We have reported previously on the radiation-induced formation of highly fluorescent products from thymine, cytosine, adenine, 2''-deoxyadenosine, and 2''-deoxyguanosine. For comparison with these substances, 2''-deoxycytidine (5.0 × 10^-4 mol/dm³) and cytidilyl-cytidine (2.5 × 10^-4 mol/dm³) in buffered aqueous solution (pH 7.0) were irradiated with ⁶⁰Co gamma-rays under various atmospheric conditions. Fluorescence yield increased markedly with increase of radiation dose under O₂, N₂ and N₂O but not under t-butanol-N₂, indicating that OH radical is the predominant participant in the formation of highly fluorescent products and that 0₂ does not suppress the yield. These behaviors are very similar to those for cytosine. However, the fluorescent products from 2''-deoxycytidine and cytidilyl-cytidine were radiolytically more stable than those from cytosine. To summarize the formation of highly fluorescent products from various kinds of nucleobase derivatives by radiatioh, the order for fluorescence yield can be arranged as follows: C > A > G >T under O₂, A >G > C >T under N₂O, and G >>A >> C > T under t-butanol-N₂, excepting the complex yield under N₂.

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The conversion of atmospheric molecular tritium (HT) to tritiated water in soils was examined. The oxidation rate of HT varied with soil depth, temperature and soil water content. Among three sandy loam soils, rate constant was highest in the top section (0-5 cm) of grassy forest soil, 0.196/min, and in lower sections with soil depths of 5 to 10 cm and 10 to 15 cm, the rate constants were one fourth and one eighth, respectively, of that of the top section. The rate constants of the top sections of paddy and upland fields were 0.038/min and 0.058/min. Oxidation occurred over a broad temperature range from 0 to 75°C. Optimal water content for HT oxidation ranged from 10 to 25% of soil dry weight. The addition of KCN or NaN₃ to the soil partially decreased HT oxidation and pretreatment with chloroform or acetone (20%) reduced the oxidation rate by a half. HT oxidation activity in the surface soil (0-5 cm) under anaerobic conditions was somewhat less than that under aerobic conditions, but below this depth, the activity was essentially the same under either condition.

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The contents of ⁹⁰Sr and ¹³⁷Cs in two samples of Japanese cedar from Takao and Tsukui districts were determined in tree rings cut into segments representing steps of 5 years of growth. ⁹⁰Sr in both cedar samples and ¹³⁷Cs in the Tsukui cedar sample were determined after ashing and chemical isolation, while ¹³⁷Cs in the Takao sample was directly determined from the sample ash. The distribution of ⁹⁰Sr fallout in tree rings suggests that ⁹⁰Sr had given a rather direct effect and showed no significant translocation from sapwood to heartwood, whereas ¹³⁷Cs tends to concentrate in heartwood irrespective of the effect of the fallout. Average contents of ⁹⁰Sr and ¹³⁷Cs were 22 and 9.4 pCi/kg in the Takao sample (9.61 kg air dried) and were 23 and 12 in the Tsukui (4.71 kg air dried) in 1982.

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