Influence of urbanization on radon potential in Zhongshan City in the southern China

Abstract:

Radon and radon progeny are the most important contribution to dose from natural sources of radiation. Most studies have demonstrated an increased risk of lung cancer at high concentration of radon for the public. Radon potential map is an essential approach for radon risk assessment.

The radon potential map is based on the measured data of soil gas radon concentration and soil air permeability, combined with GIS technology, in Zhongshan City in the Southern China. The preliminary radon survey in ZC was conducted using a portable semiconductor radon monitor RAD-7 and soil air permeability instrument Rad-jok, covering a total area of 1800 km2. The sampling depth for soil gas radon measurement in the field was at the depth of 80 cm below the ground. ²²²Rn activity concentrations varyed between 0.74 and 158 kBq/m3, and ²²⁰Rn between 0.02 and 235 kBq/m3 in soil gas. The average value of ²²²Rn and ²²⁰Rn was 67.6 and 74.8 kBq/m³, respectively. The results show that: (1) the characteristics and distributions of ²²²Rn/²²⁰Rn concentration from soil gas in ZC are obviously related with local lithology (the Middle and the Late Jurassic and the Cretaceous biotitic-granite) and geological formation. High ²²²Rn/²²⁰Rn concentrations were observed in soil gas in the outcrops of weathered granite or filled back granite sands. (2) The distribution model of ²²⁰Rn is as same as that of ²²²Rn. The Wuguishan Mountain areas and in the south-east areas of ZC, covering with granite rocks, are high radon risk districts; the central zones in ZC are low radon potential areas, and part of the northern districts are medium radon potential areas. (3) Urbanization has increased local radon risk in some districts in the west and the north of ZC, where now covering several meters depth weathered granite products, but deposited the Quaternary sediments near surface before.

The research was supported by National Natural Science Foundation of China (No. 41474107, No.41274133 and 41074096).