Variation of the Background Count Rate of the Liquid Scintillation Counter due to Natural Radioactivity

Variation in the background count rate of a liquid scintillation counter due to natural radioactiveity was measured by repeat and cycle modes. The samples used for measuring the background count rate were polyethylene, Teflon, quartz glass and low-potassium glass vials contained the liquid scintillator only. The background count rate of the polyethylene vial was found to be lowest among the four vials. Variation in background count rate was correlated with the concentration of 222Rn which was strongly affected by ventilation in the laboratory. 222Rn and its daughter nuclides giving rise to the variation in background count rate were apparently carried into the detector section not only by adsorption on the vial but also by the solution in the vial material. To reduce the effects of 222Rn and its daughter nuclides, each vial kept in the changer section of the liquid scintillation counter was covered with a “cap”. As a result, variation in the background count rate was found to be considerably reduced for all the vials