1. 1 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Olivier SEROT Commissariat à lEnergie Atomique – Centre de Cadarache Direction pour lEnergie Nucléaire / Département dEtudes des Réacteurs / Service de Physique des Réacteurs et du Cycle / Laboratoire dEtudes Physiques Prompt neutron emission from Monte Carlo simulation

2. 2 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Prompt neutron emission from Monte Carlo simulation Introduction Initial input data needed Calculation procedure Preliminary results Olivier LITAIZE + Olivier SEROT / CEA-Cadarache / DEN Collaborations 252Cf(SF)

3. 3 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 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: (A,TKE), P( ), E (A), N(,A)…. Test models related to the emission process Introduction

4. 4 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 S. Lemaire et al., [Phys. Rev. C, 72(2), 024601 (2005)]; hypothesis H1: R T =T L /T H =1: doesnt work hypothesis H2: partitioning the excitation energy between the two fragments from experimenatl data: (A), (A) and (A): less predictive P. Talou et al., [CNR 2009] R T values for each fission mode Randrup and Vogt, [Phys. Rev. C80, 044611, 2009 + Phys. Rev. C80, 024601, (2009)] Similar codes already exist: Introduction

5. 5 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Thèse N. Varapai, Université Bordeaux 2006 Ionisation chamber NE213 Y(A,KE,Z)=Y(A) × Y(, KE ) × Y(Z) Initial input data / 252Cf(SF) Allow to sample the mass, charge and KE of the fission frament Mass and KE distributions from Varapais thesis work

6. 6 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Allow to sample the mass, charge and KE of the fission frament Mass and KE distributions from Varapais thesis work Nuclear charge distribution Most probable charge taken from Walh evaluation: Z P Charge dispersion: z assumed independent of the mass Y(A,KE,Z)=Y(A) × Y(, KE ) × Y(Z) From Wahl, Phys. Rev. 126 (1962) 1112 Initial input data / 252Cf(SF)

7. 7 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Sampling of the light fragment: A L, Z L, KE L Total Kinetic Energy Total energy Total Excitation Energy 1 Then, the mass and charge of the heavy fragment are deduced: A H =252-A L Z H =98-Z L Its kinetic energy (KE H ) is sampled on the experimental kinetic energy distribution A H, Z H, KE H 2 3 The Total Excitation Energy (TXE) available at scission can be deduced: Calculation procedure

8. 8 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Level density parameter Asymptotic level density parameter Effective excitation energy Shell corrections (Myers-Swiatecki, …) Ignatyuks model 4 Partitioning of the excitation energy between the two fragments Calculation procedure 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)): n n n ~10 -20 s ~10 -17 s ~10 -14 s scission fully acc. FF Neutron emission gamma emission

9. 9 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Weisskopf spectrum where T is the temperature of the residual nucleus: 5 Neutron evaporation Energy limit for the neutron emission: : Myers-Swiatecki Spin distributions Inertia momentum Appoximation of the rotational energy E rot allows to simulate competition neutron-gamma (Vandenbosch – Huizenga) B= 8 forl LF B=9 for HF Calculation procedure

10. 10 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Modèle R T L H E * lim inertie L H tot L H A1.00SnSn - 1.82 2.444.2615.7918.11 B1.25SnSn -2.281.934.2119.6414.23 Vorobyev et al. (2004)2.051.703.76-- With model A: saw-tooth not reproduced and more neutrons from heavy fragment With model B: ratio L : H in better agreement with experiment Preliminary results

11. 11 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Modèle R T L H E * lim inertie L H tot L H C1.25S n +E Yrast J rigid 2.161.854.0119.6514.24 D1.25S n +E Yrast J fluid 1.060.461.5219.6614.24 E1.25S n +E Yrast 0.4 J rigid 1.981.713.6919.6414.22 Vorobyev et al. (2004)2.051.703.76-- Strong impact of the rotational energy: With rigid model: overestimation of the total neutron multilplicity With fluid model: completely wrong! Intermediate: satisfactory Preliminary results

12. 12 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Preliminary results Modèle R T L H E * lim inertie L H tot L H F R T (A)=0.0116A S n +E Yrast 0.4 J rigid 2.081.703.7819.6614.28 GR T (A)S n +E Yrast 0.4 J rigid 2.061.703.7619.8914.27 Vorobyev et al. (2004)2.051.703.76-- Model G: R T =T L /T H Model F (test)

13. 13 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Preliminary results (A,TKE) (model G)

14. 14 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Preliminary results (A) (model G) Reasonable agreement except in the [155-170] mass region

15. 15 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Preliminary results (TKE) (model G) Contributions of the light and heavy fragment needed to understand the (TKE) behaviour Reasonable agreement except in the very high TKE energy

16. 16 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 (A) (modèle G) Preliminary results

17. 17 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Preliminary results P ( ) model G Léger Lourd Total Modèle G: Vorobiev: Reasonable agreement Modèle R T L H E * lim inertie L H tot L H GR T (A)S n +E Yrast 0.4 J rigid 2.061.703.7619.8914.27 Vorobyev et al. (2004)2.051.703.76--

18. 18 Workshop Espace de Structure Nucléaire Théorique / 12-16 April, 2010 Energy spectrum in the lab. (modèle G) = 2.13 MeV (Budtz) = 2.20 MeV (modèle G) Maxwellienne (T=1.42 MeV): Modèle G : Preliminary results