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

2. 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

3. 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

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

5. <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

6. 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

7. 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

8. 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