Abstract:
Radionuclides, such as
210Pb and
40K, 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
210Pb (46.5 keV) and
40K (1 460.8 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
210Pb and
40K 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
210Pb and
40K 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
40K in humans is readily regulated by metabolism, whereas
210Pb is a bone-seeking element with a biological half-life of about 10 years. For this reason, the effective dose of
210Pb is of more concern. Based on the average specific activities measured from samples, the effective doses resulted from
210Pb uptake are estimated to be less than 35.15 μSv/a via drinking tea, and about 11.00 μSv/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.