Study On The Determination Method Of Thoron Reference Concentration And Control Performance For The Thoron Chamber

With further research of ²²²Rn,which isotope ²²⁰Rn has been attracting much attentions.²²⁰Rn is a kind of radioactive inert gas,which co-exists with its progeny in the environment.Together with ²²²Rn and its progeny,²²⁰Rn and its progeny are the main sources of natural radiation.Note that when the volume activity of the progeny of ²²²Rn and ²²⁰Rn are equals,the inner irradiation to humans caused by the progeny of ²²⁰Rn beyond the progeny of ²²²Rn.From the surveys of radionuclides in multiple areas all over the world,many areas are shown to be the high thoron background area,where cave dwellings in Gansu province,Yangjiang city,Zhuhai city and other regions are included.Besides,in some occupational places where thorium resources are exploited,the ²²⁰Rn concentration in the environment is higher than other places obviously.Therefore,the hazards caused by ²²⁰Rn and its progeny should call for highly attentions and developing accurate hazard assessments.The measurement methods of thoron concentration and the advantages and disadvantages of measure instruments,as well as the relatively appropriate measurement methods to be applied in practical work have been introduced.The gas-through and static measurement method by using single scintillation cell has been regarded as a standard method to determine the concentration of thoron.Based on the flow-through solid thoron source,parameters analysis and measurement have been carried out on the measuring device of gas-through scintillation cell method,and the accuracy of this device at three test mode has been verified under different ²²⁰Rn concentration.RAD 7 portable detector was selected as the representative instrument of alpha energy spectrum.The sampling flow rate is one of the most important factor which influences the accuracy of RAD 7 measuring the thoron concentration.So the modifying factor of RAD 7 measuring thoron concentration under different sampling flow rate has been discussed by theoretical analysis and experimental verification.According to the actual flow rate,the result of RAD 7 measuring thoron concentration should be modified.And verified the accuracy of the gas-through scintillation cell method and alpha energy spectrum by comparing the deviation of measurement result.The regulation of different thoron concentration in ²²⁰Rn chamber has been realized by using different activity ²²⁰Rn sources,connecting different volume delay bottles and adjusting flow rate.And the homogeneity and stability of ²²⁰Rn concentration distribution in the ²²⁰Rn chamber has been tested through continuous monitoring of ²²⁰Rn chamber by RAD 7.