Etched track profiles for relativistic 7 GeV silicon and 17.48 GeV Nickel ions in PADC detector: The case study of convex track walls

650 mu m thick PADC foils are exposed to 7 GeV Silicon and 17.48 GeV Nickel accelerated ions at particle fluence of about 1000 cm-2. The relativistic ions passed through the entire thickness of the PADC foils and created latent tracks that were etched sequentially under strong etching conditions (NaOH + ethanol). For each time sequence, etched track profiles were found by carefully polishing the detector edge, and then imaged in order to measure their geometrical parameters (diameter and length). Track wall curvature study allows for better understanding of the physico-chemical interactions undertaken during the etching process. Etched track profiles have the distinctive feature of presenting concave walls near to the track aperture. Such special feature is likely to be due to a depth dependent variation of the bulk etch rate (Vb). This depth dependence is investigated and discussed. A simulation program has been written based on the variational principle, it uses experimentally determined variable Vb and a constant specific track etch rate (Vt). Simulations results are in good agreement with experimental micrographs both qualitatively and quantitatively. Such case study may show promise as a means of fabricating controlled shape pores in polymer membranes.