2.3. Radiometric analysis
Each soil sample was placed directly on the detector and counted for 48 h. The activity associated with a Marinelli beaker filled with inactive deionised water was also measured in order to determine the background level in the environment around the detector. Equal counting times for background and sample measurements were used. Spectrum analysis and nuclide identification were performed via the Genie 2000 software. As listed in Table 1, a range of gamma-ray transitions from a number of the decay chain members of the 238U and 232Th primordial decay chains were utilised in order to obtain consistent values for the activity concentrations of these nuclei and their decay daughters. The activity concentration values quoted assume secular equilibrium for the different isotopic activities in the decay chains. In order to indicate the assumption of equilibrium through the decay chains, activity ratios between parent/daughter and/or between daughter and daughter nuclide were also investigated [14]. The activity concentrations of 40K and 137Cs were determined directly by measurement of the gamma-ray transitions at 1460.8 and 661.6 keV, respectively. The net counts under each photopeak of interest were used to calculate the activity concentration of particular radionuclides in the soil samples. The activity concentration in soil samples was given by the following equation [15], [16], [17] and [18]:
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