Behavior of radon progeny produced in a scintillation cell in the flow-through condition

• A numerical model was made to analyze alpha counts with a flow-through scintillation cell.
• Detection efficiencies were compared between the static and flow-through cells.
• An empirical formula of 218Po deposition on the cell wall was obtained as a function of flow rate.
• This study is helpful to not only radon but also thoron measurements using the flow-through cell.

When a scintillation cell is used for radon measurement, detection efficiencies for individual alpha emitters (222Rn, 218Po and 214Po) are required depending on the methods of data analysis. To estimate their detection efficiencies, Monte Carlo simulation has been implemented to track alpha particles emitted in the cell in the static condition. However, such an effort has not been made for the flow-through condition. The present study describes an attempt to obtain an empirical parameter which is necessary to predict the behavior of radon progeny in the flow-through cell: the fraction of the progeny generated in the cell which is deposited onto the wall. As a result, it was found that the deposition fraction of 218Po decreases exponentially with increasing flow rate in the range of 0.25–2 l min−1. An empirical formula was acquired to estimate the deposition fraction of 218Po as a function of flow rate. This result is helpful in understanding the characteristics of the scintillation cell. The empirical formula derived in this study can also be applied to predicting the behavior of thoron progeny (212Pb and its progeny) in continuous thoron measurements with the flow-through scintillation cell.