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L K Fifield - One of the best experts on this subject based on the ideXlab platform.

  • 236u and 239 240pu ratios from soils around an australian nuclear weapons test site
    Journal of Environmental Radioactivity, 2016
    Co-Authors: S G Tims, L K Fifield, Michaela B Froehlich, A Wallner, M De Cesare
    Abstract:

    Abstract The isotopes 236 U, 239 Pu and 240 Pu are present in surface soils as a result of global Fallout from nuclear weapons tests carried out in the 1950's and 1960's. These isotopes potentially constitute artificial tracers of recent soil erosion and sediment movement. Only Accelerator Mass Spectrometry has the requisite sensitivity to measure all three isotopes at these environmental levels. Coupled with its relatively high throughput capabilities, this makes it feasible to conduct studies of erosion across the geographical extent of the Australian continent. In the Australian context, however, global Fallout is not the only source of these isotopes. As part of its weapons development program the United Kingdom carried out a series of atmospheric and surface nuclear weapons tests at Maralinga, South Australia in 1956 and 1957. The tests have made a significant contribution to the Pu isotopic abundances present in the region around Maralinga and out to distances ∼1000 km, and impact on the assessment techniques used in the soil and sediment tracer studies. Quantification of the relative Fallout contribution derived from detonations at Maralinga is complicated owing to significant contamination around the test site from numerous nuclear weapons safety trials that were also carried out around the site. We show that 236 U can provide new information on the component of the Fallout that is derived from the local nuclear weapons tests, and highlight the potential of 236 U as a new Fallout tracer.

  • 137 cs 239 240 pu concentrations and the 240 pu 239 pu atom ratio in a sediment core from the sub aqueous delta of yangtze river estuary
    Journal of Environmental Radioactivity, 2011
    Co-Authors: Shaoming Pan, S G Tims, X Y Liu, L K Fifield
    Abstract:

    Abstract A sediment core collected from the sub-aqueous delta of the Yangtze River estuary was subjected to analyses of 137 Cs and plutonium (Pu) isotopes. The 137 Cs was measured using γ-spectrometry at the laboratories at the Nanjing University and Pu isotopes were determined with Accelerator Mass Spectrometry (AMS), measurements made at the Australian National University. The results show considerable structure in the depth concentration profiles of the 137 Cs and 239+240 Pu. The shape of the vertical 137 Cs distribution in the sediment core was similar to that of the Pu. The maximum 137 Cs and 239+240 Pu concentrations were 16.21 ± 0.95 mBq/g and 0.716 ± 0.030 mBq/g, respectively, and appear at same depth. The average 240 Pu/ 239 Pu atom ratio was 0.238 ± 0.007 in the sediment core, slightly higher than the average global Fallout value. The changes in the 240 Pu/ 239 Pu atom ratios in the sediment core indicate the presence of at least two different Pu sources, i.e., global Fallout and another source, most likely close-in Fallout from the Pacific Proving Grounds (PPG) in the Marshall Islands, and suggest the possibility that Pu isotopes are useful as a geochronological tool for coastal sediment studies. The 137 Cs and 239+240 Pu inventories were estimated to be 7100 ± 1200 Bq/m 2 and 407 ± 27 Bq/m 2 , respectively. Approximately 40% of the 239+240 Pu inventory originated from the PPG close-in Fallout and about 50% has derived from land-origin global Fallout transported to the estuary by the river. This study confirms that AMS is a useful tool to measure 240 Pu/ 239 Pu atom ratio and can provide valuable information on sedimentary processes in the coastal environment.

Costas E Synolakis - One of the best experts on this subject based on the ideXlab platform.

  • spatial and temporal heterogeneity of 134 cs and 137 cs in topsoil after the fukushima daiichi nuclear power plant accident and the importance of tsunami debris management
    Environmental Processes, 2019
    Co-Authors: S Foteinis, N Kallithrakaskontos, M Kolovou, M Nikolaki, G Takoudis, C Potiriadis, Vassilios Skanavis, Nikos Kalligeris, Christos Housiadas, Costas E Synolakis
    Abstract:

    We present measurements of 134Cs and 137Cs activity concentrations in topsoil from the greater area of the Fukushima Daiichi nuclear power plant (FDNPP) in the period 2011–2013. Fallout concentrations were determined by means of gamma-ray spectrometry, using high purity germanium (HPGe) detectors. Concentration measurements ranged up to tens of thousands Bq/kg in Fukushima and Miyagi, and less in Iwate Prefecture, indicative of the Fallout distribution following the accident. Samples collected from undisturbed topsoil yielded higher Fallout concentrations than those collected from ploughed/cultivated land, suggesting that soil agitation redistributed Fallouts deeper in the ground. Overall, areas affected by the tsunami yielded, in general, very low topsoil concentrations. This could be attributed to tsunami debris cleanup, and to the flattening and uprooting of vegetation, which also adsorbs and absorbs Fallouts, thus rendering these areas prone to soil erosion. Certain Fallout hotspots identified in the inundation zone might have resulted from debris pile-up during initial cleanup. This highlights the importance of comprehensive debris cleanup.

Zheng Jian - One of the best experts on this subject based on the ideXlab platform.

  • 240Pu/239Pu atom ratios in water columns from the North Pacific Oceanand Bering Sea: Transport of Pacific Proving Ground-derived Pu by Ocean Currents
    Elsevier, 2020
    Co-Authors: Yamada Masatoshi, Zheng Jian
    Abstract:

    Nuclear weapons tests were conducted at the Bikini and Enewetak Atolls in the Pacific Proving Grounds (PPG) in the Marshall Islands between 1946 and 1958. The 240Pu/239Pu atom ratios in seawater samples from the northern North Pacific Ocean and Bering Sea were determined to elucidate the temporal variability in 239+240Pu inventory, to identify their Pu sources and to propose the transport pathways of PPG-derived Pu into the studied area. Water column 239+240Pu inventory in the Bering Sea was lower than that reported for a comparable station in the Geochemical Ocean Sections Study, indicating that the Bering Sea inventory has been decreasing from 76.0 ± 3.0 Bq m-2 to 37.1 ± 0.9 Bq m-2 during the period from 1973 to 1988 at the average rate of 2.6 ± 0.2 Bq m-2 yr-1. The 240Pu/239Pu atom ratios in the water column ranged from 0.222 to 0.255 with a mean value of 0.235 ± 0.008 in the northern North Pacific Ocean and from 0.215 to 0.237 with a mean value of 0.224 ± 0.004 in the Bering Sea. The obtained 240Pu/239Pu atom ratios were clearly higher than the mean global stratospheric Fallout ratio of 0.18. These high atom ratios proved the existence of close-in tropospheric Fallout Pu from nuclear weapons testing at the PPG. The relative contribution of the global stratospheric Fallout and the PPG close-in Fallout were evaluated by using the two-end-member mixing model. The 239+240Pu inventories originating from the PPG close-in Fallout were calculated as 17.9 – 25.4 Bq m-2 in the northern North Pacific Ocean and 11.6 – 16.6 Bq m-2 in the Bering Sea, which corresponded to 38 – 54% and 31 – 45% of the total- 239+240Pu inventory in the water column in the northern North Pacific Ocean and Bering Sea, respectively. A significant amount of the PPG close-in Fallout Pu has been transported to the northern North Pacific Ocean and Bering Sea. The proposed transport pathway accounting for the high 240Pu/239Pu atom ratio in the Bering Sea water column is the transportation of PPG-derived Pu by the North Equatorial Current followed by the Kuroshio Current, Kuroshio Extension, North Pacific Current and subsequently the Alaska Current, and then the Alaskan Stream

  • Determination of Pu-239, 240 concentration and Pu-240/Pu-239 atom ratio in seawater using an isotope dilution sector field-inductively coupled plasma-mass spectrometry
    2019
    Co-Authors: Yamada Masatoshi, Zheng Jian
    Abstract:

    The plutonium isotopes, 239Pu and 240Pu, have been added to the surface ocean mainly as a consequence of global Fallout from atmospheric nuclear weapons testing, while a second source has been close-in Fallout from nuclear weapons testing at the Pacific Proving Grounds. Since the 240Pu/239Pu atom ratio depends on the specific weapons design and test yield, it is a powerful fingerprint to identify the sources of Pu in the ocean. The objectives of this study are to determine the 239Pu, 240Pu and 239+240Pu concentrations and 240Pu/239Pu atom ratios in seawater from the Indian Ocean and to discuss the transport processes of plutonium in the ocean. The 239Pu and 240Pu concentrations and 240Pu/239Pu atom ratios were measured with an isotope dilution sector field-inductively coupled plasma-mass spectrometer (SF-ICP-MS), which was equipped with a guard electrode to eliminate secondary discharge in the plasma and to enhance overall sensitivity. The atom ratios in water column from the Indian Ocean were significantly higher than the mean global Fallout ratio of 0.180. These high atom ratios proved the existence of close-in Fallout plutonium originating from the Pacific Proving Grounds. The Bikini close-in tropospheric Fallout Pu could be transported to the eastern Indian Ocean by ocean currents.European Winter Conference on Plasma Chemistry (EWCPS)201

  • Determination of short-lived 241Pu in environmental samples by inductively coupled plasma mass spectrometry
    2019
    Co-Authors: Zheng Jian, Tagami Keiko, Bu Wenting, Uchida Shigeo
    Abstract:

    Plutonium isotopes have been released into the environment mainly from the atmospheric nuclear weapons tests in last century, the discharges from nuclear fuel reprocessing facilities, and the nuclear accidents, such as the Chernobyl and the Fukushima Daiichi Nuclear Power Plant (FDNPP) accidents [1-3]. Accurate determination of Pu isotopic composition is important for the source identification of radioactive contamination in the environment since Pu isotopic composition is characteristic for various Pu sources. Among Pu isotopes (238Pu, 239Pu, 240Pu, and 241Pu) observed in the environment, the short-lived 241Pu (t1/2 = 14.4 y), a beta emitter, in a sensitive indicator for the identification of any new contamination of Pu isotopes resulted from nuclear power plant accident. For 241Pu originated from the global Fallout, the activity 241Pu in the environment is quite low due to the dacay with time. The activity ratio of 241Pu/239+240Pu is ca. 1.2 in 2011 for the global Fallout-sourced Pu isotopes. Therefore, higher activity ratio of 241Pu/239+240Pu in the environment will provide evidence of additional Pu input. Due to its short half life and beta emission, determination of 241Pu in environmental samples has been a great analytical challege. Conventional technique is the low level liquid scintillation counting, which requires tedious sample preparation and long measurement time (typically 13-24 h). In the past years, we have developed sensitive analytical method using inductively coupled plasma mass spectrometry for the determination of 241Pu in various environmental samples, such as atmospheric fallou material, marine sediments, seawater reference material [4-6]. In this work, we report the determination of 241Pu environmental samples, such as litter, soil and marine sediments collected in Fukushima Prefecture after the FDNPP accident in 2011. Fig. 1 shows the results of 241Pu activity in litter and surface soils collected in 20-30 km zone of the FDNPP, and in Cities of Mito, Kamagaya and Chiba. High activities of 241Pu ranging from 4.5 to 34.8 mBq/g were detected in samples of the J-Vilage surface soil (0-2 cm) of two litter samples. This finding of high 241Pu activities in environmental samples after the FDNPP accidnet provided evidence of the release of Pu isootpes from the accident.５th Asia-Pacific Symposium on Radiochemistry (APSORC 13

  • Sources, distributions and transport processes of Pu isotopes in NW Pacific margin
    2019
    Co-Authors: Zheng Jian, Yamada Masatoshi
    Abstract:

    Plutonium was introduced into the environment mainly from the Fallout of atmospheric nuclear weapons tests. Over the past years, we have made a systematic investigation on the distribution of Pu isotopes in the NW Pacific Ocean and its adjacent seas: the East China Sea, Okinawa Trough, the Japan Sea and the Okhotsk Sea. Based on the obtained 240Pu/239Pu ratio signature, we identified the wide presence of Bikini close-in Fallout Pu in the studied regions, which contributed to the excess Pu inventories. We proposed that the oceanic process is responsible for the wide presence of Bikini close-in Fallout Pu. Using a two Fallout end-member model, we resolved the relative contribution of Pu between global Fallout and close-in Fallout in sediments. We concluded that the contribution of Bikini close-in Fallout Pu ranged from 10 % to 60 % in the studied regions [1-5]. To verify our hypothesis on the oceanic process for the transport of Pu in the Pacific Ocean, we further investigated the Pu isotopic signature in seawater and settling particles in the western Northwest Pacific [6-7]. Three transport processes were identified to be responsible for the distribution and fate of Pu isotopes in the NW Pacific margin: (1) advective lateral transport of dissolved Pu from open ocean to ocean margin; (2) vertical transport of Pu isotopes via particle scavenging; and (3) the bottom layer lateral transport and redistribution of Pu isotopes. \n[1] Zheng & Yamada (2004) ES&T 38, 3498-3504. [2] Zheng &Yamada, (2005) Stoten 340, 199-211. [3] Wang & Yamada (2005) EPSL 233, 441-453. [4] Zheng & Yamada (2006) JRNC 267, 73-83. [5] Zheng & Yamada (2005) JEM 7, 792-797. [6] Yamada et al. (2007) JER 98, 274-284. [7] Zheng & Yamada (2006) ES&T 40, 4103-4108.Goldschmidt 200

  • Pu isotope ratio analysis by sector-field ICP-MS reveals contamination sources and transport mechanism in teh western northwest Pacific
    2019
    Co-Authors: Zheng Jian, Yamada Masatoshi
    Abstract:

    Plutonium was introduced into the environment mainly from the Fallout of atmospheric nuclear weapons tests. There has been an increasing interest to study the distribution of Pu and its isotopes in the western North Pacific Ocean due to the application potential for tracing oceanographic processes occurring in the region and the need for radiological assessment. Over the years, we developed highly sensitive analytical methods for ultra-trace analysis of Pu isotopes using sector-field ICP-MS combined with a high-efficiency sample introduction system (APEX-Q), which allowed the determination of Pu isotope ratio at femtogram levels in various marine samples (sediments, settling particles and seawater). We made a systematic investigation on the distribution of Pu isotopes in sediments in the NW Pacific Ocean and its adjacent seas. Based on the obtained 240Pu/239Pu ratio signature, we identified the wide presence of Bikini close-in Fallout Pu in the studied regions. We proposed that the oceanic process is responsible for the wide presence of Bikini close-in Fallout Pu. The contribution of Bikini close-in Fallout Pu ranged from 10 % to 60 % in the studied regions. To verify our hypothesis on the oceanic process for the transport of Pu in the Pacific Ocean, we further investigated the Pu isotopic signature in seawater and settling particles in the western Northwest Pacific. The water column vertical profile of 240Pu/239Pu atom ratios in Sagami Bay showed no notable variation from the surface to the bottom with an average value of 0.234. This atom ratio was significantly higher than the mean global Fallout ratio of 0.18, and was in good agreement with that observed in the underlying sediment column, proving again the existence of close-in Fallout Pu originating from the Pacific Proving Grounds (PPG). It was found that Pu isotopes from the two sources of global Fallout and close-in Fallout have been homogenized in the water column in the western Northwest Pacific margin during the past four decades. Pu scavenging process was studied by measuring Pu isotopes in settling particles because settling particles have been regarded as the primary means by which surface-introduced Pu is transported to the sediments. To the best of our knowledge, this is the first time that both Pu activity and Pu isotope ratio data have been obtained for settling particles in the Pacific Ocean. The 240Pu/239Pu atom ratios are quite constant; the change of total mass flux in the different seasons did not result in a variation of Pu atom ratios in settling particles. The high 240Pu/239Pu atom ratios (0.23-0.27) in settling particles confirmed that Pu from the PPG source in the central Pacific is transported toward the western Northwest Pacific. Three transport processes were identified to be responsible for the distribution and fate of Pu isotopes in the NW Pacific margin: (1) advective lateral transport of dissolved Pu from open ocean to ocean margin; (2) vertical transport of Pu isotopes via particle scavenging; and (3) the bottom layer lateral transport and redistribution of Pu isotopes.2008 Third Asia-Pacific Winter Conference on Plasma Spectrochemistr

B G Harvey - One of the best experts on this subject based on the ideXlab platform.

  • measurements of fission products from the fukushima daiichi incident in san francisco bay area air filters automobile filters rainwater and food
    Journal of Environmental Protection, 2014
    Co-Authors: A R Smith, K J Thomas, E B Norman, D L Hurley, Y D Chan, P V Guillaumon, B G Harvey
    Abstract:

    A variety of environmental media were analyzed for Fallout radionuclides resulting from the Fukushima nuclear accident by the Low Background Facility (LBF) at the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, CA. Monitoring activities in air and rainwater began soon after the onset of the March 11, 2011 tsunami and are reported here through the end of 2012. Observed Fallout isotopes include

  • measurements of fission products from the fukushima daiichi incident in san francisco bay area air filters automobile filters rainwater and food
    arXiv: Nuclear Experiment, 2013
    Co-Authors: A R Smith, K J Thomas, E B Norman, D L Hurley, Y D Chan, P V Guillaumon, B G Harvey
    Abstract:

    A variety of environmental media were analyzed for Fallout radionuclides resulting from the Fukushima nuclear accident by the Low Background Facility (LBF) at the Lawrence Berkeley National Laboratory (LBNL) in Berkeley, CA. Monitoring activities in air and rainwater began soon after the onset of the March 11, 2011 tsunami and are reported here through the end of 2012. Observed Fallout isotopes include $^{131}$I, $^{132}$I,$^{132}$Te,$^{134}$Cs, $^{136}$Cs, and $^{137}$Cs. Isotopes were measured on environmental air filters, automobile filters, and in rainwater. An additional analysis of rainwater in search of $^{90}$Sr is also presented. Last, a series of food measurements conducted in September of 2013 are included due to extended media concerns of $^{134, 137}$Cs in fish. Similar measurements of Fallout from the Chernobyl disaster at LBNL, previously unpublished publicly, are also presented here as a comparison with the Fukushima incident. All measurements presented also include natural radionuclides found in the environment to provide a basis for comparison.

Yamada Masatoshi - One of the best experts on this subject based on the ideXlab platform.

  • 240Pu/239Pu atom ratios in water columns from the North Pacific Oceanand Bering Sea: Transport of Pacific Proving Ground-derived Pu by Ocean Currents
    Elsevier, 2020
    Co-Authors: Yamada Masatoshi, Zheng Jian
    Abstract:

    Nuclear weapons tests were conducted at the Bikini and Enewetak Atolls in the Pacific Proving Grounds (PPG) in the Marshall Islands between 1946 and 1958. The 240Pu/239Pu atom ratios in seawater samples from the northern North Pacific Ocean and Bering Sea were determined to elucidate the temporal variability in 239+240Pu inventory, to identify their Pu sources and to propose the transport pathways of PPG-derived Pu into the studied area. Water column 239+240Pu inventory in the Bering Sea was lower than that reported for a comparable station in the Geochemical Ocean Sections Study, indicating that the Bering Sea inventory has been decreasing from 76.0 ± 3.0 Bq m-2 to 37.1 ± 0.9 Bq m-2 during the period from 1973 to 1988 at the average rate of 2.6 ± 0.2 Bq m-2 yr-1. The 240Pu/239Pu atom ratios in the water column ranged from 0.222 to 0.255 with a mean value of 0.235 ± 0.008 in the northern North Pacific Ocean and from 0.215 to 0.237 with a mean value of 0.224 ± 0.004 in the Bering Sea. The obtained 240Pu/239Pu atom ratios were clearly higher than the mean global stratospheric Fallout ratio of 0.18. These high atom ratios proved the existence of close-in tropospheric Fallout Pu from nuclear weapons testing at the PPG. The relative contribution of the global stratospheric Fallout and the PPG close-in Fallout were evaluated by using the two-end-member mixing model. The 239+240Pu inventories originating from the PPG close-in Fallout were calculated as 17.9 – 25.4 Bq m-2 in the northern North Pacific Ocean and 11.6 – 16.6 Bq m-2 in the Bering Sea, which corresponded to 38 – 54% and 31 – 45% of the total- 239+240Pu inventory in the water column in the northern North Pacific Ocean and Bering Sea, respectively. A significant amount of the PPG close-in Fallout Pu has been transported to the northern North Pacific Ocean and Bering Sea. The proposed transport pathway accounting for the high 240Pu/239Pu atom ratio in the Bering Sea water column is the transportation of PPG-derived Pu by the North Equatorial Current followed by the Kuroshio Current, Kuroshio Extension, North Pacific Current and subsequently the Alaska Current, and then the Alaskan Stream

  • Determination of Pu-239, 240 concentration and Pu-240/Pu-239 atom ratio in seawater using an isotope dilution sector field-inductively coupled plasma-mass spectrometry
    2019
    Co-Authors: Yamada Masatoshi, Zheng Jian
    Abstract:

    The plutonium isotopes, 239Pu and 240Pu, have been added to the surface ocean mainly as a consequence of global Fallout from atmospheric nuclear weapons testing, while a second source has been close-in Fallout from nuclear weapons testing at the Pacific Proving Grounds. Since the 240Pu/239Pu atom ratio depends on the specific weapons design and test yield, it is a powerful fingerprint to identify the sources of Pu in the ocean. The objectives of this study are to determine the 239Pu, 240Pu and 239+240Pu concentrations and 240Pu/239Pu atom ratios in seawater from the Indian Ocean and to discuss the transport processes of plutonium in the ocean. The 239Pu and 240Pu concentrations and 240Pu/239Pu atom ratios were measured with an isotope dilution sector field-inductively coupled plasma-mass spectrometer (SF-ICP-MS), which was equipped with a guard electrode to eliminate secondary discharge in the plasma and to enhance overall sensitivity. The atom ratios in water column from the Indian Ocean were significantly higher than the mean global Fallout ratio of 0.180. These high atom ratios proved the existence of close-in Fallout plutonium originating from the Pacific Proving Grounds. The Bikini close-in tropospheric Fallout Pu could be transported to the eastern Indian Ocean by ocean currents.European Winter Conference on Plasma Chemistry (EWCPS)201

  • Sources, distributions and transport processes of Pu isotopes in NW Pacific margin
    2019
    Co-Authors: Zheng Jian, Yamada Masatoshi
    Abstract:

    Plutonium was introduced into the environment mainly from the Fallout of atmospheric nuclear weapons tests. Over the past years, we have made a systematic investigation on the distribution of Pu isotopes in the NW Pacific Ocean and its adjacent seas: the East China Sea, Okinawa Trough, the Japan Sea and the Okhotsk Sea. Based on the obtained 240Pu/239Pu ratio signature, we identified the wide presence of Bikini close-in Fallout Pu in the studied regions, which contributed to the excess Pu inventories. We proposed that the oceanic process is responsible for the wide presence of Bikini close-in Fallout Pu. Using a two Fallout end-member model, we resolved the relative contribution of Pu between global Fallout and close-in Fallout in sediments. We concluded that the contribution of Bikini close-in Fallout Pu ranged from 10 % to 60 % in the studied regions [1-5]. To verify our hypothesis on the oceanic process for the transport of Pu in the Pacific Ocean, we further investigated the Pu isotopic signature in seawater and settling particles in the western Northwest Pacific [6-7]. Three transport processes were identified to be responsible for the distribution and fate of Pu isotopes in the NW Pacific margin: (1) advective lateral transport of dissolved Pu from open ocean to ocean margin; (2) vertical transport of Pu isotopes via particle scavenging; and (3) the bottom layer lateral transport and redistribution of Pu isotopes. \n[1] Zheng & Yamada (2004) ES&T 38, 3498-3504. [2] Zheng &Yamada, (2005) Stoten 340, 199-211. [3] Wang & Yamada (2005) EPSL 233, 441-453. [4] Zheng & Yamada (2006) JRNC 267, 73-83. [5] Zheng & Yamada (2005) JEM 7, 792-797. [6] Yamada et al. (2007) JER 98, 274-284. [7] Zheng & Yamada (2006) ES&T 40, 4103-4108.Goldschmidt 200

  • Pu isotope ratio analysis by sector-field ICP-MS reveals contamination sources and transport mechanism in teh western northwest Pacific
    2019
    Co-Authors: Zheng Jian, Yamada Masatoshi
    Abstract:

    Plutonium was introduced into the environment mainly from the Fallout of atmospheric nuclear weapons tests. There has been an increasing interest to study the distribution of Pu and its isotopes in the western North Pacific Ocean due to the application potential for tracing oceanographic processes occurring in the region and the need for radiological assessment. Over the years, we developed highly sensitive analytical methods for ultra-trace analysis of Pu isotopes using sector-field ICP-MS combined with a high-efficiency sample introduction system (APEX-Q), which allowed the determination of Pu isotope ratio at femtogram levels in various marine samples (sediments, settling particles and seawater). We made a systematic investigation on the distribution of Pu isotopes in sediments in the NW Pacific Ocean and its adjacent seas. Based on the obtained 240Pu/239Pu ratio signature, we identified the wide presence of Bikini close-in Fallout Pu in the studied regions. We proposed that the oceanic process is responsible for the wide presence of Bikini close-in Fallout Pu. The contribution of Bikini close-in Fallout Pu ranged from 10 % to 60 % in the studied regions. To verify our hypothesis on the oceanic process for the transport of Pu in the Pacific Ocean, we further investigated the Pu isotopic signature in seawater and settling particles in the western Northwest Pacific. The water column vertical profile of 240Pu/239Pu atom ratios in Sagami Bay showed no notable variation from the surface to the bottom with an average value of 0.234. This atom ratio was significantly higher than the mean global Fallout ratio of 0.18, and was in good agreement with that observed in the underlying sediment column, proving again the existence of close-in Fallout Pu originating from the Pacific Proving Grounds (PPG). It was found that Pu isotopes from the two sources of global Fallout and close-in Fallout have been homogenized in the water column in the western Northwest Pacific margin during the past four decades. Pu scavenging process was studied by measuring Pu isotopes in settling particles because settling particles have been regarded as the primary means by which surface-introduced Pu is transported to the sediments. To the best of our knowledge, this is the first time that both Pu activity and Pu isotope ratio data have been obtained for settling particles in the Pacific Ocean. The 240Pu/239Pu atom ratios are quite constant; the change of total mass flux in the different seasons did not result in a variation of Pu atom ratios in settling particles. The high 240Pu/239Pu atom ratios (0.23-0.27) in settling particles confirmed that Pu from the PPG source in the central Pacific is transported toward the western Northwest Pacific. Three transport processes were identified to be responsible for the distribution and fate of Pu isotopes in the NW Pacific margin: (1) advective lateral transport of dissolved Pu from open ocean to ocean margin; (2) vertical transport of Pu isotopes via particle scavenging; and (3) the bottom layer lateral transport and redistribution of Pu isotopes.2008 Third Asia-Pacific Winter Conference on Plasma Spectrochemistr

  • The isotopic signature of plutonium in sediments from the western North Pacific margin
    2019
    Co-Authors: Zheng Jian, Yamada Masatoshi
    Abstract:

    Information on Pu isotopic compositions in sediments is very useful in understanding the source of Pu present there since the 240Pu/239Pu ratio has proved to be a powerful fingerprint to identify the Pu contamination. The atomic ratio of 240Pu/230Pu in Fallout may vary, depending upon the specific weapon design and test yield. The global Fallout average 240Pu/239Pu atom ratio is 0.18, based upon atmospheric aerosol sampling, soil samples and ice core data. It is also recognized that different test series can be characterized by either lower or higher ratios. For example, Fallout from the Nevada test site has a lower 240Pu/239Pu ratio, averaging 0.035, while elevated 240Pu/239Pu ratios (0.21-0.36) in Fallout from the 1950s from the Pacific Proving Grounds were reported. Recently, we have developed a highly sensitive method for the determination of 240Pu and 239Pu in marine sediment samples by means of ICP-MS (inductively coupled plasma mass spectrometry) with a shield torch system. In the present study, we have applied this method in order to determine 240Pu and 239Pu and their ratios in sediment core samples collected in Sagami Bay. Based on the 240Pu/239Pu ratio signature, we identified the additional Pu input in Sagami Bay was from the transported close-in Fallout from Bikini and Enewetak nuclear weapon tests. We demonstrate that Pu activity and isotopic ratio profiles of marine sediment cores contain records of global Fallout and close-in Fallout Pu, which provide chronological information on the recent sedimentation. We propose that the transport route is through the oceanic currents, e.g. the North Equatorial Current and Kuroshio Current. Using a two Fallout end-member model, we resolved the relative contribution of Pu between global Fallout and close-in Fallout in Sagami Bay sediments.International Workshop on Global Carbon Cycle and Related Mapping Based on Satellite Imagery and Climatic Chang