Determination of CR-39 and LR-115 Type II Mean Critical Angle of Etching Using a New Monte Carlo Code

摘要

CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs) are used, in order to assess the concentration of nuclides belonging to U-238 and Th-232 series, and these ones can be also used to measure the contents of radon Rn-222 and thoron Rn-220 gases in different locations. In this paper, a Monte Carlo code was developed to calculate the mean critical angle for which alpha particles emitted from U-238 and Th-232 families in studied material samples reach CR-39 and LR-115 type II surfaces and bring about latent tracks on them. The dependence of the SSNTDs mean critical angle on the removed thickness and the initial alpha particle energy has been studied. A linear relationship between CR-39 mean critical angle and the initial alpha particle energy for different removed thicknesses has been found. This straightforward relationship allows determining quickly the mean critical angle of etching which corresponds to initial alpha particle energy for a given removed thickness. CR-39 mean critical angle ranged from 59 deg for an alpha particle emitted by Po-212 to 71 deg for an alpha particle emitted by Th-232, for the value of removed thickness of 6 mu m; whereas LR-115 type 11 mean critical angle does not depend on the initial alpha particle energy except for Th-232, U-238, Th-230, and Ra-234 when the removed thickness ranged from 6 mu m to 8 mu m. Obtained data by using the current method and those obtained in the literature are in good agreement with each other.