For the first time, etched track diameter and over-etched track diameter (OETD) measurements have been used to determine etchable track lengths in thermally treated poly allyl diglycole carbonate (PADC) in the form of CR-39, as well as heavy ion track ranges in non-thermally treated samples. These heavy ions are produced spontaneously from 252Cf radioactive source as fission fragments. Isochronal heating experiment was conducted on CR-39 detectors prior to their irradiation to 252Cf radioactive source. In a reverse sequence, another set of detector films was first subjected to 252Cf irradiation and then thermally treated as described above. The diameters of etched heavy ion tracks in non-thermally treated and thermally treated CR-39 detectors have been measured as a function of etching time at different heating temperatures and times. The fission fragment ranges in non- thermally treated CR-39 detectors determined using the OETD method were found to be 17.7 ± 0.2 μm for the heavy group and 21.8 ± 0.3 μm for the light group, whereas the etchable track lengths in thermally treated detectors are by far lesser than that those of non-thermally treated ones. The results of heavy ion ranges in non- thermally treated detectors are in excellent agreement with theoretical calculations based on SRIM code. While in the case of the etchable track lengths of these heavy ions in thermally treated detectors, there is no such theoretical data for comparison with experiment till present.