An innovative technique of harvesting soil gas as a highly efficient source of 222 Rn for calibration applications in a walk-in type chamber: part-1

The paper describes a novel technique to harvest Rn laden air from soil gas of natural origin as a highly efficient source of Rn for calibration applications in a walk-in type Rn calibration chamber. The technique makes use of a soil probe of about 1 m to draw soil gas, through a dehumidifier and a delay volume, using an air pump to fill the calibration chamber. Rn concentration in the range of a few hundred Bq m to a few tens of kBq m was easily attained in the chamber of volume 22.7 m within a short pumping duration of 1 h. A new technique referred to as "semi-dynamic mode of operation" in which soil gas is injected into the calibration chamber at regular intervals to compensate for the loss of Rn due to decay and leak is discussed. Harvesting soil gas has many important advantages over the traditional methods of Rn generation for calibration experiments using finite sources such as solid flow-through, powdered emanation, and liquid sources. They are: (1) soil gas serves as an instantaneous natural source of Rn, very convenient to use unlike the high strength Ra sources used in the calibration laboratories, and has no radiation safety issues, (2) does not require licensing from the regulatory authority, and (3) it can be used continuously as a non-depleting reservoir of Rn, unlike other finite sources. The newly developed technique would eliminate the need for expensive radioactive sources and thereby offers immense application in a variety of day to day experiments-both in students and research laboratories.