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Preliminary application of low-background gamma-spectrometry to volcanic ground water

Low-levels of 7Be, 22Na, 137Cs and radium isotopes as new geochemical tracers in a ground water flow system

Journal of Radioanalytical and Nuclear Chemistry
Authors:
M. Inoue
and
K. Komura

Abstract  

To enrich cosmogenic 7Be and 22Na, artificial 137Cs and natural radium isotopes, three chemical methods were applied to large volumes (100–300 l) of ground water from Daisen Volcano, Japan. The co-precipitation method using BaSO4, Fe(OH)3 and AMP, yielded 7Be, 137Cs and radium isotope levels of nearly 100%. An ordinary ion-exchange column method, selectively recovered 22Na (77%) through two continuous column operations. 40K was satisfactorily removed in both, the co-precipitation and column methods. In addition, the simple batch method was suitable for rapid treatment even on the slope of a volcano without sacrificing yields. Low-background γ-spectrometry combined with these chemical treatments enabled the determination of extremely low-levels of 7Be, 22Na, 137Cs and radium isotopes (0.01–4 mBq/l) in ground water samples. The measurement of these nuclides of Daisen ground water provide new information on the flow system of volcanic water, including residence time, the mixing of precipitation, and the aquifer’s environment.

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Abstract  

The temporal variation of 14C concentrations in atmospheric CO2 samples collected every 10 days was measured in the Takao area of Kanazawa, Ishikawa prefecture, Japan (36.52°N, 136.64°E), from April 1991 to December 1995. The monthly mean levels of 14C concentration in the Takao area demonstrated 10–50‰ lower concentrations than the background levels only in the winter season. This decrease seemed to be caused by the local fossil fuel contribution by heating in the winter season in the Takao area, which is located in an urban region near the center of Kanazawa. It is noteworthy that a remarkable peak was observed from late April to mid-May each year from 1991 to 1995 in the variation of 14C concentrations in atmospheric CO2. This phenomenon is similar to that of the so-called “spring peak” observed in Japan for other radionuclides.

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Abstract  

The long-term variation of 14C concentrations in atmospheric CO2 samples collected every 10 days was measured in the Ohkuwa area of Kanazawa, Ishikawa prefecture, Japan (36.3°N, 136.4°E), from April 1991 to December 2000. The 14C concentration decreased gradually by about 5‰ each year from 1991 to 2000, with a pronounced seasonal cycle which began to increase from spring and reached the maximum in late July or early August, followed by a decrease to the minimum from December to February. The appearance of large seasonal cycles and the extreme decrease of 14C concentration in winter seemed to be caused mainly by the air containing a large amount of 14C-free fossil fuel CO2 transported across the Sea of Japan from the Asian continent, not by the influence of local fossil fuel consumption.

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Abstract  

Concentration of organically-bound tritium in the tree-ring cellulose of a pine tree grown in Shika-machi, Ishikawa prefecture, Japan (37.1°N, 136.5°E), was measured during the ring-years from 1949 to 1999. The results were compared with those of a pine tree grown in Tatsunokuchi-machi, Ishikawa prefecture, Japan (36.4°N, 136.5° E). The annual variation of tritium in tree rings demonstrated two differences between the Shika-machi tree and the Tatsunokuchi-machi tree. No secondary peak appeared in the period after the maximum peak of 1963 for the Shika-machi tree, while two peaks appeared in 1966 and 1970 for the Tatsunokuchi-machi tree. In addition, the height of the 1963 peak was 30% higher for the Shika-machi tree than for the Tatsunokuchi-machi tree. These differences are considered to be caused by the influence that the underground water in the root zone of the Tatsunokuchi-machi tree was strongly affected by water which was transported to the tree site from mountain regions as compared to the Shika-machi tree.

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Abstract  

Diet samples were collected by a duplicate portion study of Japanese adults in two districts, a newly-rising town and an established seaside village, of Ishikawa Prefecture, which faces the Sea of Japan. Uranium concentrations in a total of 80 diet samples were determined by -spectrometry after chemical separation. No marked differences between the two districts were found regarding characteristics of food consumption in thirteen categories and in daily intake of238U per person. The daily intake of238U per person ranged from 1.1 to 40 mBq with a geometric mean value of 9.6±2.1 mBq. The234U/238U activity ratios ranged from 0.7–1.5, with most being from 1.0–1.2. The internal dose estimation system (IDES) was completed with Japanese physical parameters and other parameters of ICRP Publication 30, and then the annaul effective dose equivalent was estimated as 3·10–7 Sv for238U in a Japanese adult.

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Abstract  

An analytical method was developed for the measurement of low-level 54Mn in soil sample by ultra low-background g-ray spectrometry after radiochemical separation. The method consists of decomposition of sample by a mixture of HNO3 and HF, dissolution by HNO3, precipitation as hydroxide, solvent extraction with diisopropyl ether and anion exchange. Finally, for purification of Mn it was precipitated as MnO2 by adding KClO3. 54Mn in the precipitate was measured by ultra low-background well-type Ge detector at Ogoya Underground Laboratory. Measurements of 54Mn using 30-200 g of soil samples from the JCO grounds were successfully performed by the present method. The minimum detectable activity of 54Mn was about 0.01 dpm (0.2 mBq) for a 7-day counting period.

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Abstract  

Low-energy photon spectrometry with -spectrometry was used to determine the environmental concentrations of low-level actinides and other nuclides, especially210Pb and210Po. The isotopic ratio of240Pu/239Pu was successfully determined by measuring Lx-ray/-ray counting ratio. A reliable method has been developed for the determination of extremely low-level237Np global fallout in environmental samples. The non-destructive determination by Ge-LEPS for natural210Pb in various samples (tobacco leaves, commercially available tobacco, etc.) was also carried out with the determination of210Po by -spectrometry using209Po as a yield tracer.

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Ultra-sensitive mass spectrometric and other methods applied to environmental problems

Extremely low background measurements of 137Cs in seawater samples using an underground facility (Ogoya)

Journal of Radioanalytical and Nuclear Chemistry
Authors:
K. Hirose
,
M. Aoyama
,
Y. Igarashi
, and
K. Komura

Summary  

137Cs concentrations in seawater collected in 2002 and archived samples collected in 1957 were determined by using an AMP precipitation method and γ -spectrometry. 137Cs concentrations in the present water columns (>0.2 Bq . m-3) were determined using sample volumes of around 10 liters by the AMP precipitation method and ground-level γ-spectrometry at the Meteorological Research Institute (MRI). Equipment at the Ogoya Underground Laboratory (OUL) is able to achieve very low radioactivity measurements. As a result, we were able to measure 137Cs concentrations in deep waters (100-1500 m) in 1957, of about 1 Bq . m-3 from a small volume (250 ml) of the archived samples. The high sensitive 137Cs measurements allow effectively using 137Cs as a tracer of water motion in the ocean.

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Abstract  

137Cs in seawater is one of the most powerful tracers of water motion. Large volumes of samples have been required for determination of 137Cs in seawater. This paper describes improvement of separation and purification processes of 137Cs in seawater, which includes purification of 137Cs using hexachloroplatinic acid in addition to ammonium phosphomolybdate (AMP) precipitation. As a result, we succeeded the 137Cs determination in seawater with a smaller sample volume of 10 liter by using ultra-low background gamma-spectrometry in the Ogoya underground facility. 137Cs detection limit was about 0.1 mBq (counting time: 106 s). This method is applied to determine 137Cs in small samples of the South Pacific deep waters.

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Abstract  

This paper gives the first data on239,240Pu and241Am in Chinese soils. Surface soil samples with a set of 0–5 cm and 5–20 cm depth were collected from Beijing, Taiyuan, Shijiazhuang and Jinang of China in 1990, and239,240Pu,241Am and137Cs, including naturally occurring radionuclides, in these samples were measured to evaluate their present levels and distributions. From these results, the average accumulated depositions were estimated roughly to be 24±13 MBq/km2 for239,240Pu, 10±5 MBq/km2 for241Am and 1.2±0.7 GBq/km2 for137Cs. The activity ratios of239,240Pu/137Cs and241Am/239,240Pu ranged from 0.016 to 0.026 with a mean value of 0.020±0.004 and 0.35 to 0.49 with a mean value of 0.43±0.05, respectively.

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