Non-destructive determination of uranium, thorium and ⁴⁰K in tobacco and their implication on radiation dose levels to the human body

The naturally occurring radionuclides of ²³⁵U, ²³⁸U and ²³²Th and their daughter products are a potential major source of anthropogenic radiation to tobacco smokers. Often overlooked is the presence of ⁴⁰K in tobacco and its implication to radiation dose accumulation in the human body. In this study, these three radiation sources have been determined in four typical US cigarettes using neutron activation analysis (NAA). The NAA reactions of ²³⁸U(n,γ)²³⁹U, ²³²Th(n,γ)²³³Th and ⁴¹K(n,γ)⁴²K were used to determine ²³⁵U, ²³⁸U and ²³²Th and ⁴⁰K, respectively. The activity of ²³⁸U can easily be determined by epithermal NAA of the ²³⁸U(n,γ)²³⁹U reaction, and the activity of ^235,234U can easily be deduced. Using isotopic ratios, the activity due to ⁴⁰K was found by the determined concentrations of ⁴¹K (also by epithermal neutrons) in the bulk material. Each gram of total potassium yields 30 Bq of ⁴⁰K. The annual effective dose for smokers using 20 cigarettes per day was calculated to be 14.6, 137 and 9 μSv y^-1 for 238,^235,234U, ²³²Th and ⁴⁰K, respectively. These values are significantly lower that the dose received from ²¹⁰Po except for ²³²Th. (authors)