基于低本底高纯锗γ谱仪测量茶叶和烟草中^(210)Pb和^(40)K的比活度

Measurement on Specific Activity of ^(210)Pb and ^(40)K in Tea and Tobacco via Low Background High Purity Germanium Gamma Spectrometer

茶叶和烟草中存在^(210)Pb和^(40)K等放射性核素,其放射性含量一直备受关注。本研究选择基于低本底高纯锗γ谱仪的γ能谱方法,并结合Geant4无源效率刻度技术,对典型的茶叶和烟草样本进行了^(210)Pb和^(40)K比活度测量。其中,低本底高纯锗γ谱仪由Canberra BEGe 5030高纯锗探测器和15 cm厚低本底钢+2 cm厚高纯无氧铜屏蔽室组成,在30~3 000 keV能量范围内,全谱计数率为1.98 s-1。基于以上实验设备,选择了4种茶叶和5种产地的香烟作为测量对象,测量结果显示,茶叶中^(210)Pb的比活度为8.15~49.67 Bq/kg,^(40)K的比活度为296.58~351.69 Bq/kg;烟草中^(210)Pb的比活度为21.74~31.16 Bq/kg,^(40)K的比活度为470.15~522.88 Bq/kg。根据样品中^(210)Pb的平均比活度估算,饮茶导致的^(210)Pb有效剂量应小于35.15μSv/a,吸烟导致的^(210)Pb有效剂量约为11.00μSv/a,饮茶和吸烟造成的相应核素的内照射剂量对人体健康的影响均较小。

Radionuclides,such as^(210)Pb and^(40)K,exist in tea and tobacco and their corresponding contents provoke wide concern.Earlier studies show that the specific activities of these radionuclides in tea and tobacco are generally higher than that in other foodstuffs like grains,meat and vegetables,which suggests that the consumption of tea and tobacco should lead to higher internal radiation dose in comparison to other foodstuffs.Therefore,it is necessary to constantly monitor the radioactivity levels of tea and tobacco.To facilitate the measurement,a customized low background high purity germanium(HPGe)gamma spectrometer was developed,where the combination of 15 cm thick low-background steel and 2 cm thick high-purity oxygen-free copper served as passive shielding and a Canberra BE5030 HPGe detector was used for gamma-ray detection.In addition,the Monte Carlo simulation platform Geant4 was employed to perform source-free efficiency calibration in measurements.Based on the developed customized low background high purity germanium(HPGe)gamma spectrometer,four typical kinds of tea and five typical kinds of cigarettes were chosen for measurements.The Geant4 simulations for source-free efficiency calibration show that the detection efficiencies on characteristic gamma-rays of^(210)Pb(46.5 keV)and^(40)K(1460.8 keV)emanating from samples are approximately 17.2%-18.7%and 2%,respectively.Meanwhile,analyses on the measured gamma-ray spectra indicate that the specific activities of^(210)Pb and^(40)K in tea samples range from 8.15 Bq/kg to 49.67 Bq/kg and 296.58 Bq/kg to 351.69 Bq/kg,respectively,while those of cigarette samples range from 21.74 Bq/kg to 31.16 Bq/kg and 470.15 Bq/kg to 522.88 Bq/kg,respectively.The average specific activities of^(210)Pb and^(40)K in tea samples are 21.21 Bq/kg and 327.12 Bq/kg respectively,while those of cigarette samples are 26.86 Bq/kg and 499.86 Bq/kg respectively.The activity concentration of^(40)K in humans is readily regulated by metabolism,whereas^(210)Pb is a bone-seeking element with a biological half-life of about 10 years.For this reason,the effective dose of^(210)Pb is of more concern.Based on the average specific activities measured from samples,the effective doses resulted from^(210)Pb uptake are estimated to be less than 35.15μSv/a via drinking tea,and about 11.00μSv/a via smoking.The above results suggest that the internal radiation dose from drinking tea is relatively insignificant,smoking cigarettes made by tea or tobacco should be discouraged considering other deleterious effects from smoking.