24Naによる高エネルギーγ線領域のディスクリミネーターレベルの決定法

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When oxygen is determined by a 14-MeV neutron activation method, the high energy γ-rays from 16N in the range 67 MeV are measured and in order to count only these from 16N, it is necessary to discriminate the, γ-ray portion below a certain energy level. Formerly this discriminatory level had been decided by an aid of mercury pulser. However, the pulse from such a pulser might not have the same form as that come from the γ-ray detector and this could introduce some uncertainties in the level, thus decided. As no γ-ray reference sources having a γ-ray spectrum in the range 36 MeV are commercially available, the authors have studied the determination of the discriminatory level by the use of 24Na which can be obtained by a bombardment of Al samples with neutrons from for the analysis. 24Na has a high energy γ-ray spectrum in the range 1.244.22 MeV for a well-type NaI (T1) crystal. This method seems to be favourable because of the simplicity and the remarkable reproducibility. The Al sample can be used repeatedly; it is not necessary to provide a new Al sample before experiment. Furthermore the use of a multi-channel pulse height analyser could be avoided. It has been also shown in this work that the response of a NaI (T1) crystal for γ-ray is quite linear until a high energy level.
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