Determination of alpha-emitters in Brazilian tobacco

The decay products of uranium and thorium natural series are widely distributed in all the terrestrial crust. Their concentrations are considerable in the phosphates utilized as fertilizer in the Brazilian agriculture. In this work analysis was performed on 238U, 234U, 232Th, 226Ra and 210Po in 22 Brazilian tobacco samples. The results showed 238U and 234U are in isotopic activity equilibrium (0.5±0.2 mBq/g). The equilibrium was not reached in the case of thorium isotopes: the 228/232Th ratio was about 6.4. The average values obtained were 34.3 mBq/g for 228Th and 5.4 mBq/g for 232Th. The 226Ra values were higher than its radioactive precursor, 238U. This can be explained by the high affinity of radium to tobacco plant and the uranium removal during physical and chemical processes. The high concentration of 210 Po(20 mBq/g) in tobacco samples may be due to radon daughter products being electrically charged and then attaching themselves to inert dusts, which then become attached to tiny hairs on tobacco leaves. The results of this work are consistent with values presented in specialized literature. (author) 15 refs.; 4 tabs