Theoretical evaluation of calibration factor for CR-39 track detector for alpha radioactivity measurement in natural water

Highlights: • A simple track-etch method developed for determining alpha radioactivity of water. • Calibration factor for CR-39 evaluated for alpha radioactivity measurement in water. • Drinking water samples collected from different water points in West Bengal, India. • Alpha radioactivity of samples is compared with worldwide values reported in articles. • Novelty of the present study is the evaluated calibration factor and the method. A simple track-etch method by using CR-39 detectors has been developed for determining the total alpha radioactivity level in natural water. The detectors are immersed into water sample for alpha exposure. Alpha particles generated near the detectors create latent tracks, which are a measure for the alpha radioactivity of the sample. Calibration factor (CF) evaluation for a track detector is a part of this method. It is evaluated by considering major alpha-emitters present in natural water and taking into account the actual geometry of the set-up. The method for evaluating the CF is based upon the calculating range of alpha particles in water and the estimating effective volume of water around the detector. The evaluated CF is found to be$\left(116.18\pm 9.88\right)Bq.l^{-1}.{\left(tracks.c{m}^{-2}.h^{-1}\right)}^{-1}$. This method has been used to determine the total alpha radioactivity of $52$ drinking water samples collected from different tube-well and tap water points at eight districts of Indian state of West Bengal. Measured radioactivity values vary from $\left(15.17\pm 1.29\right)Bq.l^{-1}$ to $\left(45.67\pm 3.88\right)Bq.l^{-1}$ with a mean value of $\left(27.64\pm 2.35\right)Bq.l^{-1}$. These radioactivity values are compared well with the worldwide alpha activity values reported in research articles. It is observed that the measured alpha radioactivities are below the recommended reference level and hence, the drinking waters of the sampling sites are safe for consumers. The CF evaluated and the experimental method developed in the present study can also be utilized in the radioactivity research field. Data obtained in the present study may serve as a good baseline.