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The principal aim of the present study is to improve the empirical basis for radioactivity measurements by using two different methods and deduce the optimum conditions that should be applied.
The above aim has been achieved as the following:
Check out the detector system which will be used to measure radon activities by alpha sensitive (CR-39) plastic track detectors. CR-39 detectors were tested for recording alpha tracks with different spaces between the detector and the source which will be irradiated by reference standard source (Am-241). Alpha track shapes have been outlined and track diameters and densities have been registered for different detectors to source spacing. Obtained results have been analyzed to construct empirical relation yield the dependence of the alpha track diameters on detector to source spacing. The results showed that alpha track diameter has been increased as the detector to source spacing increased, also the maximum diameter ranges between 7.26 and 17.96m. It is noticed that the alpha tracks has been stopped for alpha source detector spacing larger than 40 mm, which is equivalent to alpha range in air. Results have been compared by the produced alpha tracks due to Rn-222 occurred as Ra-226 alpha decay from twenty natural samples selected from Sinai- Egypt, to estimate the heights at which the radon was decayed.
Results indicated that, there is effective zone of the chamber located from 10 ~ 56mm of the radon chamber, where only radon atoms do its alpha decay within this zone will recorded by the CR-39 detector.
This zone, logically, was depended on the sample activity where radon molecules bunched with each other.
Determination of radionuclides distribution and radon activities have been carried out, by means of gamma spectrometry using Hyper Pure Germanium detector (HPGe) and alpha particles tracks measurements using SSNTD (CR-39), in the same above studied twenty samples. The results of the present study were discussed and compared with internationally recommended values. Calculations of environmental hazards for the studied area have been took place. The mean activity concentration of the radionuclides in different samples is presented and indicates that 238U concentration was significant in all measured samples and far from recommended value. Results referred to all these localities show that 238U and 226Ra activities were in disequilibrium where activity ratio of 238U /226Ra ranges from 0.52 to 4.66. Abundance ratio of Th /U ranges from 0.01 to1.46 which is far from natural ratio; this indicates that there is adding of uranium to the studied rocks. Measured 40K activities show that all samples were less than recommended value except samples 13, 15, 16 and 19.
Also it was found that the maximum radon concentration present at sample 11 (333296). Radon exhalation rate was calculated using α-track detector, with average equal to 0.27 (Bq m-2 h-1). Also emanation coefficient has been calculated for all studied samples by considering that radon and radium in secular equilibrium, i.e. activity of true occurred radon equal to activity of obtained radium from gamma measurements.
The total gamma mean absorbed dose rates due to the presence of 232Th, 238U and 40K in these samples in different locations varied between 14.31 and 17489.2 nGyh-1. These values correspond to an annual effective dose equivalent of 0.02-21.45 mSvy-1.