Isotopically resolved residues produced in the fragmentation of 136 Xe and 124 Xe projectiles Daniela Henzlova GSI-Darmstadt, Germany on leave from NPI Rez, Czech Republic

Outline  introduction extraction of properties of highly excited nuclear system  the experimental set-up high-resolution magnetic spectrometer - Fragment Separator  experimental results /Z and extraction of nuclear temperature isoscaling and extraction of symmetry energy coefficient  summary

Introduction properties of nuclear system under conditions of extreme temperatures and densities relevant for many astrophysical scenarios: study the properties of highly excited system from the isotopic distributions of the final residues in the complete Z range abrasion participants projectile spectator target spectator supernovae explosions (formation of elements), properties of neutron stars relativistic heavy-ion collisions

Introduction width and position of the isotopic distributions of hot fragments determined by the physical conditions of the reaction: from initial isotopic distributions the properties of hot system may be extracted -> temperature (T)+symmetry coefficient ( γ) and initial N/Z γ = 25 MeV γ = 14 MeV SMM calculation A.S.Botvina et al., Phys. Rev. C 65 (2002),

Introduction only distributions of cold residues accessible experimentally evaporation -> follow the influence of evaporation on N/Z reconstruct the excitation energy ~ temperature the isospin-thermometer method affects both position and width isotopic distributions of final residues available BUT: deduce the temperature of hot system from the position of the final isotopic distributionsdeduce the temperature of hot system from the position of the final isotopic distributions R.J.Charity, Phys. Rev. C 58 (1998), 1073

 yield ratio of isotopes produced in reaction systems differing in N/Z exhibits exponential dependence on N or ZIntroduction M.B.Tsang et al., Phys. Rev. C 64 (2001) N \ Y 124 Sn+ 124 Sn (N,Z)\Y 112 Sn+ 112 Sn (N,Z)  exponent of isoscaling may be related to coefficient of symmetry energy strength of symmetry energy contribution in the nuclear binding of the hot fragments may be extracted isoscaling

The experimental set-up

Experimental complex at GSI, Darmstadt UNILAC SIS FRS 12 A MeV~1 A GeV ion source target

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

Fragment Separator (FRS) – a high-resolution magnetic spectrometer ±15 mrad in angle ±1.5% in momentum combination of several B settings to scan all N/Z and momenta   acceptance of the Fragment Separator intermediate focal plane final focal plane intermediate focal plane final focal plane

mass resolution with FRS 136 Xe + Pb 1A GeV 136 Xe Z N

Experimental results Mean N-over-Z ratio and the isospin-thermometer method

 memory on initial N/Z preserved over the whole nuclear charge range (high excitation energies) evaporation does not remove memory on the N/Z of the projectile /Z in full nuclear charge range /Z in full nuclear charge range 136 Xe 124 Xe  /Z investigated in the full nuclear charge range stability line

Excitation energy introduced in abrasion 136 Xe+Pb 1A GeV 124 Xe+Pb 1A GeV ABRABLA (abrasion+ablation) calculation excitation energy far above 3 MeV/A introduced  excitation energy far above 3 MeV/A introduced break-up of highly excited system shorter evaporation cascade

Break-up reflected in the final /Z  /Z of the residues sensitive to the length of the evaporation process explore this sensitivity to determine E* -> the isospin thermometer method  only inclusion of break-up reproduces isotopic composition of the data stability line

Backtracking of E* from evaporation   mass, E* and N/Z of the nucleus changes in each evaporation step due to the emission of nucleon or light cluster excited fragment follows certain rather well defined path in the chart of nuclides  knowing the final N/Z and N/Zafter break-up, the excitation energy may be traced back  knowing the final N/Z and N/Z after break-up, the excitation energy may be traced back break-up abrasion experimental data evaporation 136 Xe N/Z~N/Zproj

The isospin thermometer method E* available for evaporation E*=aT f 2 assume a common temperature at freeze-out 136 Xe TfTfTfTf Universal temperature in a broad range of Z evaporation T f = 3MeV T f = 4MeV T f = 5MeV T f = 7MeV  final /Z reflects the thermal conditions at the freeze-out N/Z~N/Z proj

Comparison of 136 Xe and 124 Xe  temperature at the freeze-out extracted from 124 Xe ~ 4MeV /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 projectilefinal isotopic distribution closer to residue corridor, isospin-thermometer method starts to saturate 136 Xe+Pb 1A GeV 124 Xe+Pb 1A GeV

Temperature dependence on N/Z hot liquid-drop model: J.Besprovany and S. Levit, Phys. Lett. B 217 (1989) 1  higher N/Z -> higher temperature  although different in absolute value, the results of the isospin- thermometer method are consistent with the hot liquid-drop model prediction 136 Xe 124 Xe

Experimental results Isoscaling and coefficient of symmetry energy

Isoscaling from 136 Xe and 124 Xe data  isoscaling observed in broad nuclear charge range  initial decrease consistent with production of large fragments by evaporation process at small excitation energy  isoscaling exponent in charge range Z=10-13: α ~ 0.35

Extraction of symmetry coefficient  symmetry energy coefficient lower than for cold heavy nuclei, where γ~21-25 MeV Experimental isoscaling Isospin- thermometer  in the relativistic energy regime change of Z/A in the abrasion negligible Isotopic composition of projectiles γ=11-14 MeV ~ projectile  temperature from isospin-thermometerT~4-5MeV  symmetry energy coefficient:

Influence of evaporation SMM calculation for γ=4,8,14,25 MeV and 136 Xe, 124 Xe E*/A=4 MeV experimentally value reproduced only with the symmetry coefficient of hot fragments γ ~ 12 MeV  experimentally value reproduced only with the symmetry coefficient of hot fragments γ ~ 12 MeV  evaporation affects the exponent of isoscaling but does not remove its dependence on γ by A.Botvina

Comparison with /Z  decrease of symmetry coefficient for hot fragments supported also by analysis of /Z  experimental /Z reproduced with γ=14 MeV SMM calculation for γ=4,8,14,25 MeV and 136 Xe, 124 Xe E*/A=4 MeV by A.Botvina Z=10-13

Summary  isotopic identification in the complete Z range was obtained for residues from 136 Xe (N/Z=1.52) and 124 Xe (N/Z=1.30) projectiles  final /Z reveal a sensitivity to the length of an evaporation cascade  isoscaling was observed in broad Z range Universal freeze-out temperature deduced in the broad Z range: From isotopes with Z=10-13 the symmetry coefficient γ=11-14 MeV was extracted Comparison with SMM calculation and /Z of data supports decrease of symmetry coefficient for hot fragments T f ~5MeV for 136 Xe T f ~4MeV for 124 Xe