Daniela Henzlova GSI-Darmstadt, Germany on leave from NPI Rez, Czech Republic

1. Systematic Investigation of the Isotopic Distributions Measured in the Fragmentation of 124Xe and 136Xe Projectiles Daniela Henzlova GSI-Darmstadt, Germany on leave from NPI Rez, Czech Republic

2. Motivation • experiments 124Xe(N/Z=1.30)+Pb and 136Xe(N/Z=1.52)+Pb at 1 A GeV performed at FRS allow to identify final residues over broad range of nuclear charge and to study the sensitivity of their isotopic composition to the N/Z of the projectile • extensive data base for comparison with up-to-date parameterizations and/or codes • to test/improve their predictions for RIB facilities • unique experimental information to investigate the properties of highly excited nuclear system • relevant for many astrophysical scenarios: supernovae explosions (formation of elements), properties of neutron stars…

3. Main aims • extraction of isotopic cross sections in the broad range of Z and comparison with EPAX parameterization and ABRABLA code predictions • investigation of influence of cluster emission during evaporation and of thermal conditions after nuclear break-up on the isotopic composition of the final residues – deviation from the residue corridor • evaporation -> shifts the final isotopic distributions towards residue corridor R.J.Charity, Phys. Rev. C 58 (1998), 1073 • investigation of the isoscaling phenomenon in the broad Z range in the relativistic energy regime and extraction of the symmetry energy coefficient

4. The experimental set-up

5. Fragment Separator (FRS) – a high-resolution magnetic spectrometer inverse kinematics in-flight identification mass identification: position in scintillators dE in ionisation chamber ToF Z/ΔZ ~ 200 A/ΔA ~ 400 • high resolving power:

6. mass resolution with FRS 136Xe + Pb 1A GeV 124Xe + Pb 1A GeV 136Xe 124Xe

7. Experimental results I – cross sections, comparison with EPAX

8. Measured cross sections • 136Xe+Pb 1 A GeV • 124Xe+Pb 1 A GeV

9. Comparison with EPAX – isotopic distributions I • EPAX = empirical parameterization of the fragmentation cross sections • 136Xe+Pb 1 A GeV EPAX for 136Xe+Pb • 124Xe+Pb 1 A GeV EPAX for 124Xe+Pb • underestimation of production cross sections of lighter isotopes • slight underestimation of cross sections of isotopes on the less n-rich side of the isotopic distributions in case of 136Xe projectile

10. Comparison with EPAX – mean N-over-Z 136Xe • 136Xe+Pb 1 A GeV • 124Xe+Pb 1 A GeV EPAX for 136Xe+Pb EPAX for 124Xe+Pb 124Xe • slightly higher <N>/Z in the vicinity of the 136Xe projectile • scarcer data available for 136Xe projectile when EPAX was formulated • low values of <N>/Z of the residues far from both projectiles • too fast removal of the memory on the initial isotopic composition • present data may be used to refine the EPAX parameterization

11. Experimental results II – mean N-over-Z, thermal conditions at break-up

12. <N>/Z in full nuclear charge range 136Xe • 136Xe+Pb 1 A GeV • 124Xe+Pb 1 A GeV 124Xe • <N>/Z investigated in the broad nuclear charge range • cold residues preserve memory on the initial N/Z over the whole nuclear charge range (high excitation energies) residue corridor not reached

13. Comparison with ABRABLA – abrasion+evaporation and influence of the cluster emission • n, p, alpha emission -> too strong removal of memory on initial N/Z • implementation of cluster emission (IMF) memory on initial N/Z not completely removed not sufficient to reproduce <N>/Z of experimental data

14. Break-up and backtracking of E* from evaporation 136Xe experimental data abrasion ‹N›/Z~N/Zproj break-up ‹N›/Z~N/Zproj evaporation • knowing final <N>/Z and N/Z of the projectilethe length of the evaporation process may be traced back from E*=aTf2 temperature determines the length of the evaporation cascade

15. Comparison with ABRABLA – influence of the thermal conditions at the freeze-out of the break-up • <N>/Z of residues from 124Xe less sensitive to length of evaporation cascade • less n-rich projectile final isotopic distribution closer to residue corridor • only including the nuclear break-up allows to reproduce <N>/Z of the final residues Tf=5-8 MeV and 4 MeV for 136Xe and 124Xe, respectively • final <N>/Z reflects the thermal conditions at the freeze-out

16. Experimental results III - isoscaling and coefficient of symmetry energy

17. Isoscaling from 136Xe and 124Xe data • overall the isoscaling very well respected over the broad nuclear charge range • a slight deviation from strictly exponential trend in the vicinity of projectile Z due to increasingly nongaussian shape of the isotopic distributions

18. Exponent of isoscaling from 136Xe and 124Xe data • initial decrease consistent with production of large fragments by evaporation process at small excitation energy • extraction of symmetry energy coefficient residues produced in the multifragment event isoscaling exponent in charge range Z=10-13: α = 0.36±0.01

19. Extraction of symmetry coefficient • by A. Botvina et al. the following relation between the exponent α and the symmetry energy coefficient γ was derived: Isotopic composition of projectiles Experimental isoscaling temperature of disintegrating system • temperature assumed T ~ 4-6 MeV • in the relativistic energy regime change of Z/A in the abrasion negligible ~ projectile γapp=14±3 MeV • symmetry energy coefficient of residues Z=10-13: • investigation of influence of evaporation with SMM code suggests γreal even lower than γapp • symmetry energy coefficient lower than for cold heavy nuclei, where typically γ~21-25 MeV

20. Conclusions • isotopic distributions in the broad Z range were obtained for residues from 136Xe (N/Z=1.52) and 124Xe (N/Z=1.30) projectiles • comparison with EPAX suggests slight underestimation of less n-rich isotopes in the vicinity of 136Xe projectile and too strong removal of memory on the initial N/Z present data may serve to refine the EPAX formulation • comparison with ABRABLA suggests that only upon introducing nuclear break-up final <N>/Z may be reproduced final <N>/Z reveal sensitivity to the length of an evaporation cascade following the nuclear break-up additional refinement of the code needed before the realistic quantitative result may be deduced Tf ~ 5-8 MeV for 136Xe Tf ~ 4 MeV for 124Xe • isoscaling phenomenon observed in the broad Z range from residues with Z=10-13the symmetry energy coefficient γapp=14±3 MeV was extracted comparison with SMM calculations supports decrease of symmetry coefficient for hot fragments