Measurements of alpha radioactivity in thermal power plant effluents employing CR-39 detector based improved alpha track detection method

Highlights: • New chemical etching technique was optimized for revealing alpha tracks in CR-39. • Tetraethyl ammonium bromide, a phase transfer catalyst, enhanced chemical etching. • Alpha track appearance improvements in less etching time. • Newly introduced etching method was applied for low level alpha track detection. Natural radioactivity is released into the environment during the combustion process of coal at various thermal power plants. Coal contains higher contents of α-emitting radionuclides such as ²³⁸U, ²³²Th along with their decay elements, which pose a potential health risk to the population. In the present studies, the effluent waste samples were collected from a coal fired Thermal Power Plant. Samples were collected in the form of solid residues and filtrates. CR-39 detector pieces were then exposed for varying time with residue and filtrate samples for registering the alpha tracks for α-detection and measurement. Thus, registered alpha particles in CR-39 detectors were revealed by employing the conventionally used 6M NaOH/KOH etchant and 5% tetraethyl ammonium bromide (TEAB) as a phase transfer catalyst in 6M NaOH/KOH etchant. Under both compositions of the etchants, CR-39 detectors were etched at 60 °C for 6 h for developing alpha tracks for observations under optical transmission microscope. Alpha track densities (T_d) and alpha track diameters in the etched CR-39 detectors for all samples were measured. The introduction of new chemical etchant effectively improved the uniformity in distribution of alpha tracks, enhanced the track density, and reduced the time of track revelation in CR-39 detectors. Therefore, it could be concluded that the phase transfer catalyst TEAB was highly effective in the etchant for alpha track revelation and detection as compared to conventionally used 6M NaOH etching method. Apart from measuring alpha radio activities, the amounts of ²³⁸U & ²³²Th in the samples were also measured by ICP-MS for understanding the alpha radio activities measured in the coal samples.