Comparison and limitations of three different bulk etch rate measurement methods used for gamma irradiated pm-355 detectors

Samples of Nuclear Track Detectors (PM-355) were exposed to high gamma doses from 1 × 10⁵ Gy (10 Mrad) up to 1.2 × 10⁶ Gy (120 Mrad) at an incremental dose of 1 × 10⁵ Gy (10 Mrad). The gamma source was a 9.03 PBq (244 kCi) Co-60 source used for sterilization of medical syringes. The bulk etch rate (V_b) was measured for various high gamma doses by three different methods: 1-thickness change method; 2-mass change method; 3-fission track diametric method. The study gives a comparison and limitations of these three methods used for bulk etch rate measurements in the detectors as a function of high gamma doses. The track etch rate (V_t) and the sensitivity (V) of the detector were also measured using the fission track diametric method. It was observed that V_b increases with the increase of the gamma absorbed dose at a fixed etching time in each bulk etch measuring method. The bulk etch rate decreases exponentially with the etching time at a fixed gamma absorbed dose in all three methods. The thickness change and mass change methods have successfully been applied to measure V_b at higher gamma doses up to 1.2 × 10⁶ Gy (120 Mrad). The bulk etch rate determined by the mass change and thickness change methods was almost the same at a certain gamma dose and etching time whereas it was quite low in the case of the fission track diametric method due to its limitations at higher doses. Also in this method it was not possible to measure the fission fragment track diameters at higher doses due to the quick disappearance of the fission tracks and therefore the V_b could not be estimated at higher gamma doses.