Interpretation of Mason's equation in terms of measurable electrochemical-etching parameters governing the dielectric breakdown phenomenon

Abstract

A new interpretation of Mason's (1959) equation, as applicable to the electrochemical etching (ECE) of tracks in polymers, is presented in terms of physically meaningful track-etching parameters. The values of these parameters have been experimentally obtained by irradiating CR-39 foils with heavy ions (238U and 129Xe) and α-particles of various energies, and applying chemical pre-etching (CPE), followed by ECE in steps, with increasing electric field until the ‘treeing’ breakdown is initiated. A value of 1.19 MV cm-1 is obtained for the intrinsic electrical breakdown stress of CR-39. It is found that the track radius r used in Mason's equation is related to the radius rϑ of a sphere, inscribed within the etch cone, whose lowest point is at a fixed distance l0 above the cone tip, with lo ⋍ 1.75 μm for α-particle tracks of energies 2–5.5 MeV, such that r= 0.43 + rϑ (in μm).