Many-hit model calculations for track etch rate in CR-39 SSNTD using confocal microscope data

Abstract

The present work studied an important part of ion tracks: the Bragg peak region. Information about the microscopic nature of ion-energy dissipation based on zero-approximation in frame of the many-hit model of the track structure theory was studied. The detector response, Vt, was calculated in terms of Poisson’s distribution as a function of the ion’s linear energy transfer (LET). This approach can be considered to be a zero-approximation since LET is a special case of restricted energy losses with a cut off energy wcutoff=∞: LET=REL∞. Confocal microscopic data allows the visualising and analysing of the etched tracks one by one with high precision. A three-dimensional track image was observed and the track etch rate was measured. On the basis of χ2 analysis of the experimental track etch rate (square of the least deviation), with respect to that of the theoretical value, information about the energy transfer process can be obtained. Light ions of little MeV energy were slowed down in the CR-39 detector and the detectors responses close to the Bragg peak region were studied. It was shown that in the zero-approximation no one to one relation can be found between the primary linear energy transfer (LET) and the measured specific track etch rate. The statistical analysis can be split into two separate parts; before the Bragg peak (Bethe–Bloch) and after the Bragg peak (Thin Down). The two parts analysed reflect the separated domains where the etching rate increases or decreases, due to the different role of the delta-electrons in each of these domains. The main aim of this study is to develop a method for any ion describing Vt in this very sensitive Bragg region. This would allow ion identification at low velocities on the one hand, and on the other hand to have a better understanding of the physical processes involved during high velocity ion stopping.