Einfluss der Umladung beim Abbremsen von Schwerionen im Energiebereich (100 - 1000) MeV/u
Abstract
The influence of charge exchange on the slowing down of heavy ions in the energy range (100 - 1000) MeV/u
In this thesis the energy loss and charge exchange of relativistic gold,
lead, and bismuth ions in matter was studied in the range from
100 MeV/u to 1000 MeV/u.
The investigations were performed using the magnetic spectrometer FRS at GSI.
In several experimental runs the atomic charge-changing cross sections,
equilibrium charge state distributions, stopping-power values,
and energy-loss straggling in solids were measured.
For this purpose the FRS was operated in different ion-optical modes
and the atomic interactions were investigated in
various materials ranging from beryllium to lead (Z = 4 - 82).
One main goal was to precisely determine the charge dependence of the
stopping power. As it could be shown for the first time, a model based on the
accurate knowledge of the charge state distribution in combination with the
LS theory [1].
can describe the stopping power within an accuracy of
1% [2].
Thus the energy loss is on a solid basis and the charge-changing cross
sections are known sufficiently well from theory and the conducted
experiments.
Therefore, it was possible for the first time to distinguish precisely
between the contributions from charge-exchange straggling and collisional
straggling to the variation of the energy loss. As a result we found a
drastic enhancement due to charge-exchange straggling in target materials
with low atomic number [3].
The experimental results on charge-exchange straggling could also be confirmed
by a simulation program. In addition these calculations allow to draw
a conclusion on the role of incomplete screening of the projectile in
close collisions.
Such investigations offer a new approach for heavy ions since with
charge-exchange straggling one can measure directly the differences in the
partial stopping powers. In this way the analysis opens the path for a
necessary expansion of the LS theory.
The accuracy of the measurements even allows to study the third statistical
moment of the energy-loss distribution.
The skewness due to charge-exchange straggling is caused by the
large free path length in the energy and target domain investigated and
was also observed for the first time.
The new results on the atomic interaction of relativistic heavy ions
from this thesis have a direct application in separating exotic nuclei
produced by fragmentation or fission in flight.
As has been shown in this thesis, the resolution of a separator operating by
the B
- 
E - B
method is mainly governed by the variation of the energy loss in matter.
The energy-loss straggling also determines the range distribution of stopped
fragments. A combination of dispersive spectrometer stages with shaped
degraders allows a range bunching. Therefore, this will be essential
for new developments on the field of experiments with exotic nuclear beams.
For instance, these new applications will be part of the new facilities in
the USA (RIA), Japan (RIKEN) and at GSI (SUPER-FRS).
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Kontakt: geb@bibsys.uni-giessen.de, 11.03.2003
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