Detailed gamma-ray spectrometric analysis of natural radionuclides of K, U, and Th on the Sudetic Marginal Fault
Abstract
Concentrations of natural radionuclides of K, U and Th along vertical profile of a research trench studying the Sudetic Marginal Fault were established by detailed focused gamma-ray spectrometric measurements. Analyses of K, U, Th were carried out by two gamma-ray spectrometers, i.e.
GS-256 and newly introduced GT-40S (Georadis). The GS-256 is a portable gamma-ray spectrometer of standard design, which was calibrated at calibration facility Stráž pod Ralskem, Czech Republic.
Focusing of GS-256 detector was achieved by placing the probe in a ring-shaped lead shield. Since the lead shielding is changing instrument's response to gamma-rays and its calibration constants, it is necessary to apply shielding correction factors when determining K, U and Th (Table 1).
The gamma-ray spectrometer GT-40S is specially designed for focused measurements. The lead shielding (thickness 25 mm, inner diameter 70 mm, weight 9 kg) is built into the probe.
The GT-40S was calibrated using Grasty's transportable calibration pads. The abnormality of the obtained radiometric data was statistically treated and tested using the range of +-3S (standard deviation) of the mean.
The test has shown thorium anomaly to be bound to rocks of the fault zone, while concentrations of potassium and uranium have not indicated any significant change or affinity (Table 2, Fig. 2). Statistical identity of the results obtained by using the GS-256 and GT-40S instruments was tested by Student's t-test for paired samples based on a hypothesis that the results of measurements using two instruments are statistically not different.
The test parameters are shown in Table 3. Potassium and uranium analyzed by the two instruments show small deviations close to magnitude of measurements errors.
Concentrations of thorium established by the two gamma-ray spectrometers were found to be statistically identical.