核分裂生成物のγ線スペクトロメトリ, (VI)

円筒型Nal (Tl)シンチレータによる²³⁵U核分裂生成物のγ線シンチレーション・スペクトル(計算と実験)

抄録

The calculation of scintillation spectra for the broad parallel γ rays emitted from ²³⁵U fission products incident on right circular Cylindrical Nal (Tl) crystals was presented. The detection efficiencies and photofractions of crystals were both taken from Miller, Reynold and Snow's works (1958). The procedures of the calculation were the same as those of the previous report (II). The typical figures of scintillation spectra from fission products were presented in both cases, one of which includes Compton continuum and the other does not. The parameters of the spectra were tabulated as functions of time after fission. The calculated spectra with a 1-3/4in. φ×1 in. crystal were practically same as those with the well type crystal which were referred in previous report (II). With a 4in. φ×4 in. crystal, however, the relative height of peaks in lower energy range, I, II and III, became lower whereas peak in higher energy range, X, became higher than those with a well type crystal. In another words all peaks tend to be equalized in relative height for larger crystals.
The samples of fission products, of which the data were presented in previous report (III), were measured with a 1-3/4in. φ×1 in. Nal (Tl) crystal and with 1 in. φ×1 in. anthracene crystal by both conventional and two-crystal scintillation spectrometers. In the latter, Compton continuum was automatically subtracted on recorded spectra. In general, the resolution of cylindrical crystals was better than that of well type, and so the more detailed structures were observable in the scintillation spectra with cylindrical crystals. Accordingly, to deduce the ages of fission products, the former was more useful than the latter.
Comparison of the experimentals with the calculated spectra shows a good agreement except at the peak I, II and V. The cause of said discrepancy was alraedy discussed in the previous report (III). In addition, the calculated spectrum was compared with other experimental spectrum. Although the conditions of the experiments were not always equal to the assumption for the calculation, there showed a rather good agreement between both spectra.