17 Mev 竝に 6.1 Mev γ線の二,三物質による吸收係数の測定

Abstract

The γ-ray absorption coefficients of Pb, Sn, Cu, and Al were measured for the 17.6 Mev and 6.1 Mev γ-rays produced at the first proton resonance of the (Li-p) and (F-p) reactions respectively. The experimental arrangement used is shown in Fig. 1. In order to obtain the homogeneity of γ-rays, a filter to absorb the x-rays from the target by proton bombardment was not used near the target and each sample used had a diameter which was enough to cover the outside of the canalizing lead slit. Therefore, to detect the γ-rays, a thick lead plate was used in front of the window of the G-M counter of end-window type. The thickness of the plate was 7.5mm and 5.9mm for the 17.6 Mev and 6.1 Mev γ-rays respectively. To exclude the stray radiation, a set of canalizing lead slit and plug was placed upon the lead counter which was housed in a large lead box. Then the difference of counts with and without the lead plug for each sample is taken to be the true decrement of the γ-rays through the canal due to the absorption by the substance. Furthermore, in order to monitor the γ-ray intensity, a 6.5 mm lead counter shielded by a lead cylinder was placed in such a position that suffers no effect by the conditions of the sample. The absorption coefficients obtained under these conditions are given as follows: [Table omitted] Analysing these experimental data, the absorption due to the creation of electron pairs seems to be proportional to Z2 in the case of the 17.6 Mev γ-rays. However, it is to be noted that the absorption coefficient of Al for the 17.6 Mev γ-rays is found to be larger than the theoretical value.