Research On Diffusing Issue About Using Accumulation Method To Measure Radon Concentration In The Environment

The United Nations Scientific Committee on the Effects of Atomic Radiation?UNSCEAR?points out,internal exposure dose caused by the environment radon accounts for about half of the effective dose caused by natural radiation source,in the meanwhile,according to the results of epidemiological studies,radon is one of the 19 most important carcinogens.The environmental protection department and some scholars conducted investigations about the radon and its progeny in indoor and outdoor air in some cities,basically mastered the data of environmental radon level,however,accumulative measurement of radon concentration in the air still haven't been taken as monitoring items in our country's radiation environmental monitoring network.Therefore,the monitoring of the change trend in radon concentration level in the air nationwide hasn't been carried out yet.In this paper,based on the sufficient investigation of technical methodsandstandardsofradonconcentration'saccumulative measuring,and by comparing with the current measuring method,we propose the measuring method accordance with China's actual situation in environmental radiation monitoring,namely method of solid state nuclear tract detection?SSNTD?,for radon concentration's accumulative measurement in national control sites.When using the method of SSNTD to measure radon concentration level in the air,we found that,domestic and overseas labs and monitoring stations choose different filter membranes in SSNTD,on account of that different membranes have different radon diffusion ability,compare to those membranes which diffuse fast,membranes with bad diffusion ability has long compensation time,also the calibration factor is smaller,which will influence the accuracy of radon detection when using SSNTD.So,it's necessary to conduct experiment of filter membranes on radon diffusion ability in various humidities,analyze the related factors.On the basis of the principle of the gas permeation through filter membranes,this paper studied the diffusion ability of three types of membranes which used in solid state nuclear track detectors for radon measuring under four different humidity ranges.Among these three membranes,the diffusion ability of cellulose acetate membranes and filter papers are apparently stronger,it takes just 2 to 3 hours to make the radon concentration in diffusion chamber approaches to the radon concentration in source chamber.However,for polyethylene membranes,the radon concentration in diffuse chamber can only achieve about one-tenth of that in the source chamber even if diffuse 10 days.For cellulose acetate membranes and filter papers which have strong diffusion ability,its diffusion ability shows a slightly difference in different humidities,in 95%humidity,radondiffusionabilityisweakerthanother humidities,however,after 2 to 3 hours,the radon concentration in diffuse chamber can also approach to the radon concentration in source chamber,so,influence of humidity on these two membranes are not obvious.The ratio of the diffusion coefficient and membrane thickness of cellulose acetate membranes are from 0.72×10^-5m/s to 2.87×10^-5m/s,the ratio of the diffusion coefficient and membrane thickness of filter papers are from 1.21×10^-5m/s to 4.5×10^-5m/s.But we can't calculate the radon diffusion coefficient of polyethylene membranes owing to that it hasn't reach equilibrium in the experimental period,and according to diffusion diagram,polyethylenemembraneshavethepoorestdiffusion ability,so,influence of humidity is also not obvious.The results show that,compare to polyethylene membranes,cellulose acetate membranes and filter papers are suitable as membranes for radon measurement in solid state nuclear track detector.