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A new statistical scission-point model fed with microscopic ingredients

CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006. Workshop on the Theories of Fission and Related Phenomena ESNT Workshop May 9- 12, 2006. A new statistical scission-point model fed with microscopic ingredients.

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A new statistical scission-point model fed with microscopic ingredients

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  1. CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Workshop on the Theories of Fission and Related Phenomena ESNT Workshop May 9- 12, 2006 A new statistical scission-point model fed with microscopic ingredients Sophie Heinrich CEA/DAM-Dif/DPTA/Service de Physique Nucléaire

  2. CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 A new statistical scission-point model Preamble Our goal: To reconsider the original Wilkins scission-point model (1976) in order to provide some fission fragments properties, sustaining it with microscopic ingredients, and avoiding ad hoc parameters. (Thesis work)

  3. CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Fundamental Hypothesis • Observations: • Wide amplitude process • Dramatic importance of shell effects of the fission fragments. • Reorganization of the nucleus internal structure • System’s “history” is simulated by a statistical equilibrium at the scission point. Static Approach

  4. CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Why a renewal of the static approach ? • Many reachable observables • We have: • Experimental data with new insight (exotic nuclei, super heavy nuclei) and wide energy range (SPIRAL , GSI, …) • A need of predictions for nuclear data • (used directly or as a guide for reaction models) • We should provide: • Fission fragments distributions (mass, energy …) • Fragments properties (deformation, isospin …) • Without phenomenological ajustement.

  5. CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Why a renewal of the static approach ? • Possible improvements to scission-point model • Huge increase in computer processing power (CCRT, Ter@tec) • Very goodmicroscopicdescription for individual (deformed) energy levels • New level densities • Better comprehension of scission-point features

  6. Fission fragments distributions are entirely determined at ScissionPointby the energy available in the system of the complementary fragment pairs... Tips distance Heavy fragment Light fragment bL bH CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Scission-point Model Energy at the scission point = Individual microscopic energy (HF + Gogny force)for each fragments +Nuclear interactionbetween the 2 fragments +Coulombian interactionbetween the 2 fragments Available Energy of the system = E( compound system before fission ) – E( scission ) • If scission point can be precisely characterized, there is no more ajustable parameter !

  7. Available energy: • Phase space: • Relative probability of a given fragment pair : Wilkins et al. CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Basic equation

  8. Tips Distance D Heavy fragment Light fragment bL bH CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Scission-point Model • If we can precisely evaluate D at the scission point, there is no more adjustable parameters.

  9. CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Tips-Distance Effect Evolution of 228Th distributions D = 1fm to 10fm How to choose D ???

  10. Fusion path CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Fission Path Potential barrier Exit Point S P ~ D

  11. D ~ 4 to 6fm radius (fm) Q20 Z Axis (fm) CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Correlation between Scission-point and Exit-point • Selection of the Exit Points : • Strong modification of total binding energy • Hexadecapolar moment drop • Nucleon density at the neck < 0.01 nuc.fm-3 : Fit on 2 ellipsoids

  12. Direct access to mass and charge yields. Outline of involved deformations. Mass and charge distributions 228 Thorium D = 5fm Excitation energy of fissioning nucleus = 10MeV CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006

  13. K-H. Schmidt et al. CEA DAM/DPTA/SPN/MED/Sophie Heinrich Journées de physique nucléaire 2006 222->228Thorium N=132 Competition between the symmetric and the asymmetric fission for isotopes from A=222 to A=228. N=134 N=136 N=138

  14. Mean Values X CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006

  15. Average kinetic energy for one fragment CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Total Kinetic Energy : <Vcoul + Vnuc> Z 5U A A

  16. CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Average TKE of a specific fragment pair We can pick a specific fragment pair … … and calculate the TKE of the system distribution.

  17. Average excitation energy of one fragment with respect to the mass Saw-tooth curve CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Average deformation and excitation energies Z Average deformation of one fragment A A

  18. What have we learned ? • Peak width too short: needs dynamical consideration. CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 • Spherical/deformed and proton/neutron shell effects are well reproduce (Gogny force works fine). • Most probable configurations: reliable predictions for nuclear data with a parameter coming from microscopic calculation. • Many observables are available : mean TKE, mean excitation energy,... and can be used for further evaluations (number of emitted neutron, …) • We still suffer from a lack of description about what happens before the scission-point (prescission energy, emission of particules,…).

  19. Still to be done : CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 • Try out microscopic level densities. • Include temperature microscopic calculation (no more shell effect). • Rethink the whole definition of scission point.

  20. J.L. Sida (PhD Director) H. Goutte J.F. Berger M. Girod S. Hilaire P. Romain B. Morillon P.Morel M. Dupuis F. Chappert Cast & Crew : CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Thanks ...

  21. Generalized Superfluid Model :Critical energy, critical temperature, …etc, corresponding to phase transition between normal and superfluid phase. Level Density: Level Density : G S M E > Ecrit : E < Ecrit : CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006

  22. Experimental results CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 • First interpretation : liquid drop fission… • Equal mass fragments : • Actually, we often observe a heavy and a light fragment… • We need to consider quantum effects

  23. Dynamical Calculations Exit Points Energy Elongation Asymmetry CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 Time dependant Potential Energy Surface Héloïse Goutte CEA/DAM Theoretical Nuclear Structure Lab. Multi-valley symmetric valley asymmetric valley

  24. Microscopic Description of the Nucleus N body physics Force N-N ? No direct calculation from QCD Can be resolved up to N = 10 - 12 For N >> 10 : approximation needed Naked force Effective force • Shell Model • Effective residual • interaction • Valence space • Symmetry • conservation • Mean field Approach • No core • Separation between • internal structure and • collective excitation • (mean field and beyond) PhenomenologicalEffective Force Zero range Finite range CEA DAM/DPTA/SPN/MED/Sophie Heinrich ESNT Workshop May 9-12 2006 1 Nucleus = N nucleons with strong interaction

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