RADIOISOTOPES

The CO₂-laser-induced, SF₆-sensitized decomposition of gaseous UF₆ is used to produce UF₅ fine particles with diameters far smaller than 1, um. The UF₅ particles are directly subjected to a-spectrometry with a high-resolution Si semiconductor detector for the determination of the ²³⁵U/²³⁸U isotopic ratio. Owing to the extremely small particle dimensions, self-absorption of α-energy is not serious and the ²³⁸U/²³⁵U/²³⁴U peaks are clearly resolved ; the spectral widths of respective isotopes for UF₅ particles are only 2.5 times broader than those for authentic U₃O₈ standard sources. Measurements of the ²³⁵U/²³⁸U ratio in natural UF₅ samples are found to be accurate to within 4%. This suggests that α-spectrometry can be used for the on-line analysis of enrichment factors in UF₅ products in the molecular laser isotope separation (MLIS) of uranium.

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Afterglow colour images (AGCI) and thermoluminescence (TL) from Japanese twin quartz slices have been successfully photographed by means of a commercially available negative colour film after the irradiation of X-rays. Afterglow colour images (AGCI) offered very interesting distinction of colour images ; the core part showed the colour changed from sky blue with zonal orange to blue with increasing absorbed doses, whereas the outer parts maintained orange AG colour giving clear boundary. On the other hand, the radiation-induced colour (blackish or brownish) center image (CCI) appeared at the core portion, while thermoluminescence colour images (TLCI) also consisted of two portions distinguishable into stripe and tonal bluish core and faint TL emission part in outer ones. These luminescence colour images, probably reflecting the formation mechanism of Japanese twin quartzes, are evidently correlated with the concentration patterns of aluminium impurity obtained by an EPMA (electron probe microanalyzer) method. From these radiation-induced images, it was assumed that the conditions of crystal formation should be greatly different between the core and the outer parts; the outer parts were secondarily started to grow from hydrothermal solution with higher Al-concentration after the initial formation of single core.

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Distribution of radioactivity in Hokutolite from Hokuto hot spring, Taiwan was examined by using an imaging analyzer. The cut surface of the Hokutolite along the growing direction was contacted with an imaging plate and a two-dimensional radioactive distribution including an underlying rock part was obtained. The image processed by a computer represents a heterogeneous distribution of radioactivity in Hokutolite due to incorporation of non-radioactive rocks and fine particles during its growing from hot spring water. Lower radioactivity had been expected for the part of Hokutolite near the underlying rock than that at the surface of the Hokutolite because of older age. However, we could not confirm such a decline of the radioactivity from the surface toward the deeper part of the Hokutolite.

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