron multilplicity • With fluid model: completely wrong! • Intermediate: satisfactory

  12. Preliminary results Model F (test) RT=TL/TH Model G:

  13. Preliminary results n(A,TKE) (model G)

  14. Preliminary results n(A) (model G) Reasonable agreement except in the [155-170] mass region

  15. Preliminary results n(TKE) (model G) Reasonable agreement except in the very high TKE energy Contributions of the light and heavy fragment needed to understand the n(TKE) behaviour

  16. Preliminary results <e>(A) (modèle G)

  17. Preliminary results P (n) model G Modèle G: Vorobiev: Reasonable agreement Total Léger Lourd n n n

  18. Preliminary results Energy spectrum in the lab. (modèle G) Maxwellienne (T=1.42 MeV): Modèle G: <E> = 2.13 MeV (Budtz) <E> = 2.20 MeV (modèle G)

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