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

Motivation experiments 124 Xe( N/Z=1.30 )+Pb and 136 Xe( 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 codesextensive data base for comparison with up-to-date parameterizations and/or codes unique experimental information to investigate the properties of highly excited nuclear systemunique experimental information to investigate the properties of highly excited nuclear system to test/improve their predictions for RIB facilities relevant for many astrophysical scenarios: supernovae explosions (formation of elements), properties of neutron stars…

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 investigation of the isoscaling phenomenon in the broad Z range in the relativistic energy regime and extraction of the symmetry energy coefficient R.J.Charity, Phys. Rev. C 58 (1998), 1073 evaporation ->shifts the final isotopic distributions towards residue corridor

The experimental set-up

Fragment Separator (FRS) – a high-resolution magnetic spectrometer  high resolving power: ToFdE in ionisation chamber position in scintillators mass identification: Z/ΔZ ~ 200 A/ΔA ~ 400 inverse kinematicsin-flight identification

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

Experimental resultscross sections, comparison with EPAX Experimental results I – cross sections, comparison with EPAX

Measured cross sections  124 Xe+Pb 1 A GeV  136 Xe+Pb 1 A GeV

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

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

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

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

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 /Z of experimental data

Break-up and backtracking of E* from evaporation break-up abrasion experimental data evaporation 136 Xe  knowing final /Z and N/Z of the projectilethe length of the evaporation process may be traced back  knowing final /Z and N/Z of the projectile the length of the evaporation process may be traced back from E*=aT f 2 temperature determines the length of the evaporation cascade ‹N›/Z~N/Z proj

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

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

Isoscaling from 136 Xe and 124 Xe data overall the isoscaling very well respected over the broad nuclear charge range  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

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

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

Conclusions  isotopic distributions in the broad Z range were obtained for residues from 136 Xe (N/Z=1.52) and 124 Xe (N/Z=1.30) projectiles final /Z reveal sensitivity to the length of an evaporation cascade following the nuclear break-up  isoscaling phenomenon observed in the broad Z range from residues with Z=10-13 the symmetry energy coefficient γ app =14±3 MeV was extracted comparison with SMM calculations supports decrease of symmetry coefficient for hot fragments T f ~ 5-8 MeV for 136 Xe T f ~ 4 MeV for 124 Xe  comparison with EPAX suggests slight underestimation of less n-rich isotopes in the vicinity of 136 Xe 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 /Z may be reproduced additional refinement of the code needed before the realistic quantitative result may be deduced