GSI-Darmstadt, Germany Isotopic composition of residues produced in the fragmentation of 124Xe and 136Xe projectiles Daniela Henzlova NSCL-MSU, Michigan GSI-Darmstadt, Germany

Motivation isotopically resolved final residues allow to investigate the properties of highly excited nuclear system formed in heavy-ion collisions experiments 124Xe(N/Z=1.30)+Pb, 136Xe(N/Z=1.52)+Pb at 1AGeV at the FRS: high isotopic resolution investigations extended over a full range of the nuclear charge relativistic energy regime influence of dynamics and isospin diffusion largely reduced main interests: influence of the evaporation process and nuclear break-up on the final isotopic composition

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

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

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

Influence of the cluster emission according to R.J.Charity, Phys. Rev. C 58 (1998), 1073 cluster emission may prevent reaching corridor for asymmetric systems ABRABLA – abrasion+evaporation code n, p, alpha emission -> too strong removal of memory on initial N/Z implementation of cluster emission (d, t, 3He, IMF (Z>2)) memory on initial N/Z restored not sufficient to reproduce <N>/Z of experimental data

Influence of the thermal conditions at the freeze-out of the break-up break-up abrasion E*=aT2 evaporation <N>/Z of residues from 124Xe less sensitive to length of evaporation cascade only introduction of nuclear break-up allows reproduction of experimental data final <N>/Z sensitive to thermal conditions at the freeze-out Tf=5-6 MeV and 3-4 MeV for 136Xe and 124Xe, respectively

Conclusions isotopically resolved residues in the broad Z range were measured in fragmentation of 136Xe (N/Z=1.52) and 124Xe (N/Z=1.30) projectiles comparison with ABRABLA suggests that evaporation of complex clusters is not sufficient to explain high <N>/Z of the experimental data may be reproduced only upon introducing nuclear break-up final <N>/Z reveal sensitivity to the length of an evaporation cascade following the nuclear break-up Tf ~ 5-6 MeV for 136Xe Tf ~ 3-4 MeV for 124Xe BUT: Careful description of the reaction process needed to draw the quantitative conclusion