Radon progeny concentrations measurement in tunnel by in-situ HPGe γ spectrometry

The method was studied to determine the radon progeny Concentrations in tunnel by in-situ HPGe γ spectrometry. The characteristic γ rays of ²¹⁴Pb (²¹⁴Bi) in tunnel could be detected by in-situ HPGe γ spectrometry directly, but the contributions for count rates were from air and rocks in tunnel, respectively. The systems of equations composed of count rates, efficiency factors and activity concentrations of ²¹⁴Pb (²¹⁴Bi) in the air and rocks were constructed. The system of equations were solved by the expectation maximization algorithm (EM) to obtain the activity concentrations of ²¹⁴Pb (²¹⁴Bi) in the air. Although ²¹⁸Po wasn't able to be measured by in-situ HPGe detector directly, its concentration could be calculated on the basis of ²¹⁴Pb. An experiment had been performed for 24 hours in a perennial closed tunnel, and 8 γ-spectrums were obtained. The concentrations of ²¹⁴Pb and ²¹⁴Bi in the air were calculated respectively. Then the concentrations of ²¹⁸Po were calculated in accordance with the concentrations of ²¹⁴Pb and ²¹⁴Bi. And this method was feasible by verification the results. (authors)