Development of Faced-Type Double NaI(Tl) Scintillation Detector System for Measurement of Radioactive-Cesium Concentration

Abstract

A low-cost and high-performance gamma-ray spectrometer has been successfully constructed by using 3≤f × × 3≤ NaI(Tl) scintillation probes, standard lead bricks and others for the measurement of radioactive-cesium concentration of various surrounding materials. A faced double detector system with signal mixing has been employed for the improvement of total-absorption detection efficiency for radioactive-cesium. Uniquely-shaped containers covering the double detectors have been made of acrylic pipes and plates. The total-absorption detection efficiency for radioactive-cesium in the homemade container was experimentally determined by using a standard voluminous source made of soil in Fukushima. The detection efficiency determined from the experiments almost agreed results from Monte Carlo calculations with the PHITS code. It was confirmed from radioactivecesium measurement on fly ash that the subtraction of energy spectral data of background radiations was useful for low-level radioactive-cesium measurement.