Assignment of particle tracks to spores of Bacillus subtilis on silver chloride detectors.

In Biostack III B, flown in the Apollo-Soyuz Test Project, AgCl detectors were used to study ionizing effects of HZE particles on spores of Bacillus subtilis or eggs of Artemia salina. The tracks of these particles inside the detectors are used to extrapolate the path of the particle near the biological objects which are fixed at the detector surface. The closest distance to the geometric centre of the object, the so-called impact parameter, is determined with a mean accuracy of 0.3 micrometers for 1 micrometers spores. From knowledge of the lateral distribution of the energy transferred by primary and secondary ionization effects of the particle, the energy deposit and its localization at the objects can be determined. We describe some technical aspects of a video-electronic scanning system, Quantimet 720, which has been adjusted to the particular requirements of these experiments. The main improvements achieved are increased precision of coordinate measurements, objective focusing of the microscopic image combined with measurements of the density profile of particle tracks, and finally speeding up of the measurements by automatic data transfer.