Transfer of 226Ra and 137Cs from tea leaves to drinking tea

Background: Two of the important radionuclides which are entered to environment and human diet are radium-226 (226Ra) and cesium-137 (137Cs). It is clear that the methods for preparation of foods such as peeling, washing, cooking or frying can affect the dose which is received by human due the to consumption of foodstuffs. An experiment has been performed at the environmental monitoring section of NRPD, aiming to measure the transfer of 226Ra and 137Cs from the tea leaves to drinking part of tea. Materials and Methods: Tea samples were pulverized to obtain a homogenous matrix which was weighed and placed in 1000 cm3 Marinelli beaker. After making tea, the liquid tea and tea-discard were analyzed separately. Measurement of 226Ra and 137Cs was performed by gamma spectrometry system using a high purity germanium (HPGe) detector with 40 % relative efficiency. The detector was shielded by 10 cm lead an all sides with cadmium -copper as liners. Results: It was found that the activity concentration transferred from tea leaves to drinking tea for 137Cs and 226Ra are less than 2% and 17% respectively. Conclusion: On the basis of these measurements it seems that no significant levels of radioactivity of 226Ra and 137Cs can be found in drinking part of tea. The low concentration of the mentioned radionuclides in drinking tea is mostly due to tea dust and can be removed by its washing before preparing tea.