Track Formation in Plastics

It is proposed that the “threshold for etchable track formation” in plastics is associated with the linear density of activated polymeric clusters along the path of an ion, in the “grain-count regime.” Existing data for CR-39 reveal a change in etching rate in the neighborhood of z/β having the value of about 15-20. We infer that this defines the transition from the grain count regime to the track width regime, as the activation cross-section exceeds the cross-sectional area of the cluster. This interpretation is consistent with available data for the G value for polymer scission and the dose of gamma-rays required for enhanced etching of the bulk material. CR-39 appears to be a 1-hit detector. A similar track theory interpretation appears to be consistent with observed changes in bulk etching of photoresists irradiated with electrons and heavy ions of different LET.