Track Structure Studies
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 non-biological 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
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
the primary cross sections (double differential,
in angle and energy) for delta-electron
creation (as obtained e.g. by the Binary Encounter Approximation)
cross sections (for elastic scattering, ionization and excitation)
of low-energy electrons to handle the
diffusion and slowing down of
electrons once they are created by a heavy ion.
the Monte Carlo calculations allow to illustrate the paths of heavy ions
and their delta-electrons traversing matter
(click on the picture to enlarge it):
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
A real advantage of Monte Carlo techniques is the possibility to obtain
event-by-event 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 delta-electron events can clearly
be seen in experiment as well as in the simulation.
Calculations of heavy-ion track structure
Radiat Environ Biophys (1994) 33:91-109
M.Krämer, G. Kraft:
Track structure and DNA damage
Adv. Space Res. Vol 14. No.10. pp(10)151-(10)159,1994
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) 31:161-180
A description of the computer code is
Last update: April 5th, 2001, M.Kraemer@gsi.de