Track Structure Studies
 Motivation
 Method
 Results
 Publications
 Documentations

Motivation
The main goal of track structure studies is to understand radiation
action and radiation damage, especially of heavy ions,
on the microscopic level, i.e. on
a micrometer or even nanometer level.
This is in particular important for radiation damage in biological
systems. The most sensitive structures are the two DNA strands
separated by only a few nanometers.
In addition, also radiation transport in nonbiological systems
like dosimeters, ionization chambers and thin foils can be
described on a microscopic level by taking into account each single
interaction of a charged particle with an atom or molecule of the
target material.
Calculational Method
The problem of radiation transport on the single interaction level
is most conveniently handled by Monte Carlo (MC) methods. This allows
to model the stochastic nature of the radiation action.
The most important inputs for such calculations
are:

the primary cross sections (double differential,
in angle and energy) for deltaelectron
creation (as obtained e.g. by the Binary Encounter Approximation)
 semiempirical
cross sections (for elastic scattering, ionization and excitation)
of lowenergy electrons to handle the
diffusion and slowing down of
electrons once they are created by a heavy ion.
Results
At first,
the Monte Carlo calculations allow to illustrate the paths of heavy ions
and their deltaelectrons traversing matter
(click on the picture to enlarge it):
,
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Dose distributions as a function of the radial distance from the ion path are
more quantitative results which allow comparison with experiments.
The figure shows experimental data (symbols) measured in gas and scaled to
liquid water density together with MC results (green histogram).
The agreement is very good. In addition the results from calculations
according to the Katz and the Chatterjee model are shown too.
All models show good agreement with each other as well as with the experiment
at medium distances. Here the dose falls off like 1/r**2.
At very small and very large distances, however, the MC results are closer
to experiment.
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A real advantage of Monte Carlo techniques is the possibility to obtain
eventbyevent correlations. Therefore average "event sizes",
i.e. the mean dose deposition in small volumes can be determined.
The picture below shows measurements (symbols, Toburen et al)
as well as calculations (curve)
for small volumes corresponding to 0.5 micrometer diameter in
liquid water. The long range tail due to deltaelectron events can clearly
be seen in experiment as well as in the simulation.
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GIF
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Publications

M.Krämer, G.Kraft:
Calculations of heavyion track structure
Radiat Environ Biophys (1994) 33:91109

M.Krämer, G. Kraft:
Track structure and DNA damage
Adv. Space Res. Vol 14. No.10. pp(10)151(10)159,1994

G.Kraft, M.Krämer:
Linear Energy Transfer and Track Structure
in: Advances in Radiation Biology, Vol. 17, 1993

G.Kraft, M.Krämer, M.Scholz:
LET, track structure, and models.
Radiat Environ Biophys (1992) 31:161180
Documentations
A description of the computer code is
here
Last update: April 5th, 2001, M.Kraemer@gsi.de