Objective:To demonstrate the versatility of the natural soil gas harvesting technique,coupled with a semi-dynamic injection algorithm,as an efficient and reliable source for continuous ^(222)Rn delivery to a large-vol...Objective:To demonstrate the versatility of the natural soil gas harvesting technique,coupled with a semi-dynamic injection algorithm,as an efficient and reliable source for continuous ^(222)Rn delivery to a large-volume calibration chamber across different soil conditions and climatic conditions.Methods:Long-term experiments were performed during three seasons of a year in a tropical monsoonal climatic region with high rainfall on the Southwest Coast of India.Soil gas extraction was performed using soil-gas probes,inserted to 1 m deep into the ground.Soil gas was harvested at a flow rate of 60 L/min,passed through a moisture trap,a ^(222)Rn progeny filter,and a delay volume and pumped into a ^(222)Rn calibration chamber of volume 22.7 m^(3).Continuous monitoring of ^(222)Rn concentration in the chamber was performed using ionization chamber-based reference monitors.To achieve and maintain the desired ^(222)Rn concentration values in the calibration chamber,the semi-dynamic injection method was adopted,in which the ^(222)Rn concentration in the soil gas was monitored periodically,and injection into the chamber was controlled using a well-defined pumping algorithm.Three ranges of ^(222)Rn concentration values were chosen as the target values to be maintained in the calibration chamber for long-term experiments(15 d):low concentration(500-1,000 Bq/m3),medium concentration(1,000-10,000 Bq/m^(3)),and high concentration(10,000-25,000 Bq/m^(3)).Results:The achieved ^(222)Rn concentration values were in good agreement with the target values,with deviations of 12%,8% and 5% for the low,medium and high concentration exposures,respectively,during the summer season.During the monsoon season,the deviations between the target and the achieved concentration values were 12%,10% and 5% for low,medium and high concentration exposures,respectively,and the corresponding deviations were 12%,4%,and 5% for the winter season.These deviations are well within the cumulative uncertainty associated with the measurements.Conclusions:The results of this study conclusively demonstrate that the soil gas harvesting method,when coupled with the semi-dynamic injection approach,is a reliable method for generating and maintaining the desired ^(222)Rn concentration in the large volume calibration chamber during different seasons and environmental conditions.展开更多
文摘Objective:To demonstrate the versatility of the natural soil gas harvesting technique,coupled with a semi-dynamic injection algorithm,as an efficient and reliable source for continuous ^(222)Rn delivery to a large-volume calibration chamber across different soil conditions and climatic conditions.Methods:Long-term experiments were performed during three seasons of a year in a tropical monsoonal climatic region with high rainfall on the Southwest Coast of India.Soil gas extraction was performed using soil-gas probes,inserted to 1 m deep into the ground.Soil gas was harvested at a flow rate of 60 L/min,passed through a moisture trap,a ^(222)Rn progeny filter,and a delay volume and pumped into a ^(222)Rn calibration chamber of volume 22.7 m^(3).Continuous monitoring of ^(222)Rn concentration in the chamber was performed using ionization chamber-based reference monitors.To achieve and maintain the desired ^(222)Rn concentration values in the calibration chamber,the semi-dynamic injection method was adopted,in which the ^(222)Rn concentration in the soil gas was monitored periodically,and injection into the chamber was controlled using a well-defined pumping algorithm.Three ranges of ^(222)Rn concentration values were chosen as the target values to be maintained in the calibration chamber for long-term experiments(15 d):low concentration(500-1,000 Bq/m3),medium concentration(1,000-10,000 Bq/m^(3)),and high concentration(10,000-25,000 Bq/m^(3)).Results:The achieved ^(222)Rn concentration values were in good agreement with the target values,with deviations of 12%,8% and 5% for the low,medium and high concentration exposures,respectively,during the summer season.During the monsoon season,the deviations between the target and the achieved concentration values were 12%,10% and 5% for low,medium and high concentration exposures,respectively,and the corresponding deviations were 12%,4%,and 5% for the winter season.These deviations are well within the cumulative uncertainty associated with the measurements.Conclusions:The results of this study conclusively demonstrate that the soil gas harvesting method,when coupled with the semi-dynamic injection approach,is a reliable method for generating and maintaining the desired ^(222)Rn concentration in the large volume calibration chamber during different seasons and environmental conditions.
