Study On Method Of Radon Measurement With Activated Charcoal

Radon(²²²Rn)is a radioactive noble gas existing in nature.Radon and its decay products are responsible for about 50%of human exposure to natural radiation.Radon is the major risk of lung cancer second only to smoking,and has been classed as one of 19kinds main carcinogenic substances by the WHO.Because of the significant health risk of radon,monitoring and controlling radon concentration and exhalation rate is of great importance.The activated charcoal method is simple to operate and of low cost,and has always been one of the main ways to measuring radon.This paper studies some issues of activated charcoal method in the context of inadequate studies of activated charcoal method.In this paper,a new method of calibrating detection efficiency of activated charcoal canister has been presented.Compared with traditional ways,the new method do not need liquid standard radium source and takes lesser time to complete calibration.Using this method,the detection efficiency of activated charcoal canister based on total counts was calibrated for six times,and the standard deviation did not exceed 10%,which proved the stability of this method;The average results of six calibrations was compared with the result of Monte Carlo simulation,and their relative deviation was 15.95%,which proved the accuracy of this method.A theory of dynamic accumulation of radon by activated charcoal has been presented,and the reliability of the theory was tested by designed experiments;The saturated adsorption coefficient was presented which can be used to measure the static adsorption ability of activated charcoal.Experiments show that the saturated adsorption coefficient and the adsorption ability of activated charcoal decrease with increasing the temperature and water adsorption rate and increase with increasing the particle size of activated charcoal.Take the measurement of surface radon exhalation rate with charcoal canister as an example,We study the uneven distribution of adsorbed radon in the charcoal bed and its influences on detection efficiency calibration.Results show that increasing exposure time or using activated charcoal of higher diffusion coefficient can make radon in the activated charcoal well-distributed and reduce calibration error;A constant radon exhalation rate does not influence the distribution of radon in activated charcoal,but a changing exhalation rate does influence the distribution.The greater the change of exhalation rate,the more uniform the radon is distributed.Further study shows that measuring gamma ray counts of charcoal canister by take the up side and down side of canister against gamma gay detector respectively and average the two counts as the final measuring result can almost eliminate calibrate error.