ABSTRACT
Objective To study the effect of radon exhalation on the external dose model for building material,so as to provide the scientific and precise assessment of external radiation exposure hazard.Methods The mechanism of exhalation of radon from building material was analyzed,mathematical model of correction factor for the effect of radon exhalation was derived and resolved by Matlab program and the relationship between correction factor and diffusion length,surface emanation coefficient and thickness of building material was discussed.The absorbed dose rate induced by several classical building materials was calculated and compared.Results The radon exhalation correction factor was independent of diffusion length and thickness of building material in most cases.Negative correlation was found between radon exhalation correction factor and radon surface emanation coefficient.Radon exhalation correction factor numerically equals to '1-radon surface emanation coefficient'.The relative percentage deviation between absorbed dose rate induced by several classical building materials was in the range of 2.23％-10.02％,for both corrected and uncorrected radon exhalation effects.Conclusions Radon exhalation from building material has a certain effect on external dose model for building material,which should attract attention.It is important to conduct the correction for external dose model by introducing ‘1 -radon surface emanation coefficient’ as the radon exhalation correction factor,in order for the scientific assessment and control of external radiation exposure hazards from building materials.
ABSTRACT
Objective To measure the current environmental radioactivity levels in some districts of Yunnan Province,and to estimate the external doses to local residents.Methods The surface soil,aerosol and water samples were collected and analyzed by HPGe gamma spectrometry.Based on the estimation model selected by Ministry of Health in the nationwide soil survey,the doses to local residents from 238U,226Ra,232Th,40K and 137Cs in environmental samples were estimated.CARI-6 software issued by FAA (Federal Aviation Administration ) was used to estimate cosmic radiation dose to the local population.Results The external annual dose rate to the local people was 1.13 mSv per year,of which 0.52 mSv per year was contributed by natural radionuclides in soil,0.6 μ Sv per year by 137 Cs in soil and 0.61 mSv per year by cosmic radiation.Conclusions The cosmic radiation and natural radionuclides in soil might contribute 99.95％ of external exposure dose,while artificial radionuclide 137Cs contribute 0.05％ of external exposure dose.