Investigation of 220Rn emanation and exhalation from soil samples of Larsemann Hills region, Antarctica

INFLUENCE OF SAMPLING FLOW RATE ON THORON EXHALATION RATE MEASUREMENTS BY THE CIRCULATION METHOD

Researchers have used various methods to obtain the exhalation rates of radon and thoron from soil and building materials. One of the typical methods for radon exhalation rate is the circulation method using an accumulation container, an external or internal sampling pump and a continuous radon monitor. However, it is necessary to consider sampling flow rate if this method is applied to exhalation rate measurement for thoron due to its short half-life. Based on a calibration experiment, the measured thoron concentrations obtained by an electrostatic collection type radon and thoron monitor (RAD7) were found to be influenced strongly by the sampling flow rate. It was also found that the thoron exhalation rate from a soil sample depended on the pressure difference which was proportional to the increasing sampling flow rate. The thoron exhalation rate measured at the generally used sampling flow rate of the internal sampling pump of the RAD7 was overestimated compared with the value at 0 L min-1.

Influence of various factors on the value of thoron emanation coefficient

The “powder sandwich” method was adapted to the measuring equipment at the Laboratory of Radiometric Expertise, IFJ PAN (Kraków, Poland). The versatility of the method has been confirmed. The values of thoron emanation coefficients (f) for 16 materials have been determined. It has been found that the value of thoron emanation coefficient is not directly dependent on the concentration of 224Ra, other factors are also important, e.g. the size of the grains, the inter-grain space and the distribution of radium atoms in the grain. The influence of the grain size on the value of thoron emanation coefficient was investigated.