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ABSTRACT
Radon in soil is a valuable radioactive tracer in earth science, especially for earthquake and volcanic precursors. For the purpose of continuous measurement of radon-in-soil concentration in-situ, a new-designed measurement system was developed. Calibration and experiments for humidity response correction were carried out in details, and field measurement of vertical profile with 7 radon probes at different depths was performed. Calibration results show that the sensitivity of the radon probes is 16.1 ± 1.0 cph (kBq m−3)−1, and the lower level detection limit is 231 ± 15 Bq m−3 for 1-hour measurement cycle under the absolute humidity of 32.8 g m−3. Field measurement results show that radon concentrations at different depths change with time and increase with depth in the soil. The vertical profile presents a negative exponential distribution with different diffusion length in sunny days, while rainfall can disturb the vertical distribution and lead to increase of radon concentration in the near ground surface. Radon concentration in underground deeper than 80 cm appears quite stable and hardly affected by rainfall in our observation.
Disclosure statement
No potential conflict of interest was reported by the author(s).