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 dose s from I x 10(5) Gy (10 Mrad) up to 1.2 x 10(6) Gy (120 Mrad) at an increme ntal dose of I x 10(5) Gy (10 Mrad). The gamma source was a 9.03 PBq (244 k Ci) 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 met hods: 1-thickness change method; 2-mass change method; 3-fission track diam etric method. The study gives a comparison and limitations of these three m ethods 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 t he 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 e tch rate decreases exponentially with the etching time at a fixed gamma abs orbed dose in all three methods. The thickness change and mass change metho ds have successfully been applied to measure V-b at higher gamma doses up t o 1.2 x 10(6) Gy (120 Mrad). The bulk etch rate determined by the mass chan ge 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 meth od it was not possible to measure the fission fragment track diameters at h igher doses due to the quick disappearance of the fission tracks and theref ore the V-b could not be estimated at higher gamma doses. (C) 2001 Elsevier Science Ltd. All rights reserved.