Diffusion effects and phosphorescence of samples in liquid scintillation counting

Results of the experiments are presented which carried out to investigate some measuring effects in liquid scintillation counting of water samples. Samples stored in polyethylene couting vials for a long time show detectable decrease in count rate. It was shown that this effect is mainly caused by diffusion of scintillation mixture through the walls of counting vials. Results obtained from the experiments are the following: decrease of count rate by 0.68% per day, and a respective mass of 0.16% per day. It was found that scintillation properties of the scintillator were getting worse after adding water to the sample (the observed decrease of count rate was about 1% per week). The phosphorescence and delayed fluorescence decay time in sample was estimated at 1 hour, for standard sample composition. Directly incident sunlight gives the largest excitation of the sample. (author)