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Objective To investigate the levels and distribution of radon in dwellings in Shenzhen cities of China.Methods A total of 108 low-,multi-,middle-and high-rise buildings were selected.Indoor radon concentrations were measured by using solid track detector.Results The arithmetic mean of indoor radon concentrations in Shenzhen was 64 Bq/m3,and geometric mean was 58 Bq/m3,in range of 15 to 155 Bq/m3.The average indoor radon concentration in Bao'an district was 50 Bq/m3 with the lowest value,and that in Pingshan new district was 87 Bq/m3 with the highest value.There were 12 measuring points where indoor radon concentrations were higher than 100 Bq/m3 in Shenzhen,accounting for 11.1％ of the total number.Shapiro-Wilk test showed that the frequency distribution of indoor radon concentration in Shenzhen follows lognormal distribution (P ＞ 0.05).The indoor radon concentrations showed a downward trend from 1990 to 2015.The indoor radon concentration decreases with the elevated floors except 10th and above floors.Conclusions The indoor radon concentrations in Shenzhen increased by 35％,compared to the previous investigations.It is recommended that efforts continue to improve radioactive materials standards about building material and to enhance the natural ventilation in high-rise buildings in order to lower the radiation hazards from radon.
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Objective To establish an accurate method for estimating the indoor gamma dose rate from decorative stones.Methods Combining a room model with decorating conditions,the gamma dose rates and dose rate conversion factors (DCF) at 1 m above the floor in the room center were calculated with the Monte Carlo simulations,and the calculation results were verified through experiments.Based on the results,the limit of radionuclide contents in stone materials was further discussed.Results The DCF increases with the increase of area or thickness of decorative stones in the same room.The increase of DCF with the thickness of decorative stone is approximately linear.The DCF also increases with the area of decorative stones,but the increasing trend slows down.For the same decorative stones,the smaller the room,the larger the increase of gamma dose rate.Experimental results were consistent with the simulation results within ± 20％.Conclusions The increase of indoor gamma dose rate depends not only on the radionuclide contents,but also on the area and thickness of the decorative stones as well as the room size.The method used in this study can be used to estimate,more accurately than ever,the additional external exposure to residents due to decorative stones,and it provides a theoretical basis for revising the limit standard on radionuclide contents in decorative materials.
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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.
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Objective To assess the accuracy and precision of γ-spectrometry analysis, and to obtain accurate and valid measurement results in the middle term and long term. Methods A nationwide intercomparison on gamma-ray spectrometry measurement of activity concentration of 226Ra, 232Th and 40K in soil and building material was organized by National Institute for Radiological Protection( NIRP) , China CDC. Results 15 laboratories participated in this intercomparison, with 13 laboratories produced acceptable results. Only 2 laboratories were classified as " not acceptable" , including one for inappropriate accuracy in determination of 40K and another for inappropriate precision determination of 226Ra in both kinds of the samples. Through comment and discussion, the second round intercomparison got satisfactory results. Conclusions The overall measurement results of samples for intercomparison are in close agreement with the reference values. Most of the laboratories involved in the intercomparison have good ability in γ-spectrometry analysis.