RADIOISOTOPES

In the fission track method, the counting of fission track is performed with the naked eye using a microscope, and the researcher experiences intense eye strain when examining a large number of samples. As a result, counting errors are more likely to occur, requiring more time to complete the work. The present study has been undertaken with the aim of increasing the accuracy and efficiency of track counting in order to solve the above-mentioned problems associated with the fission track method. The following conclusions were obtained.
1. The accuracy of track counting in the fission track method can be improved by introducing photomicrography to the conventional method of track counting with the naked eye.
2. A digital counter that displays track numbers automatically has been made, but it requires further improvement of accuracy for practical application.

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The distribution coefficients of radon in water: air phase and organic solvents: air phase have been determined by means of gamma-ray spectrometry and liquid-scintillation alpha-ray spectrometry. Radon partitioning between two phases has been performed using a separatory funnel. The distribution coefficients of radon between water: air phase, toluene: air phase and mixed-xylene: air phase at 20°C and p-xylene: air phase at 17°C were obtained to be 0.264±0.007, 13.3±0.8, 14.5± 0.8 and 15.7±0.9, respectively. The distribution of radon into three phases (water, organic solvent and air phase) has been also investigated and the results were in agreement with those of two-phase experiments.

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The measurement system for Doppler broadening profiles with the coincidence technique using a NaI detector in colinear geometry with a Ge detector was developed. The principle of measurement system with the coincidence technique between the NaI detector and the Ge detector was described. Application of the system for the detection of vacancy-type defects introduced by electron irradiation in Czochralski- (Cz) grown Si was shown. Detail in the difference between the Doppler broadening profiles for Cz-Si and Si grown by the floating-zone method was also obtained.

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The concentrations of ¹³⁷Cs in water, sediment and fishes at the pond in Saitama prefecture were determined in order to elucidate the radioecology of ¹³⁷Cs in limnological ecosystems.
¹³⁷Cs concentration in water was 0.31±0.002 mBq/l (mean±standard error), and so indicated about 3 times higher than that (0.10mBq/l) for the river in our previous report. ¹³⁷Cs concentrations in sediment, carp, Cyprinus carpio, crucian carp, Carassius auratus cuvieri, and Hakuren, Hypophthalmichthys molitrix, were about 20000, 1200, 2 400 and 3100 times higher than that of the water, respectively. These concentrations were higher than those of each sample for the river in our previous report. It was so suggested that¹³⁷ Cs tended to be accumulated in these samples at the pond more than the nuclide in the river.
Moreover, concentration ratios, concentration of¹³⁷Cs in sediment, crucian carp and Hakuren to that of the water, were about 30, 2 and 3 times higher than these of ⁴⁰K, respectively, except for carp of which ¹³⁷Cs and⁴⁰K concentration ratios were almost same.
These results showed difference in accumulation mechanism between¹³⁷Cs and⁴⁰K in these samples, as well as¹³⁷Cs transfer mechanism in the limnological ecosystems in part.

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