Recent results on the symmetry energy from GANIL A.Chbihi GANIL Why studying E sym in Fission Extracting E sym from isotopic distribution of FF Influence of neutron evaporation Application to fission data (VAMOS + Spider) Application to more dissipative reactions (VAMOS+INDRA) Probing the Symmetry energy in fission & dissipative reactions NuSym2015A. Chbihi1

Why studying Esym in binary fission Process of fission Low energies : – eliminate the pre-equilibrium emission Strongly constrained by mass and charge conservation : – most part of the system is contained in the 2 fission fragments (Ztot ≈ Z1+Z2)  Facilitate the experimental extraction of E sym  Extend the fission study to more complicated cases: dissipative reactions and multifrgamentation 2NuSym2015A. Chbihi

W.A. Friedman prescription Isotopic yield & isoscaling in fission Maximum of the isotopic distribution : 1 st derivative of BE W.A. Friedman PRC 29, R 2004 Width of the isotopic distribution : 2d derivative z1/a1 = z2/a2 = Z/A Dominant term (n-z) 2 /a 3NuSym2015A. Chbihi

Test of the method Fission fragments of 234 U 4 T = 1.7, 1.8, 1.9 MeV NuSym2015A. Chbihi

Test of the method 5 From this Eq. we can deduce the symmetry energy term if the width of the isotopic yield distribution is known : C sym = 23 MeV, shifted by (Z=30) & 2. (Z=62) Peak position: shift of 1 u (1 neutron), whole LDM NuSym2015A. Chbihi

GEneral Fission Model GEF We use the general Fission Model GEF, developed by B. Jurado and K.-H. Schmidt, in order to generate a data set of fission fragments induced by the excitation of 250Cf at E* = 50 MeV. Then we fitted the isotopic distributions with a Gaussian functional and applied the Friedman Eq. as : 6NuSym2015A. Chbihi

7 GEF, fission of 250 E* = 50 MeV, isotopic distribution before neutron evaporation The temperature is deduced from the E* assuming Fermi gas with a=A/8 (T= 1.24 MeV) One can observes that Esym = MeV, = 23 MeV An increase of Esym aroud Z FF = 53 and 39 NuSym2015A. Chbihi

8 GEF, fission of 250 Cf, post n, after neutron evaporation Esym is reduced to 19 MeV for Z FF = 30 and to 11 MeV for 64 An increase of Esym around Z FF = 54 and 37 NuSym2015A. Chbihi

Experiment M. Caamaño et al., PRC88, (2013) 9 Experiment performed at GANIL 238 U+ 12 E/A = 6.5 MeV The exit channel of 250 Cf fission has been selected (SPIDER) Fission fragments of 250Cf was identify in A&Z with high resolution (VAMOS) Excitation energy was estimated to be E* = 50 MeV Spider : 35-55° (  gr (C)=31°) Annular Si Tel. to detect TLF Vamos rotated 20° Detect & identify in A,Z FF NuSym2015A. Chbihi

Experimental results 10 Fit of the isotopic distribution of fission fragments with Gaussian functional Fit of the isotopic distribution of Z = 43 and 55 with Gaussian functional NuSym2015A. Chbihi

11 Esym at 12 MeV for Z FF < 45 and then decreases to 8 MeV The values of Esym < standard value of 23 MeV From GEF calculation the decrease of Esym is due to the neutron evaporation, For this experiment the decrease of Esym is due to neutron emission but not only DEFORMATION EFFECT ? Experimental results Extraction of Esym from the width of the isotopic distribution NuSym2015A. Chbihi

Reduction factor of E sym 12 Difference: E sym (GEF pre neutron) - E sym (post neutron) Difference: Esym (GEF pre neutron) – E sym (experiment) Average Reduction due to neutron evaporation = 25 % Average Reduction GEF vs Exp. = 55 % NuSym2015A. Chbihi

13 M.K. GAIDAROV et al., PRC85, (2012) oblate prolate E sym of deformed n-rich nuclei Very neutron-rich Kr Approach that combines deformed HF +BCS method with Skyrme-type density dependent eff. inter. and CDFM (Coherent Density Fluct Model) Peak of E sym semi magic 86 Kr (N=50) and 118 Kr (N=82) Reduction of Esym at maximum deformation whatever the interaction Quadrupole parameter NuSym2015A. Chbihi

Post-scission neutron multiplicities Characterization in A and Z of FF is derived from the scission point model of B.D. Wilkins (PRC14, 1832, (1976)). Assumption : the scission configuration is the one that minimizes the total energy of the FF Derivative of Etot : 14 M. Caamaño et al., PRC88, (2013) NuSym2015A. Chbihi

/Z of fission fragments at the scission 15 E sym E sym *0.57 Courtesy of F. Farget Experimental Neutron excess before evaporation Comparison to Scission Point Model (LD) with standard Esym with Esym*0.57 NuSym2015A. Chbihi

NuSym2015 A. Chbihi INDRA Q1 Q2 Dipole beam detection INDRA in coincidence LCP /IMF event characterization (b, excitation energy) 16 Symmetry energy experiments 40 Ca + 40 E/A = 35 MeV 40 Ca + 48 E/A = 35 MeV isospin diffusion 48 Ca + 40 E/A = 35 MeV isospin diffusion 48 Ca + 48 E/A = 35 MeV For B  (Tm)= 2.2, 2.12, 1.957, 1.80, 1.656, 1.523, 1.401, 1.289, 1.186, 1.091, 1.004, 0.923, 0.849, 0.782, 0.719, VAMOS PLF (E503) High Isotopic Resolution

Isotopic distributions of PLF & of reconstructed primary fragments NuSym2015A. Chbihi Derive an expression similar to Friedman adapted to more dissipative collisions 17 A primary - N free A PLF M. Boisjoli thesis Nov 2013 A.C et al., ARIS

Prescription of A. Raduta & F.Gulminelli 18 A. Raduta and F. Gulminelli, PRC75, , (2007) In the framework of MMM Csym directly inferred from width of Isotopic dist in Grand-canonical approximation A Gaussian approximation on GC leads to NuSym2015A. Chbihi

Conclusion Study of E sym in Fission with help of GEF allows to evaluate – Effect of neutron evaporation on Esym – Effect of deformation of n-rich nuclei on Esym – Extraction of Esym from variance of ID Application to more dissipative reactions (VAMOS+INDRA) Work on progress… 19NuSym2015A. Chbihi

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56-70 Ni 10 5 pps A.MeV FAZIA/ 12 blocks (192) 2°-14° Tracking detectors (CATS) Possible setup Must2 14°- 58° 122°-166° Must2 δ = (N-Z)/A = 0.2, for 70 Ni δ = 0.0 for 56 Ni Fazia 2°-14° : isotopic distributions of the PLF in coinc with LCP in Fazia and Must2 provide the primary isotopic distribution  E sym, Isospin diffusion. Must2 14°- 58° and 122°-166° (it covers the MR region (90° CM)) : correlation function for space-time characterization of sources estimation of the density around the projectile and MR In-medium short-lived nuclei as well as out-of-medium NuSym2015A. Chbihi21

NuSym2015A. Chbihi22 Possible systems Proj-target combination either very: n-rich or different asym n/z

GEF model The model has been developed with the aim to provide dedicated nuclear data for applications in nuclear technology and engineering. The code treates spontaneous fission and fission up to an excitation energy of about 100 MeV (including multi-chance fission) for a wide range of heavy nuclei from polonium to seaborgium. The development of GEF has been supported by the European Union in the framework of the EFNUDAT and the ERINDA projects and by the OECD Nuclear Energy Agency. A detailed description of the code is given in this report. EFNUDATERINDAthis report 23NuSym2015A. Chbihi