engleski

Rapid method for simultaneous measurements of total alpha, 222Rn and 220Rn activity in soil gas.

The rapid method for simultaneous measurement of the total alpha, radon (222Rn) and thoron (220Rn) activity in soil gas is based on the fact that 220Rn had very short half-life of 55.6 s in comparison to 222Rn with 91.8 h. Measuring equipment is consisting of Alpha Guard Professional Radon Monitor (AGRM), air pump with soil gas measuring probe, polyethylene bag, few tubes and filters. There are two measuring steps. In the first step, air pump brings soil gas into AGRM and the total alpha activity in soil gas is measured in flow rate mode. Meanwhile, on the outlet of AGRM ionisation chamber, measured air is collected and stored into adequate polyethylene bag of appropriate volume. After five to ten one-minute repeated measurements in this mode, one pause of few minutes follows. In the second step, air pump brings soil gas, collected and stored during the first measuring step, from polyethylene bag once again into AGRM. Results collected in the first measuring step present the total alpha activity in soil gas, while results from the second step present 222Rn activity in soil gas. The difference between first and second measurements gives 220Rn activity in soil gas. Depending on flow rate of soil gas controlled by air pump, observed 220Rn activities need to be recalculated for the decay correction factors. Radon and thoron in soil gas are the products of theirs parent radionuclides decay and, consequently, theirs activities measured in soil gas are function of parent radionuclides concentration, emanation from a soil particles, soil porosity and inter-pores soil air communication ability. High 220Rn activities in soil gas are the result of 224Ra decay in the surrounding of measured point, indicating high emanation potential and high degree of inter-pores soil air communication ability. Absence or very low 220Rn activity indicates that 222Rn present in soil gas is the result of its migration from greater distances, not the consequence of 226Ra decay and 222Rn emanation from soil in the surrounding of measured point only.

Radon and thoron measurement; soil gas; rapid method;

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