ガンマ線ピーク効率測定におけるサム効果と測定高さの関係

抄録

In the measurement of environmental radioactivities by Ge detector, the calibration curve of the full-energy peak efficiencies needs to be obtained from standard γ-ray sources. When high energy γ-ray emitters viz., ⁶⁰Co or ⁸⁸Y are used as standard sources, the correction of coincidental summing effects is necessary for estimating true peak efficiencies. It, however, requires complicated calculations and a simpler way to obtain the ralibration curve has been desired very much.
It is well known that the more the distance between a counting sample and a detector endcap is, the less becomes the summing effect, though the efficiency of the measurements may increase. This interrelation, however, seemed still indistinct and the present paper intended to find the optimum source distance to minimize the measurement error and the summing effects without the complicated calculation for the correction.
The results indicates that the error of the measurements can be practically low enough without the correction of coincidental summing effects for our detecting system, when the source distance from the detector endcap is about 3 cm.