A Preliminary Investigation On Thoron And Its Progeny In Bayan Obo Area

China is a big country of rare earth,and the reserves of rare earth mining in Bayan Obo are even ranked the first in the country.In recent years,the rare earth mining industry has been developing rapidly which brought us great economic benefits,but also cause pollution to the environment,resulting in the deterioration of the human environment.For example,the natural radioactive thorium isotopes have been exposured to the environment with the exploitation of rare earth ores.²³²Th not only causes potential radiation hazards by gamma rays,but also produces radioactive gas ²²⁰Rn,which are more harmful to the human body than ²²²Rn at the same concentration.In this paper,Inner Mongolia Bayan Obo Mining District is the major study object.Based on the measurement of the ²²⁰Rn and it's daughter using RAD-7 of Durridge and ERS-RDM-2S of Tracerlab,the indoor and outdoor ²²⁰Rn and it's daughter concentration levels were investigated in this area.compared with the reference points in Beijing,the survey results show that:?1?The ²²⁰Rn concentration of indoor in Baiyun Obo area ranges from 16.7Bq/m³ to 40.1 Bq/m³,with an average of 29.0+8.5 Bq/m³,about three times of that in Beijing;and the EEC_Th ranges from 0.485 Bq/m³ to 1.104 Bq/m³,with an average of0.801+0.034 Bq/m³,which is about 10 times of that in Beijing.?2?In order to study the influence of different measurement heights,at outdoor investigation sites,we measured ²²⁰Rn and its daughter concentration at 10 cm and 1m above ground.The results show that the ²²⁰Rn concentration decreases rapidly with the increase of measurement height,while it's daughter concentration?EEC?changed with height is not obvious.At the height of 1 m above ground,the concentration of²²⁰Rn in Baiyun Obo area ranges from 30.1 Bq/m³ to 44.9 Bq/m³,with an average of35.3 Bq/m³,which is about 7 times of that in Beijing.?3?Based on the data of radioactive risk assessment,the annul effective dose equivalent?AEDE?in this area is estimated to be 0.14 mSv-0.31 mSv,with an average of 0.22 mSv,which is 10 times of that in Beijing.