{ 57 { Study of DNA{Damage Structure along the Tracks of Energetic Ions

The cell irradiation setup at the scanning ion microprobe SNAKE is routinely used for biological microirradiation ex-periments [1]. In these experiments, DNA{repair factors accumulating at sites of radiation{induced DNA double{ strand breaks are visualized using immuno uorescence techniques [2]. In 2005 new studies concerning the damage structure in cell nuclei along the tracks of single ions were started [3]. In order to obtain a high optical resolution along the track di-rection during uorescence microscopy it is advantageous to perform the irradiation with a beam direction that is almost parallel to the cell carrier substrate [4,5]. There-fore HeLa{cells were irradiated at the irradiation setup of SNAKE in a modied geometry (see gure 1). ion beam vacuum atmosphere ring-shaped cell container cell carrier foil living cells beam exit nozzle culture medium 10° max. 24 mm Fig. 1: Modied irradiation geometry: ion beam direction and cell carrier foil enclose an angle of 10. Due to the distance of several tens of millimeters be-tween exit window and cells it is not possible to perform the irradiation with microscopic resolution. Furthermore, with this setup it is not possible to detect the ions that have transversed the cell sample. Thus, the particle uence dur-ing irradiation was chosen to ascertain that in many cell nuclei single ion trajectories could be expected. In gure 2 and 3 examples of HeLa{cell nuclei irradiated under the described geometry with each one particle are shown. 15 µ