Empirical compensation for the precipitation effect in the measurement of gross alpha content in drinking water.

In this experimental work the co-precipitation procedure is used to prepare samples of water for measurement of their gross alpha concentration. It has been suspected that total dissolved solids (TDS) in the water influence the results of radioactivity counting. The dissolved solids may influence the chemical procedures of sample preparation or the detection and counting of the alpha particles emitted by the radionuclides in the drinking water. The aim of this study was to check the hypothesized influence of the TDS on the counting procedure and offer countermeasures to compensate for this influence. In the frame of this study more than six hundred measurements were conducted on samples to determine their gross alpha concentration. The variety of samples represents different controlled dilutions with known TDS values. Each sample was measured several times repeatedly and independently, and also three runs of experiments were conducted, each run subjected to independent application of the co-precipitation procedure. The analysis of the accumulated experimental data revealed an effect of the TDS values on the corresponding number of counts from the samples which may be due to self-absorption in the co-precipitated layer. An empirical correction function for the TDS effect is presented in this work. Data analyses pointed out the experimental and procedural conditions required to allow an acceptable level of sensitivity in terms of the minimum detectable activity (MDA) to ensure that the water under inspection meets the standards.