Study On The Key Parameters Of ²²⁰Rn Daughter Regulation In ²²⁰Rn Chamber Flow Field Mode

Radon(including ²²²Rn and ²²⁰Rn)and its daughters are widely distributed in the atmosphere and indoor environment.Radon is the main source of natural radiation to human beings and is listed as the second leading cause of lung cancer after smoking by the World Health Organization(who).In recent years,great achievements have been made in the source of ²²²Rn,environmental pollution and human health hazards caused by ²²²Rn and its progenies.Comparatively speaking,people pay much less attention to the harm of ²²⁰Rn and its progenies in the environment.This is because,on the one hand,in most cases,the dose caused by ²²⁰Rn and its progenies is almost negligible compared with²²²Rn and its progenies.On the other hand,the half-life of ²²⁰Rn is very short(55.6s),and the distribution of ²²⁰Rn in the environment is uneven,while the half-life of ²²⁰Rn progenies(mainly ²¹²pb)is long After 10.6hours,²²⁰Rn and its progenies reached equilibrium,which was caused by many factors.Moreover,the balance factor between ²²⁰Rn and its daughters is affected by the location of the detector in the room and the indoor environment,and its uncertainty is very large,which makes it difficult to measure and evaluate the dose of ²²⁰Rn and its daughters.In view of the above facts,it is necessary to develop a set of standard ²²⁰Rn room with strong regulation ability in order to evaluate the dose caused by ²²⁰Rn progeny more accurately.Based on the existing ²²⁰Rn chamber of South China University and the optimized ²²⁰Rn daughter body compensation technology,this paper establishes a theoretical model of ²²⁰Rn daughter body regulation under the flow field mode of the ²²⁰Rn chamber.In this model,the key parameter of the ²²⁰Rn daughter body circulation loss rate is proposed.It characterizes the loss per minute of the ²²⁰Rn daughter body when circulating in the ²²⁰Rn chamber.The circulation loss rate is related to the circulating flow rate,the box structure,and the particle size of the daughter body aerosol.It is the most critical parameter for the control of the ²²⁰Rn daughter body in the ²²⁰Rn chamber.It includes The loss of²²⁰Rn daughter due to deposition and wall attachment during the regulation of ²²⁰Rn daughter is simplified,which simplifies the regulation model and more directly reflects the law of ²²⁰Rn daughter loss.In this paper,a method for measuring the circulation loss rate of²²⁰Rn daughters is established based on the behavior of ²²⁰Rn daughters in the flow field mode of the ²²⁰Rn chamber.The experimental results show that the relative standard deviation of the Th B concentration in the ²²⁰Rn sub-body source box measured within one day is 1.5%,and the Th B concentration in the main chamber The relative standard deviation is8.74%,and the degree of stability can ensure the accurate measurement of the ²²⁰Rn progeny circulation loss rate.The effect of wind speed on the circulation loss rate of ²²⁰Rn daughters The experimental results show that with the increase of the fan frequency and wind speed,the circulation loss rate of ²²⁰Rn daughters increases rapidly;the effect of aerosol particle size on the circulation loss rate of ²²⁰Rn daughters The experimental results show that when When the aerosol particle size is below 200nm,the cycle loss rate is low and basically remains unchanged.When the aerosol particle size reaches 300nm and larger,the cycle loss rate of ²²⁰Rn progeny increases rapidly,which is not conducive to the regulation of²²⁰Rn progeny concentration in the ²²⁰Rn chamber.The measurement results of the circulation loss rate provide key parameters for the regulation of the ²²⁰Rn chamber ²²⁰Rn progeny in the flow field mode,and the study of related influencing factors has guiding significance for the selection of regulation conditions.The experimental results of the sampling method show that the downwind sampling has little disturbance on the stability of ²²⁰Rn progeny concentration in the flow field mode of ²²⁰Rn chamber,and the relative deviation of ²²⁰Rn progeny concentration measured by this sampling method is smaller;in order to directly measure the output ²²⁰Rn progeny concentration of ²²⁰Rn progeny source box,a special sampling device is designed,and the measurement results of this sampling device can more accurately reflect the ²²⁰Rn progeny source chamber The concentration of ²²⁰Rn progeny added to the main chamber.