Determination of track etch rates from wall profiles of particle tracks etched in direct and reversed direction in PADC CR-39 SSNTDs

Abstract

Commonly track etch rates are determined by 2-dimensional images of track opening (diameter) or track length measurements in dependence on etching time. Whereas the track diameter method yields reliable results in the case of conical track profiles only, the track length method is widely applied to obtain variable track etch rates along the particle trajectory. The development of a more refined microscopic technique, the con-focal scanning microscopy (CSM), the recording of 3-dimensional images of tracks has been realised. Furthermore, using monochromatic laser and fluorescent light the spatial resolution has been also improved. By a sophisticated software the co-ordinates of the track wall can be reconstructed automatically at any point of the track length. From these data the track etch rate can be recalculated along the whole track from only one 3D-image. Using this technique, the present paper describes the investigation of the track evolution by etching in direct and reversed (i.e. etching against the particle incidence) direction. The knowledge of the track formation process in reversed direction is important for calculation of tracks from secondary charged particles emitted in backward directions by interaction of neutrons with atoms of the detector material. To demonstrate this powerful method, tracks of 4He and 7Li-ions have been evaluated with following results: - the investigation of the etching process in reversed direction yields valuable information for the track etch rate behind the Bragg peak (i.e. the so-called thin-down-region) - the track etch rates obtained from direct and reversed etching are identical within the experimental uncertainty - all data can be represented by their dependence on the residual range