Determination of radioactivity in maize and mung beans grown in the neighborhood of Minjingu phosphate mine, Tanzania

Abstract

Two staple foods (maize and mung beans) which were cultivated in Minjingu village, where there is phosphate deposit in Tanzania, were collected directly from the farms. The activity concentrations of ²²⁶Ra, ²²⁸Th and ⁴⁰K were determined in the maize and mung beans samples using γ ray spectrometry employing HPGe detector of relative efficiency of 51.0 %. The mean radioactivity level in the food samples were found to be 21.01 ± 0.8 Bq/kg (mung beans), 25.6 ± 0.7 Bq/kg (maize) for ²²⁶Ra, 62.6 ± 1.1 Bq/kg (mung beans), 72.9 ± 1.0 Bq/kg (maize) for ²²⁸Th and 542.9 ± 8.6 Bq/kg (mung beans), 434.6 ± 18.7 Bq/kg (maize) for ⁴⁰K. The radioactivity content of the maize and mung beans from Minjingu village were higher than that of similar food samples collected from Bukombe district in Geita Region in Tanzania. The total annual effective dose for consumption of ²²⁶Ra and ²²⁸Th by adults was calculated to be 2.003 ± 0.044 mSv/year, which is higher than the annual dose limit of 1 mSv/year recommended by the ICRP for the general public. Hence a conclusion could be made that food crops cultivated at Minjingu village might expose the population to high radiation dose which might be detrimental to their health.

Keywords: Radioactivity, annual effective dose, Minjingu Phosphate mine, High Background Radiation Area