A CFD-based approach to optimize operating parameters of a flow-through scintillation cell for measurement of 220Rn in indoor environments

The measurements and monitoring of ²²²Rn/²²⁰Rn have been of emerging interest in occupational environments particularly in radium/thorium handling facilities and environments with monazite deposits for the inhalation dosimetry. The performance of a flow-through Lucas scintillation cell (LSC) for long run ²²⁰Rn measurements, depends upon the exact distribution pattern of ²²⁰Rn and its decay products in the LSC which can vary with the design of inlet path and flow rates. In this work, the CFD technique has been used to study the concentration profiles of ²²⁰Rn and its decay products in LSC for varying flow rates and inlet needle lengths. The variation of alpha production efficiency (η_α) is computed and analyzed for each case; aiming to select the best operating range of parameters for the optimum performance of LSC for ²²⁰Rn measurements. It is seen that LSC can be operated in the flow rate ranging from 0.6 to 1 lpm with inlet needle length varying from 22.5 to 45 mm for improved sensitivity.

Numerical simulation of 222Rn profiling in an experimental chamber using CFD technique

Measurement of indoor ²²²Rn concentration and interpretation of distribution patterns are important for inhalation dosimetry in occupational and residential areas. Experimental determination of ²²²Rn concentration distribution and estimation of inhalation doses depend on the underlying aspects such as calibration of the detectors, accuracy of the techniques etc. Therefore, ²²²Rn concentration distribution needs to be very well understood in a closed domain for the controlled studies. In the recent times, Computational fluid dynamics (CFD) technique has gained a lot of attention for the prediction and visualization of indoor ²²²Rn concentration profiles and their mixing ability in the domain. The present study aims to simulate the effect of forced mixing on the ²²²Rn concentration profile in a 22 m³ experimental chamber. This chamber is designed for carrying out the controlled experiments, calibration and inter-comparison studies of various types of ²²²Rn detectors. Effect of different parameters such as time, flow rates, fan-off and fan-on conditions have been studied on the transient response, extent of the air mixing patterns and subsequently on ²²²Rn concentration profile in the chamber. Further, Non uniformity index (NUI) is introduced as a measure of the uniformity of the distribution in the closed domain. NUI is estimated for different cases in order to efficiently interpret the effect of above mentioned parameters on ²²²Rn profile in the chamber. This study will be useful to represent the turbulent conditions in real indoor domains and occupational facilities as U-mines during calibration and inter-comparison exercises of different ²²²Rn detectors.