Regulation And Control Methods For The Unattached Fraction Of The ²²⁰Rn Progeny In A ²²⁰Rn Progeny Chamber

The unattached fraction of the ²²⁰Rn progeny is one of the key parameters in lung dose evaluation models.To accurately evaluate the exposure hazards of the ²²⁰Rn progeny,it is necessary to conduct surveys of the characteristic parameters such as the ²²⁰Rn progeny concentration and the unattached fraction under various typical environmental conditions.For this reason,it is necessary to establish a ²²⁰Rn progeny chamber that can realize the regulation of the distribution characteristics of the unattached fraction of the ²²⁰Rn progeny to meet the requirements for measuring the characteristic parameters of the ²²⁰Rn progeny and for calibrating the instruments as well as for ensuring the reliability of the measured data such as the ²²⁰Rn progeny concentration and the unattached fraction at the monitoring site.A ²²⁰Rn progeny chamber that can stably regulate different unattached fraction of the ²²⁰Rn progeny was established in this study.A recirculation loop to eliminate the effects of the sampling and a loop connected to the dilution chamber to supplement the carrier aerosol were set up.Also,a theoretical model regarding the regulation of the unattached fraction of the ²²⁰Rn progeny was established.When the sampling flow rate is set to 5L/min,the measuring device for the unattached fraction of the ²²⁰Rn progeny and the activity particle size distribution is redesigned:The Graded Screen Array（GSA）composed of30 wire mesh,100 wire mesh,200 wire mesh,and 400 wire mesh.The combination of a single-layer wire screen and a filter membrane was used to collect the unattached fraction share of ²²⁰Rn progeny,and the EM algorithm and Towmey algorithm for the inverse calculation of activity particle size distribution of ²²⁰Rn progeny were compiled.And preliminary measurement of activity particle size distribution of ²²⁰Rn progeny.The experimental results showed that the ²²⁰Rn progeny chamber could control the aerosol concentration under different typical environmental conditions（from the concentration in an extremely clean environment（about 30/cm³）to that of the normal indoor environment（about 7500/cm³））and maintain it stably for a long time.the stability in the ²¹²Pb concentration during the continuous samplings was higher than10.1%and the unattached fraction of ²¹²Pb was larger than 9.9%.The relative standard deviation（RSD）between the theoretical and the experimental values of the ²¹²Pb concentration was within 16.7%and the RSD between the theoretical and experimental values of the unattached fraction of ²¹²Pb was within 33.1%.It was shown that it was feasible to guide the actual control of the unattached fraction by the presented theory.The ²²⁰Rn progeny chamber can realize the regulation of the distribution characteristics of the unattached fraction of the ²²⁰Rn progeny under different typical environmental conditions,and can initially meet the requirements of the ²²⁰Rn progeny characteristic parameter measurement method and instrument calibration.The ²²⁰Rn progeny activity particle size distribution measurement results show that there is basically no difference between the results of the two reverse calculation algorithms,and the activity median diameter is in good agreement with the known literature.The GSA designed in this study basically meets the actual measurement needs.