An alternative method for counting tracks in solid state nuclear tracks detectors

Solid State Nuclear Tracks Detectors (SSNTD) are organic plastic materials capable to register radiation damages (the so-called latent track of ∼50-100 angstrom) caused by heavily ionizing charged particles like alpha particles, protons and fission fragments. After exposure to radiation, the detectors are placed in a chemical etching solution, so the trail of the nuclear particle becomes visible under an optical microscope. The major difficulty is the reading and the quantification of the tracks. The tracks can be read manually under a microscope or using electrical discharge. Also, several researchers are using automatic counting systems, but when dealing with high tracks densities, the problem is complex and not simply to solve. In this work, in order to simplify manual reading of Solid State Nuclear Tracks Detectors (SSNTD) submitted to high radon and thoron concentrations, we present a 'tracks reading factor', FT, related with the density and distribution of the tracks. The procedure assumes that the tracks are uniformly distributed over the entire 1 cm2 surface area of the detector and allows the counting of only few central stripes. For the assessment of radon concentrations in caves, we obtained a FT factor of 91.55 ±6.67, determined as the rate of total mean tracks density to the mean tracks density of 3 central stripes for 5 track Makrofol E detectors. The detector tracks density is now obtained by multiplying the mean value of 3 central stripes by the FT factor, instead of reading all the detector area. The procedure was validated by irradiating a set of 5 track detectors under a well-known 222Rn concentration and calculating the source activity by using our FT factor. The result shows a normalized deviation of - 0.7 from the 'true value'. (author)