ABSTRACT
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.
ABSTRACT
Objective To investigate the methods and effects of abdominal and pelvic shielding for pediatric chest CT examinations.Methods The 705-D phantom made by Computerized Imaging Reference Systems (CIRS) was used to replace a 5-year-old child,thermoluminescent dosimeters were set in the abdomen and pelvis to measure the organ and tissue doses.Chest scans were conducted with the routine protocol for pediatric chest CT examinations.Doses to main organs and tissues in the abdomen and pelvis were measured after chest CT scans without lead apron,with lead apron covering anterior of the abdomen and pelvis and with apron wrapping same part,respectively.Results Absorbed doses to some abdominal organs near the irradiation field were up to several mGy in a procedure of pediatric chest CT examination.There were statistically significant differences among the dose values for three different scans at the same location (x2 =16.00,P ＜ 0.05).Statistically significant difference was also found between the dose values for scans,which were measured with wrapping and covering approaches (Z =-2.52,P ＜ 0.05).Compared to the doses in the condition of no shielding,the doses in testis and colon reduced by 71.2％ and 42.3％,respectively,if the abdomen and pelvis was wrapped with a lead apron (0.35 mm Pb),and reduced by 55.9％ and 26.1％,respectively,if the same lead apron was used to cover the anterior of the abdomen and pelvis.Conclusions In pediatric chest CT examinations,the use of a lead apron can effectively shield the abdomen and pelvis,and plays an important role in protection of the gonad and colon.The wrapping measure is worth being recommended.