A study of geometric parameters for Marinelli beaker to improving the robustness of the detection efficiency

We have optimized the shape of a Marinelli beaker for a radioactivity analyzer using an NaI(Tl) scintillator with an unfolding technique to improve the robustness of detection efficiency for various uncertain factors such as over-and-short amounts of the measurement sample or misalignment of the Marinelli beaker for the measurement of foodstuffs or environmental samples. The effect of changing each geometric parameter which controls the shape of a Marinelli beaker on the detection efficiency was investigated on the basis of quality engineering. The results of parametric calculations by adjusting these geometric parameters showed that the variance of detection efficiency depends on the distance between the centroid of a specified amount of measurement sample and the centroid of the NaI(Tl) scintillator. As the result of optimization, the variance of detection efficiency has been reduced to about 10 percent at a maximum for various uncertain factors even when a radioactive substance was eccentrically concentrated in the upper or lower half of a measured sample. The results of a performance evaluation using a divided Marinelli beaker with certified reference brown rice showed that the variance of measured radioactive concentration was about 10 percent even when a radioactive substance was eccentrically located in the upper or lower half of a measured sample. (author)