Study On Simulative Measurement Of Radon And Thoron Progeny Deposited In Human Respiratory Tract

Objective The health effects from radon exposure has become as a world-widelyconcerned issue and an important research topic in the field of public health.Accurateestimation of the internal dose from radon exposure is essential to assess the healtheffects.Generally used dosimetric methodology exist large uncertainty,while othermore accurate methods are still difficult to be widely spread due to the cost andcomplicacy of the necessitated equipments.For more accurate estimation of theinternal dose from radon exposure,this study was mainly aimed to accurately simulateand measure the radon and thoron progeny deposited in the respiratory tract,and todevelop a set of device which is suitable for large-scale field surveys.Furthermore,this study was also expected to provide some preliminary results about the fractions of²²²Rn/²²⁰Rn progeny deposited in different regions of the respiratory tract in the generalliving environment.Methods According to the main purposes of this study,the study were divided intothe following three parts.1) As the deposition mechanism of aerosols on wire screens and the respiratorytract are the same.The metal wire screens were used to simulate the deposition ofaerosol in the respiratory tract.Based on the collection theory of wire screens andtaken the typical aerosol size distributions in indoor and outdoor as well as mineenvironments,different configurations of wire screens were seriously selected forsimulating both the extra thoracic (ET) region and tracheobronchial (TB) regions.Throughout the comparisons with the calculation results from the LUng DoseEvaluation Program (LUDEP) and considering the difference of aerosol sizedistributions between the used reference values and those in actual environments,thecombination of wire screens and the sampling flow rates were optimized.2) By using the technique of solid state nuclear track detection,a new portabledevice was optimizing designed for integral measurements of ²²²Rn/²²⁰Rn progeny based on experimental studies about radiation properties of the detector and thediscrimination of ²²²Rn and ²²⁰Rn progeny.According to the stimulation resultsmentioned above,a set of sampling heads simulating the respiratory tract weredesigned to fit with the device for finally realizing the simulation measurements of²²²Rn and ²²⁰Rn progeny deposited in the respiratory tract.Inter-comparisonexperiments were performed in both a radon chamber and common environments forevaluation of the key performance of the final device.3) Field measurements were carried out with the device developed by this study inboth the indoor and outdoor environments,and the typical deposition fractions of²²²Rn/²²⁰Rn progeny in different regions of the respiratory tract were summarized.Results The major results of this study are described as below.1) One single 200-mesh wire screen and four 635-mesh wire screens areappropriate for simulating the aerosol depositions in the ET region and TB region ofthe respiratory tract,respectively.The optimized sampling flow rates are 0.11 m·s^-1and 0.12 m·s^-1 for measurements in the indoor/outdoor and mine environments,respectively.The calculated deposition fractions in the ET and TB region for theselected combinations of wire screens at the selected sampling flow rates only differfrom those calculated by LUDEP within±1.5%.2) Inter-comparison results showed that the measurement uncertainty for ²²²Rn/²²⁰Rn progeny concentrations with the new device was less than 15% in both a radonchamber and common environment.The difference between the experimental andtheoretical fractions of ²²²Rn/²²⁰Rn progeny deposited in different regions of therespiratory tract was less 22%.No obvious relation was found between the uncertaintyof results and environmental parameters,such as ²²²Rn/²²⁰Rn progeny concentrationsand the size distribution of aerosols.3) Field measurement indicated that the typical fractions of ²²²Rn progeny depositedin the ET and TB regions were 5.15% and 5.61% in common offices,respectively.The results were 5.41% and 5.45% in general bed rooms,and were 6.70% and 4.24%for outdoor environment,respectively.No significant difference was found betweenthe deposition of ²²²Rn progeny and ²²⁰Rn progeny.Conclusion The combinations of wire screens selected in this study cansuccessfully stimulate the deposition of aerosols in the respiratory tract.Within an acceptable uncertainty of 20%,the device developed in this study is able to accuratelyassess both the amount and fractions of ²²²Rn/²²⁰Rn progeny deposited in therespiratory tract.The internal dose from radon exposure can be directly and moreaccurately evaluated with the measurements by the device.Furthermore,theportableness and cost effectiveness as well as simplicity make the new device suitablefor carrying out large-scale surveys of radon exposure,and its measurements aredirect and reliable.