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  • Author or Editor: M. Aoyama x
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Abstract  

The wet and dry deposition of gamma-emitting nuclides are presented for Tsukuba and eleven stations in Japan following the nuclear reactor accident at Chernobyl'. In Japan fallout from the reactor at Chernobyl' was first detected on May 3, 1986, a week after the accident. Abruptly high radioactive deposition, which mainly consists of131I,132I,103Ru,137Cs and134Cs, was observed in early May. The cumulative amount of131I,103Ru and137Cs in May at Tsukuba were 5854±838 Bq·m–2, 364±54 Bq·m–2 and 130±26 Bq·m–2 (decay was corrected to April 26), respectively. The monthly137Cs deposition in May corresponds to 2.5% of the cumulative137Cs deposition during the period from 1960 through 1982. Most of the Chernobyl' radioactivities, especially131I, are scavenged from the atmosphere by the wet removal process.

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Abstract  

Plutonium was determined in monthly atmospheric deposition samples from 2000 to the end of 2003 collected at Tsukuba, Japan, together with monthly thorium deposition. Monthly 239,240Pu and thorium depositions showed a typical seasonal variation with a maximum in spring. The 230Th/232Th activity ratios in the deposition samples differed from that of surface soils near Tsukuba. These results reveal that a significant part of the 239,240Pu deposition observed in Japan is attributable to resuspension of deposited plutonium originating from the East Asian continent deserts and arid areas.

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Abstract  

The present plutonium levels in the Pacific Ocean are summarized. The 239,240Pu concentrations in surface seawaters in the early 2000s were in the range of 1.5 to 9.2 mBq·m−3 in the North Pacific and 0.8 to 4.1 mBq·m−3 in the South Pacific. There is no marked difference of surface 239,240Pu distributions between the North and South Pacific subtropical gyres. The vertical profile of 239,240Pu in the South Pacific was the similar pattern to that in the North Pacific, which is controlled by biogeochemical processes. The 239,240Pu inventories (down to 2300 m) in the North Pacific are generally greater than that in the South Pacific, which reflects the geographical distribution of global fallout and effect of close-in fallout in the Marshall Islands.

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Abstract  

Concentrations of cesium isotopes and plutonium in river water samples in Japan, collected during the period from June 1985 to February 1987, have been measured. The total137Cs concentrations in the Japanese river waters ranged from 0.063 to 1.89 mBq·l–1. The portion of particulate137Cs to total was observed to be less than 10 to 35%. The total239,240Pu concentrations ranged from 0.56 to 1.93 Bq·l–1. Particulate239,240Pu occupied 13 to 95% of the total. After the Chernobyl fallout, elevated137Cs concentrations were observed in the Japanese river waters as well as the detection of134Cs, whereas there was no effect on the river plutonium from the Chernobyl fallout. The partition coefficients of137Cs and plutonium between suspended particulate and dissolved phases in the Japanese rivers were determined: from 1.0·104 to 3.2·105 and from 4.1·104 to 2.3·106 for137Cs and plutonium, respectively. The result suggests that these radionuclides, especially plutonium, are tightly associated with soil particles and/or suspended matter.

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Abstract  

To clarify environmental effects of the Chemobyl radionuclides, long-lived Chernobyl radioactivity (239,240Pu,238Pu,241Pu and90Sr) in deposition samples in May 1986 was measured at 11 stations in Japan. Temporal variation of weekly deposition of90Sr differed from that of volatile radionuclides such as131I and137Cs, which may reflect the released process at Chernobyl. On the other hand, the geographical distributions of the monthly deposition of long-lived radionuclides were similar to those of volatile radionuclides, in which maximum deposits of90Sr and plutonium were observed in Akita, a northwestern Japan Sea coast site of Honshu Island. Higher241Pu deposition in most of the stations, as well as high238Pu/239,240Pu activity ratios were observed. The241Pu/238Pu activity ratios in deposition samples were nearly equal to that in the total release, which is clear evidence that Chernobyl-derived plutonium was transported to Japan in May 1986 together with volatile radionuclides although the contribution of Chernobyl Pu was about three orders of magnitude lower than137Cs.

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Abstract  

We determined 137Cs concentrations in deep water samples of the subtropical gyre in the South Pacific collected during the BEAGLE2003 cruise. This was done at an underground facility to achieve extremely low background γ-spectrometry, and we, therefore, obtained reliable values of 137Cs activity in the deeper layers. 137Cs activity in the layers between 2000 and 4500 m ranged from 7 ± 4 mBq m−3 to 25 ± 11 mBq m−3. The inventory of 137Cs in the water column from 2000 m to the sea bottom was estimated to be 20 ± 8 Bq m−2 to 94 ± 41 Bq m−2 in this region.

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Abstract  

We have observed an anomalous90Sr deposition at the Meteorological Research Institute (MRI), Tsukuba, Japan during the fall of 1995. This anomalous90Sr deposition was confirmed by the re-analysis of the sample, the associated lowest137Cs/90Sr activity ratio and high r/s ratio, etc. We discuss the cause of this anomalous90Sr deposition and conclude that the anomalous90Sr may come from an accidental release of nuclear battery, etc.

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Gonadotropin-releasing hormone (GnRH) is a ten-amino acid peptide hormone that plays pivotal roles in reproduction in vertebrates and octopus. Recently, six GnRH forms (t-GnRH-3-8) and four GnRH receptor subtypes (Ci-GnRHR-1-4) were identified in the protochordate, Ciona intestinalis . In this study, we show the functional modulation of Ci-GnRHR-1 via heterodimerization with the orphan receptor subtype, Ci-GnRHR-4. The dimerization between Ci-GnRHR-1 and R-4 was detected by co-immunoprecipitation and immunoblot analysis. Binding assays confirmed the binding of t-GnRHs to Ci-GnRHR-1 but not to R-4, and verified no alternation in ligand-binding affinity between Ci-GnRHR-1 homodimer and Ci-GnRHR1&4 heterodimer. The heterodimer was found to stimulate the elevation of intracellular calcium, time-extension of ERK phosphorylation, and up-regulation of cell proliferation, all in a ligand specific manner, compared with the Ci-GnRHR-1 homodimer. In combination, these results indicated that Ci-GnRHR-4 is not an inactive receptor, but a modulatory factor for Ci-GnRHR-1 in C. intestinalis .

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Abstract  

Plutonium concentrations in seawater of the western North Pacific observed over the period from 1985 to 1997 are reported. In the 1990's, surface 239,240Pu concentrations in the western North Pacific were relatively homogeneous (around 3 mBq/m3), although surface 239,240Pu before the 1980's showed a latitudinal distribution with highs in mid-latitudes and lows in the Equatorial region. Temporal variations of surface 239,240Pu in three different sea areas were examined. In mid-latitudes (21°–35°N), surface 239,240Pu exponentially decreased with an apparent residence time of 9.9 years, whereas in the subtropical and Equatorial areas, decrease rates of surface 239,240Pu were slower than in mid-latitudes. The vertical profiles of 239,240Pu in mid-latitudes of the western North Pacific showed a surface minimum, a subsurface maximum and decreased with increasing depth. The water column inventory of 239,240Pu at the station (27°48'N, 130°44'E) was calculated to be 113 Bq/m2.

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Abstract  

Temporal and spatial variations of 137Cs activity in surface waters in the western North Pacific are examined along the 165°E transect. 137Cs in seawater of the western North Pacific has been introduced by global fallout originating from atmospheric nuclear weapons tests, which caused major fallout in the early 1960's. At this time 137Cs activities in the surface waters in mid latitudes of the North Pacific were 10–20 Bq·m-3. South of 30°N, 137Cs activity decreased gradually towards the south. The surface 137Cs activity was about 5 Bq·m-3 in the Equatorial region. In the 1970's, the difference in 137Cs activities in surface water between mid latitudes and the Equatorial region became smaller. The 137Cs activity in surface water at 40°N – Equatorial region was almost constant at the level of 1.7–3.7 Bq·m-3 in the late 1990's. In the Equatorial region, the 137Cs activity in surface water showed no temporal change except for radioactive decay over these four decades. The surface 137Cs level was 1.4–1.8 Bq·m-3 in the north subarctic region around 50°N in the late 1990's. The lower 137Cs activity may have been caused by deeper convection in this sea area and dilution by fresh water flux.

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