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  • Author or Editor: K. Komura x
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Abstract  

The carbon-14 concentration in tree-ring cellulose of an 80-year-old pine tree which has been used for tritium measurement was measured during the 1941–1987 period. This was done to determine the formation year of each tree ring in order to study the pathway of tritium uptake into the tree rings. In the 1941 to 1953 period, the Δ14C value remained slightly lower than 0%., It began to increase from 1954 to a small broad peak of 250% between 1959 and 1961, followed by rapid increase to the highest value of approximately 800% in 1964. Since 1964, it had been diminishing year by year to reach a level of 190% in 1987. The two peak years coincided with those in the known carbon-14 patterns in tree rings. However, there existed a difference in the amplitude of the Δ14C values during the period of 1963–1967.

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Abstract  

Uranium concentration and the 234U/238U activity ratio have been measured for the Tatsunokuchi hot spring waters of Ishikawa Prefecture in Japan, collected periodically over a long period (1977-2000). The concentration of 238U varied drastically between 0.045 and 1.02 mBq/l (a factor of about 20), while the 234U concentration was almost unchanged, ranging from 2.30 to 3.07 mBq/l. Resultant 234U/238U activity ratios showed a wide range from 2.7 to 51. Equilibrium calculation by using the geochemical code showed that U for one end-member representing low uranium contents and very high 234U/238U ratios was expected to exist as UO2(CO3)2 2-. By using the U isotopic and 14C dating methods, the age of this water was roughly estimated to be in the range of 104-105 years.

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Abstract  

A simple analytical method was developed for the determination of cosmogenic 22Na radionuclide in fresh water samples by ultra low-background g-ray spectrometry after radiochemical separation. The method consists in pre-concentration of 22Na(Na) by a ion exchange resin column from a large volume of ca. 500-liter water samples, elution with 4M HCl from the resin, and removal of the main metal components such as Ca and Mg as carbonate precipitates and of 40K(K) as potassium tetraphenylborate K[B(C6H5)4]. The obtained 22Na fraction was successfully measured by an ultra low-background Ge detector installed in the Ogoya Underground Laboratory.

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Abstract  

An analytical method has been developed for the determination of low-level99Tc in environmental samples by High Resolution ICP-MS. The method consists of leaching of99Tc by HNO3 and separation by three different solvent extractions with 30% TOA-xylene, MEK, and cyclohexanone. Finally, purification of99Tc was made by using an anion exchange resin column to reduce dissolved solids content. The final solution was adjusted to 1M HNO3 for introducing into the HR-ICP-MS. The accuracy and precision of the method was confirmed to be satisfactory by applying this technique to the determination of99Tc in IAEA marine algae sample (AG-B-1). Measurements of99Tc using 0.5–2.5 g of sediment samples from the Irish Sea, UK, were successfully performed by the present method.

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Abstract  

A neutron activation method based on the measurement of tritium radioactivity produced by6Li (n,)3H reaction was applied to determine the isotopic abundance of6Li in aqueous solution with known lithium concentration. Tritium radioactivity was measured with a low background liquid scintillation counter over a period of 2000 min. The present method demonstrated a good linearity between the isotopic abundance of6Li and tritium radioactivity produced per unit amount of lithium in a wide range of lithium concentration. A comparison of the present data with those from mass spectrometry showed agreement, though our method was 10 times less sensitive, than mass spectrometry. The present new approach should thus prove quite useful for determining the isotopic abundance of6Li.

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Abstract  

The fraction of labile hydrogens to total hydrogen atoms in cellulose isolated from a pine tree was found to be 10–11%. Most labile hydrogens in hydroxy groups of the cellulose could be eliminated within 6 h by heat treatment at 110°C with CuO in a flow of gas containing oxygen, due to dehydration of cellulose by interaction with oxygen which was accelerated by the presence of CuO. The contaminating effect of labile hydrogens on the measurement of tritium preserved in cellulose may thus be disregarded when such heat treatment is performed.

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Abstract  

In order to investigate the sedimentary behaviour of neptunium,237Np together with Pu isotopes and241Am have been measured for the sediment cores collected from Lake Mikata (freshwater) and from Lake Kugushi (brakish water) both belonging to the Mikata Five Lakes, and from Nyu Bay (sea water). In all sediment core samples237Np was detected, and its concentrations were far below those of239,240Pu and241Am measured for the same samples. Inventories of237Np in Lake Mikata, Lake Kugushi and Nyu Bay were estimated to be 0.53, 0.29 and 0.34 MBq/km2, respectively. The activity ratio of237Np/239,240Pu calculted from the inventories in each sediment core was 0.29% for Lake Mikata, 0.15% for Lake Kugushi and 0.10% for Nyu Bay. These values except for the value for Lake Mikata are two or three times lower than the value of 0.3–0.4% observed for surface soils of 0–20 cm depth, suggesting that Np is more soluble compared with Pu.

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Abstract  

Depth profiles and inventories of237Np in sediment cores from the Ribble Estuary in the Irish Sea have been studied along with those of Pu isotopes,241Am and137Cs, to allow a more detailed look of anomalously high237Np content observed in this estuary previously. The comprehensive data obtained showed that the depth profiles of both237Np contents and237Np/239,240Pu activity ratios were clearly different from those of239,240Pu,241Am, and137Cs and their activity ratios. As much as 80–90% of237Np inventories (0.32–1.06 kBq/m2), found in three cores, were estimated to be derived from a source other than Sellafield, on the basis of comparison of the237Np/239,240Pu inventory ratio (0.65–1.74%) found in the Ribble Estuary cores with those (0.10–0.16%) in the Ravenglass Estuary cores.

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Abstract  

The concentrations of210Po and210Pb were determined in about 30 species of marine organisms collected mainly from the north-easterm region of Japan to know the levels and distributions of these radionuclides and to estimate their intake levels from marine foods.210Po and210Pb showed a wide range of concentration in species: 0.6–26 and 0.04–0.54 Bq/kg (wet wt) in fishes, 0.5–220 and 0.2–43 Bq/kg (wet wt) in molluscs, echinoderms and chordatas, and 2.8–4.3 and 0.4–1.3 Bq/kg (wet wt) in algae, respectively. Higher accumulation of210Po relative to210Pb was found in all of the samples analyzed. The intake levels of210Po and210Pb by marine foods consumption were roughly estimated to be 0.48–0.69 and 0.022–0.042 Bq/d per person, respectively, on the basis of the statistical data on the consumption of seafood and/or production rates of marine foods.

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Abstract  

For determining low level lithium concentrations in water, a neutron activation method based on the measurement of tritium radioactivity produced by6Li(n,)3H reaction has been developed. This method is specific and free from interference by other chemical elements. Using a low background liquid scintillation counter for tritium measurement, the detection limit is approximately 0.3 ppm during irradiation at a thermal neutron flux density of 1.1·107n·cm–2·s–1 for 6 hours by a small nuclear reactor and liquid scintillation counting for 2000 minutes

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