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  • Author or Editor: T. Nakanishi x
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Abstract  

Cowpea (Vigna unguliculata Walp) is considered one of the most drought resistant species among the pulse crops. It was suggested that in the lower part of the stem, parenchymatous tissue for storing water has been developed for the function of drought resistance. However, such tissue has not been identified yet. In order to identify the water storing tissue in the stem of cowpea plant, the authors performed neutron radiography, which provides a non-destructive image of water distribution pattern in a plant. Common bean plant and soybean plant were used as references. Comparing the neutron radiograph for the stems of the plants, i.e., cowpea, common bean and soybean plants, the parenchymatous tissue with water storing function was distinguished in the intermode between primary leaf and the first trifoliate leaf specifically in cowpea plant.

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Abstract  

An analytical method for the determination of 239Pu and 240Pu in marine particle samples by sector field high-resolution ICP-MS was developed. The method was applied for large and small particle samples (particle diameter: >70 μm and 1–70 μm, respectively, collected with a large volume in situ filtration and concentration system at different depths in the water column off Rokkaho, Japan, where the spent nuclear fuel reprocessing plant of Japan Nuclear Fuel Ltd. has started test operation since March 2006.

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Abstract  

We have analyzed 16 elements and the radioactivity of 210Pb in a wood disk, across the annual rings to find out a promising tool for dendrochronology (chronology of wood) both for a Japanese wood, Cryptomeria japonica, and for an Indonesian rain forest wood, Alstonia, which does not form annual rings because of the relatively constant climate of the rain forest. As a result, only Mg concentration showed similar, smooth decreasing tendency in both wood species. The smooth change of the Mg concentration across the annual rings along with the growth suggested the possibility of the Mg concentration determination as a promising dendrochronological tool.

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Abstract  

We developed a quantitative, real-time imaging system of labeled compounds in a living plant. The system was composed of CsI scintillator to convert β-rays to visible light and an image intensifier unit (composed of GaAsP semiconductor and MCP; micro channel plate) to detect extremely weak light. When the sensitivity and resolution of the image of our system was compared with that of an imaging plate (IP), the sensitivity of our system (with 20 minutes) was higher than that of an IP, with similar quality to that of an IP. Using this system, the translocation of 32P in a soybean plant tissue was shown in successive images.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: T. Mitsugashira, M. Hara, T. Ohtsuki, H. Yuki, K. Takamiya, Y. Kasamatsu, A. Shinohara, H. Kikunaga, and T. Nakanishi

Abstract  

The alpha-decay of a low energy isomer of 229Th at about 3.5 eV was sought by producing it through the (g,n) reaction on a 230Th target. Thorium isotopes in the reaction products were isolated and purified by anion exchange chromatography in a concentrated nitric acid medium to remove lanthanides fission products. The thorium fraction was further purified by samarium fluoride coprecipitation and the precipitate was mounted as a source for a-spectroscopy. Decaying a-signals were observed in the energy region that was expected for 229mTh, i.e., between 4.83 and 5.08 MeV. The half-life of the decaying component was determined from repeated experiments to be 13.9±3 hours.

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Abstract  

Fluorine-18 produced by the18O(p,n)18F reaction on18O-water has proved to be highly useful as a source for a slow positron beam. About 70 GBq of18F is produced routinely by an ultra-compact cyclotron. The18F formed in H2 18O target is sent through a fine pipe to the site of positron slowing-down, fixed on a small spot by adsorption or drying, and then placed close to the moderator foil. An automatic apparatus has been set up for the entire process including the recovery of H2 18O.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Y. Miyamoto, H. Haba, A. Kajikawa, K. Masumoto, T. Nakanishi, and K. Sakamoto

Abstract  

The effect of following interferences was quantitatively assessed in terms of interference factor by irradiating samples together with highly pure reagents at two reactor sites of diferent neutron spectra and fluxes for neutron activation analysis (NAA) and an electron LINAC for photon activation analysis (PAA). The interfering reactions studied are 91) fast neutron-induced reactions, (2) uranium fission (3) (n,γ) reactions of other target elements in NAA, and (4) reactions induced by secondary neutrons in PAA. Corrections for these interferences were successfully applied to the activation analysis of some geological reference rock samples and biological samples.

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Summary  

We present a new trial to measure real time water movement in a living plant using the positron emitting radionuclide, 15O. 15O was prepared by 14N(d,n)15O reaction and 10 ml of 15O labeled water (2 GBq) was supplied from the root of a soybean plant. To detect activity, an imaging plate (IP) as well as a BGO detector system were used. Since the half-life of 15O is extremely short, (T 1/2= 122 s), water uptake measurement was performed only for 20 minutes. In order to get [15O]waterimage, an IP was exposed to the plant for 1 minute for two times. Since the exposure to an IP requires dark condition, a BGO detector system was developed to measure [15O]waterunder light condition. A couple of BGO probes was set at the lowest stem and the gamma-rays (0.511 MeV) emitted from the radionuclide were measured through coincidence counting and compared with the radioactivity measured from an IP image. Using this system, we have found that the water uptake activity of the plant was drastically reduced under high humidity (99%) and dark condition.

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Abstract  

Plutonium 239,240 was measured using large-volume water samples from the North Pacific and its adjacent seas. The vertical profiles of239,240Pu show features that are similar to those reported in earlier papers with a subsurface maxima of around 660 m and a significant concentration increase in the North Pacific bottom waters. It became evident that the239,240Pu concentration in deep bottom water is proportional to the inventory of the nuclides in the overlying water column and that the appearent distribution ratios of the nuclides between deep-sea sediment and bottom water lie in a relatively narrow range of about 2×104 to 105, independent of sea area and warter depth. The latter implies that239,240Pu may follow a reversible-type partition process at a deep water/sediment interface. In order to substantiate this assumption, it is desirable to study the phenomenon for Pu as well as for other long-lived radionuclides, both artificial and natural. From this point of view, an analytical procedure for the successive determination of selected long-lived radionuclides was studied.

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Abstract  

We present the real-time RI imaging and analyzing system to study the kinetics of nutrient uptake manner in a living plant. The system allowed light condition for the up-ground part of the plant and continuous dark condition for the root part, therefore, light/dark cycles was set as 16/8 h. There was 9,000 lx of LED lights in an aluminum container where the plant was set. The container was shielded well so that there was no light leakage to damage highly sensitive CCD camera which detected beta-rays from the sample. With this system, RI imaging was able to perform for 6 days without damaging the activity of the plant.

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