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The opportunity to measure the concentrations of 3 H and 36 Cl released by the Fukushima nuclear accident in 2011 directly in rain was lost in the early stage of the accident. We have, however, been able to reconstruct the deposition record of atmospheric 3 H and 36 Cl following the accident using a bore hole that was drilled in 2014 at Koriyama at a distance of 60 km from the accident. The contributions of 3 H and 36 Cl from the accident are 1.4 × 10 13 and 2.0 × 10 12 atoms m -2 respectively at this site. Very high concentrations of both 3 H (46 Bq L -1 ) and 36 Cl (3.36 × 10 11 atoms L -1 ) were found in the unsaturated soil at depths between 300 and 350 cm. From these, conservative estimates for the 3 H and 36 Cl concentrations in the precipitation in the ~ 6 weeks following the accident were 607 Bq L -1 and 4.74 × 10 10 atoms L -1 , respectively. A second hole drilled in 2016 showed that 3 H concentrations in the unsaturated soil and shallow groundwater had returned to close to natural levels, although the 36 Cl concentrations were still significantly elevated above natural levels., (© 2023. The Author(s).)

Concentrations of 127 I and 129 I in rainwater samples from several stations across Argentina (latitudes between 25° S and 55° S) were measured and analyzed for the assessment of distribution patterns and potential sources of 129 I in the Southern Hemisphere. Measured 129 I levels, clearly above those explainable by natural background and atmospheric nuclear weapons tests, can be understood by the injection into the Southern Hemisphere of 129 I that had been discharged from nuclear fuel reprocessing plants in the Northern Hemisphere., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Half of the chemical elements heavier than iron are produced by the rapid neutron capture process (r-process). The sites and yields of this process are disputed, with candidates including some types of supernovae (SNe) and mergers of neutron stars. We search for two isotopic signatures in a sample of Pacific Ocean crust-iron-60 ( 60 Fe) (half-life, 2.6 million years), which is predominantly produced in massive stars and ejected in supernova explosions, and plutonium-244 ( 244 Pu) (half-life, 80.6 million years), which is produced solely in r-process events. We detect two distinct influxes of 60 Fe to Earth in the last 10 million years and accompanying lower quantities of 244 Pu. The 244 Pu/ 60 Fe influx ratios are similar for both events. The 244 Pu influx is lower than expected if SNe dominate r-process nucleosynthesis, which implies some contribution from other sources., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Nuclides synthesized in massive stars are ejected into space via stellar winds and supernova explosions. The solar system (SS) moves through the interstellar medium and collects these nucleosynthesis products. One such product is 60 Fe, a radionuclide with a half-life of 2.6 My that is predominantly produced in massive stars and ejected in supernova explosions. Extraterrestrial 60 Fe has been found on Earth, suggesting close-by supernova explosions ∼2 to 3 and ∼6 Ma. Here, we report on the detection of a continuous interstellar 60 Fe influx on Earth over the past ∼33,000 y. This time period coincides with passage of our SS through such interstellar clouds, which have a significantly larger particle density compared to the local average interstellar medium embedding our SS for the past few million years. The interstellar 60 Fe was extracted from five deep-sea sediment samples and accelerator mass spectrometry was used for single-atom counting. The low number of 19 detected atoms indicates a continued but low influx of interstellar 60 Fe. The measured 60 Fe time profile over the 33 ky, obtained with a time resolution of about ±9 ky, does not seem to reflect any large changes in the interstellar particle density during Earth's passage through local interstellar clouds, which could be expected if the local cloud represented an isolated remnant of the most recent supernova ejecta that traversed the Earth ∼2 to 3 Ma. The identified 60 Fe influx may signal a late echo of some million-year-old supernovae with the 60 Fe-bearing dust particles still permeating the interstellar medium., Competing Interests: The authors declare no competing interest.

The Daly River drains a large (52500 km 2 ) and mainly undisturbed catchment in the Australian wet-dry tropics. The basin landscapes are mantled by a thick veneer of kandosol soil which has developed under varying rates of erosion, uplift, bedrock type and climate and has been identified as being suitable for agriculture. Commencement of large scale clearing and cropping since 2002 have raised concerns about the increased loss of top soil from the land clearing and cultivation activities adjacent to the Daly River. This study was undertaken to determine the modern soil loss rates which can be used to develop a sustainable soil conservation strategy for this catchment. 239 Pu, released in the 1950s and 1960s by atmospheric nuclear weapons tests, is used to obtain a quantitative assessment of recent rates of soil loss. Soil cores 30-40 cm deep have been collected from fields with various land uses including peanut and hay cropping and cattle grazing. Cores taken from undisturbed and unburnt areas in open eucalypt woodland have been used as reference sites. The soil loss rates have been established by comparing the excess or deficiency of the 239 Pu tracer over that of the reference sites. Since land use practices in the catchment are similar, it is likely that the measured soil loss rates are indicative of soil loss rates over the Daly Basin as well. The development of 239 Pu as a soil tracer represents a viable alternative to the traditionally used 137 Cs tracer. This also represents a new tool in the quantification of catchment soil loss and the adoption of appropriate soil conservation strategies for the tropical regions and regions where increasing settlement and agriculture are encroaching on catchment slopes., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Anthropogenic radionuclides, like 236 U and 239,240 Pu, are present in the environment as a result of global fallout from nuclear weapons tests conducted in the 1950s and 1960s and can potentially be used as tracers in soil erosion and sediment movement studies. Here, we report data on 236 U and 239,240 Pu in soil samples from the Motueka Valley (New Zealand) and for the first time from two remote islands Rarotonga and Atiu (Cook Islands) in the South Pacific. 236 U and 239,240 Pu were measured using Accelerator Mass Spectrometry (AMS) at the Australian National University. The 236 U and 239 Pu isotope concentrations versus soil depth and the 240 Pu/ 239 Pu and 236 U/ 239 Pu isotope ratios are discussed for each site. The radionuclide depth dependence revealed any soil disturbance, whereas the isotopic signatures indicated the source of the radionuclides' origin., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The 240 Pu/ 239 Pu atom ratio is a very effective tool for the identification of the origin of plutonium (Pu) in the soil environment. We examine a dataset of 240 Pu/ 239 Pu atom ratios determined from surface and core soils at 240 sites across China. The data were compiled from 18 separate literature sources from the last 20 years. For the first time the spatial distribution (3 latitude bands and 7 natural regions) of the weighted average 240 Pu/ 239 Pu atom ratios in Chinese soils is investigated. An area to the West of Xining City, shows a weighted average 240 Pu/ 239 Pu atom ratio of 0.167 ± 0.002, lower than that of average global fallout, which likely arises from the addition of local fallout radionuclides from the Chinese nuclear weapon tests at Lop Nor between 1964 and 1980. The Yumen and Jiuquan areas of Northwest China in particular show evidence of very low ratio material from the Chinese nuclear weapon tests. Excluding the impacted area around the test site the weighted average 240 Pu/ 239 Pu ratio of 0.182 ± 0.002 suggests that global fallout is the main source of Pu in most Chinese soils., (Crown Copyright © 2019. Published by Elsevier B.V. All rights reserved.)

We searched for the presence of ^{26}Al in deep-sea sediments as a signature of supernova influx. Our data show an exponential dependence of ^{26}Al with the sample age that is fully compatible with radioactive decay of terrigenic ^{26}Al. The same set of samples demonstrated a clear supernova ^{60}Fe signal between 1.7 and 3.2 Myr ago. Combining our ^{26}Al data with the recently reported ^{60}Fe data results in a lower limit of 0.18_{-0.08}^{+0.15} for the local interstellar ^{60}Fe/^{26}Al isotope ratio. It compares to most of the ratios deduced from nucleosynthesis models and is within the range of the observed average galactic ^{60}Fe/^{26}Al flux ratio of (0.15±0.05).

Based on AMS analysis, it is shown that no Pu signals from the Fukushima accident could be discerned in marine sediments collected 1.5-57km away from the Fukushima Da-ichi power plant (FDNPP), which were clearly influenced by accident-derived radiocesium. The 240 Pu/ 239 Pu atom ratios (0.21-0.28) were significantly higher than terrestrial global fallout (0.182 ± 0.005), but still in agreement with pre-FDNPP accident baseline data for Pu in near coastal seawaters influenced by global fallout and long-range transport of Pu from the Pacific Proving Grounds., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

At present there is a need for the development of new radioisotopes for soil erosion and sediment tracing especially as fallout 137 Cs levels become depleted. Recent studies have shown that 239 Pu can be a useful new soil erosion and sediment radioisotope tracer. 239 Pu was released in the major atmospheric nuclear weapons tests of 1950's and 1960's. However 239 Pu has a half-life of 24110 years and more than 99% of this isotope is still present in the environment today. In contrast 137 Cs with a half-life of 30.07 year has decayed to <35% of initially deposited activities and this isotope will become increasingly difficult to measure in the coming decades especially in the southern hemisphere, which received only about a third of the total global fallout from the atmospheric tests (UNSCEAR, 2000). In this study an assessment of the 239 Pu fallout in Australia was carried out from comparison of measured 239 Pu inventories with expected 239 Pu inventories from fallout models. 239 Pu inventories were also compared with rainfall and measured 240 Pu/ 239 Pu ratios across Australia. 239 Pu fallout inventories ranged from 430 to 1461 μB/cm 2 . Central Australia, with fallout 107% in excess of expected values, seems to be strongly impacted by local fallout deposition. In comparison other sites typically show 5-40% variation between expected and measured fallout values. The fallout inventories were found to weakly correlate (using power functions, y = ax b ) with rainfall with r 2  = 0.50 across the southern catchments (25-40°S latitude band). Across the northern catchments (10-25°S latitude band) fallout showed greater variability with rainfall with r 2  = 0.24. Central Australia and Alice Springs which seem to be strongly impacted by local fallout are excluded from the rainfall correlation data (with these sites included r 2  = 0.08 and r 2  < 0.01 respectively). 240 Pu/ 239 Pu atom ratios range from 0.045 to 0.197, with averages of 0.139(0.017), 0.111(0.052) and 0.160(0.027) in the 10-20°S, 20-30°S and 30-40°S latitude bands respectively. The 240 Pu/ 239 Pu atom ratios in Central Australia (0.069) likely represent fallout from the Australian tests which also have low 240 Pu/ 239 Pu atom ratios i.e., Maralinga (0.113) and Montebello (0.045). The average ratios in the 20-30°S and 30-40° bands are closer to the global average (0.139 and 0.177 respectively when not including the close-in fallout data from the nuclear test sites) if the Australian test sites and Central Australian sites are neglected as they clearly represent the effects of close in fallout., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A slice from a Porites Lutea coral core collected inside the Enewetak Atoll lagoon, within 15 km of all major nuclear tests conducted at the atoll, was analysed for 236 U, 239 Pu and 240 Pu over the time interval 1952-1964 using a higher time resolution than previously reported for a parallel slice from the same core. In addition two sediment samples from the Koa and Oak craters were analysed. The strong peaks in the concentrations of 236 U and 239 Pu in the testing years are confirmed to be considerably wider than the flushing time of the lagoon. This is likely due to the growth mechanism of the coral. Following the last test in 1958 atom concentrations of both 236 U and 239 Pu decreased from their peak values by more than 95% and showed a seasonal signal thereafter. Between 1959 and 1964 the weighted average of the 240 Pu/ 239 Pu atom ratio is 0.124 ± 0.008 which is similar to that in the lagoon sediments (0.129 ± 0.006) but quite distinct from the global fallout value of ∼0.18. This, and the high 239,240 Pu and 236 U concentrations in the sediments, provides clear evidence that the post-testing signal in the coral is dominated by remobilisation of the isotopes from the lagoon sediments rather than from global fallout., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Unusually high concentrations of americium and plutonium have been observed in a sediment core collected from the eastern Lombok Basin between Sumba and Sumbawa Islands in the Indonesian Archipelago. Gamma spectrometry and accelerator mass spectrometry data together with radiometric dating of the core provide a high-resolution record of ongoing deposition of anthropogenic radionuclides. A plutonium signature characteristic of the Pacific Proving Grounds (PPG) dominates in the first two decades after the start of the high yield atmospheric tests in 1950's. Approximately 40-70% of plutonium at this site in the post 1970 period originates from the PPG. This sediment record of transuranic isotopes deposition over the last 55 years provides evidence for the continuous long-distance transport of particle-reactive radionuclides from the Pacific Ocean towards the Indian Ocean.

A comprehensive series of nuclear tests were carried out by the United States at Enewetak Atoll in the Marshall Islands, especially between 1952 and 1958. A Porites Lutea coral that was growing in the Enewetak lagoon within a few km of all of the high-yield tests contains a continuous record of isotopes, which are of interest (e.g. 14 C, 236 U, 239,240 Pu) through the testing period. Prior to the present work, 14 C measurements at ∼2-month resolution had shown pronounced peaks in the Δ 14 C data that coincided with the times at which tests were conducted. Here we report measurements of 236 U and 239,240 Pu on the same coral using accelerator mass spectrometry, and again find prominent peaks in the concentrations of these isotopes that closely follow those in 14 C. Consistent with the 14 C data, the magnitudes of these peaks do not, however, correlate well with the explosive yields of the corresponding tests, indicating that smaller tests probably contributed disproportionately to the debris that fell in the lagoon. Additional information about the different tests can also be obtained from the 236 U/ 239 Pu and 240 Pu/ 239 Pu ratios, which are found to vary dramatically over the testing period. In particular, the first thermonuclear test, Ivy-Mike, has characteristic 236 U/ 239 Pu and 240 Pu/ 239 Pu signatures which are diagnostic of the first arrival of nuclear test material in various archives., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The rate of supernovae in our local Galactic neighbourhood within a distance of about 100 parsecs from Earth is estimated to be one every 2-4 million years, based on the total rate in the Milky Way (2.0 ± 0.7 per century). Recent massive-star and supernova activity in Earth's vicinity may be traced by radionuclides with half-lives of up to 100 million years, if trapped in interstellar dust grains that penetrate the Solar System. One such radionuclide is (60)Fe (with a half-life of 2.6 million years), which is ejected in supernova explosions and winds from massive stars. Here we report that the (60)Fe signal observed previously in deep-sea crusts is global, extended in time and of interstellar origin from multiple events. We analysed deep-sea archives from all major oceans for (60)Fe deposition via the accretion of interstellar dust particles. Our results reveal (60)Fe interstellar influxes onto Earth at 1.5-3.2 million years ago and at 6.5-8.7 million years ago. The signal measured implies that a few per cent of fresh (60)Fe was captured in dust and deposited on Earth. Our findings indicate multiple supernova and massive-star events during the last ten million years at distances of up to 100 parsecs.

The isotopes (236)U and (239)Pu, both produced during nuclear weapons tests carried out in the 1950s and 1960s, are present in the environment and may be used as tracers for soil erosion studies. Although these radionuclides occur only at ultra-trace levels in nature, they can be readily measured by accelerator mass spectrometry with the 14UD heavy ion accelerator at the Australian National University. We have analysed a series of vegetation samples for their (236)U and (239)Pu concentration and compared the results with those found in the surrounding soil. (236)U could be measured in all collected samples whereas (239)Pu could not be detected in several vegetation samples due to its very low concentration, although it was readily detectable in the soil. We find that, relative to plutonium, (236)U is preferentially taken up by plants with enrichment factors ((236)U/(239)Pu)veg/((236)U/(239)Pu)soil that range between 7 and 52 in the present study., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

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., (Crown Copyright © 2015. Published by Elsevier Ltd. All rights reserved.)

Here we present a nuclear forensic study of uranium from German nuclear projects which used different geometries of metallic uranium fuel. Through measurement of the (230)Th/(234)U ratio, we could determine that the material had been produced in the period from 1940 to 1943. To determine the geographical origin of the uranium, the rare-earth-element content and the (87)Sr/(86)Sr ratio were measured. The results provide evidence that the uranium was mined in the Czech Republic. Trace amounts of (236)U and (239)Pu were detected at the level of their natural abundance, which indicates that the uranium fuel was not exposed to any major neutron fluence., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In order to resolve a recent discrepancy in the half-life of 60Fe, we performed an independent measurement with a new method that determines the 60Fe content of a material relative to 55Fe (t1/2=2.744  yr) with accelerator mass spectrometry. Our result of (2.50±0.12)×10(6)  yr clearly favors the recently reported value (2.62±0.04)×10(6)  yr, and rules out the older result of (1.49±0.27)×10(6)  yr. The present weighted mean half-life value of (2.60±0.05)×10(6)  yr substantially improves the reliability as an important chronometer for astrophysical applications in the million-year time range. This includes its use as a sensitive probe for studying recent chemical evolution of our Galaxy, the formation of the early Solar System, nucleosynthesis processes in massive stars, and as an indicator of a recent nearby supernova.

The variation of the (236)U and (239)Pu concentrations as a function of depth has been studied in a soil profile at a site in the Southern Hemisphere well removed from nuclear weapon test sites. Total inventories of (236)U and (239)Pu as well as the (236)U/(239)Pu isotopic ratio were derived. For this investigation a soil core from an undisturbed forest area in the Herbert River catchment (17°30' - 19°S) which is located in north-eastern Queensland (Australia) was chosen. The chemical separation of U and Pu was carried out with a double column which has the advantage of the extraction of both elements from a relatively large soil sample (∼20 g) within a day. The samples were measured by Accelerator Mass Spectrometry using the 14UD pelletron accelerator at the Australian National University. The highest atom concentrations of both (236)U and (239)Pu were found at a depth of 2-3 cm. The (236)U/(239)Pu isotopic ratio in fallout at this site, as deduced from the ratio of the (236)U and (239)Pu inventories, is 0.085 ± 0.003 which is clearly lower than the Northern Hemisphere value of ∼0.2. The (236)U inventory of (8.4 ± 0.3) × 10(11) at/m(2) was more than an order of magnitude lower than values reported for the Northern Hemisphere. The (239)Pu activity concentrations are in excellent agreement with a previous study and the (239+240)Pu inventory was (13.85 ± 0.29) Bq/m(2). The weighted mean (240)Pu/(239)Pu isotopic ratio of 0.142 ± 0.005 is slightly lower than the value for global fallout, but our results are consistent with the average ratio of 0.173 ± 0.027 for the southern equatorial region (0-30°S)., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Measurements of total iodine (I) and iodine-129 ((129)I) concentrations in rivers and lakes of Argentina are presented. Their latitudinal distribution can be explained by taking into account their main sources (oceanic emissions and biomass burning for I, and atmospheric nuclear tests for (129)I), transport mechanisms, and fallout patterns. From the measured (129)I concentrations in the studied lakes, deposition fluences for their catchment areas were estimated. These results agree with a model of the global deposition pattern due to the (129)I released by atmospheric nuclear weapon tests and with other fluences reported for the southern hemisphere. In addition, the first measurements of (129)I in shallow seawater from the South Atlantic Ocean are presented and discussed.

In the present work, state of the art isotopic fingerprinting techniques are applied to an Arctic ice core in order to quantify deposition of U and Pu, and to identify possible tropospheric transport of debris from former Soviet Union test sites Semipalatinsk (Central Asia) and Novaya Zemlya (Arctic Ocean). An ice core chronology of (236)U, (239)Pu, and (240)Pu concentrations, and atom ratios, measured by accelerator mass spectrometry in a 28.6m deep ice core from the Austfonna glacier at Nordaustlandet, Svalbard is presented. The ice core chronology corresponds to the period 1949 to 1999. The main sources of Pu and (236)U contamination in the Arctic were the atmospheric nuclear detonations in the period 1945 to 1980, as global fallout, and tropospheric fallout from the former Soviet Union test sites Novaya Zemlya and Semipalatinsk. Activity concentrations of (239+240)Pu ranged from 0.008 to 0.254 mBq cm(-2) and (236)U from 0.0039 to 0.053 μBq cm(-2). Concentrations varied in concordance with (137)Cs concentrations in the same ice core. In contrast to previous published results, the concentrations of Pu and (236)U were found to be higher at depths corresponding to the pre-moratorium period (1949 to 1959) than to the post-moratorium period (1961 and 1962). The (240)Pu/(239)Pu ratio ranged from 0.15 to 0.19, and (236)U/(239)Pu ranged from 0.18 to 1.4. The Pu atom ratios ranged within the limits of global fallout in the most intensive period of nuclear atmospheric testing (1952 to 1962). To the best knowledge of the authors the present work is the first publication on biogeochemical cycles with respect to (236)U concentrations and (236)U/(239)Pu atom ratios in the Arctic and in ice cores., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A combination of state-of-the-art isotopic fingerprinting techniques and atmospheric transport modelling using real-time historical meteorological data has been used to demonstrate direct tropospheric transport of radioactive debris from specific nuclear detonations at the Semipalatinsk test site in Kazakhstan to Norway via large areas of Europe. A selection of archived air filters collected at ground level at 9 stations in Norway during the most intensive atmospheric nuclear weapon testing periods (1957-1958 and 1961-1962) has been screened for radioactive particles and analysed with respect to the concentrations and atom ratios of plutonium (Pu) and uranium (U) using accelerator mass spectrometry (AMS). Digital autoradiography screening demonstrated the presence of radioactive particles in the filters. Concentrations of (236)U (0.17-23nBqm(-3)) and (239+240)Pu (1.3-782μBqm(-3)) as well as the atom ratios (240)Pu/(239)Pu (0.0517-0.237) and (236)U/(239)Pu (0.0188-0.7) varied widely indicating several different sources. Filter samples from autumn and winter tended to have lower atom ratios than those sampled in spring and summer, and this likely reflects a tropospheric influence in months with little stratospheric fallout. Very high (236)U, (239+240)Pu and gross beta activity concentrations as well as low (240)Pu/(239)Pu (0.0517-0.077), (241)Pu/(239)Pu (0.00025-0.00062) and (236)U/(239)Pu (0.0188-0.046) atom ratios, characteristic of close-in and tropospheric fallout, were observed in filters collected at all stations in Nov 1962, 7-12days after three low-yield detonations at Semipalatinsk (Kazakhstan). Atmospheric transport modelling (NOAA HYSPLIT&#95;4) using real-time meteorological data confirmed that long range transport of radionuclides, and possibly radioactive particles, from Semipalatinsk to Norway during this period was plausible. The present work shows that direct tropospheric transport of fallout from atmospheric nuclear detonations periodically may have had much larger influence on radionuclide air concentrations and deposition than previously anticipated., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

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., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The construction of high resolution chronologies of sediment profiles corresponding to the last 50-100 years usually entails the measurement of fallout radionuclides (210)Pb and (137)Cs. The anthropogenic radionuclide, (137)Cs, originating from atmospheric nuclear weapons testing can provide an important "first appearance" horizon of known age (1954-1955), providing much-needed validation for the sometimes uncertain interpretations associated with (210)Pb geochronology. However, while (137)Cs usually provides a strong signal in sediment in the northern hemisphere, total fallout of (137)Cs in the southern hemisphere was only 25% that of the north and the low activities of (137)Cs seen in Australian and New Zealand sediments can make its horizon of first appearance somewhat arguable. Low (137)Cs fallout also limited the size of the 1963-1964 fallout peak, a peak that is usually seen in northern hemisphere sediment profiles but is often difficult to discern south of the equator. This paper shows examples of the use of nuclear weapons fallout Pu as a chronomarker in sediment cores from Australia (3 sites) and New Zealand (1 site). The Pu profiles of five cores are examined and compared with the corresponding (137)Cs profiles and (210)Pb geochronologies. We find that Pu has significant advantages over (137)Cs, including greater measurement sensitivity using alpha spectrometry and mass spectrometric techniques compared to (137)Cs measurements by gamma spectrometry. Moreover, Pu provides additional chronomarkers associated with changes in the Pu isotopic composition of fallout during the 1950s and 1960s. In particular, the (238)Pu/(239+240)Pu activity ratio shows distinct shifts in the early 1950s and the mid to late 1960s, providing important known-age horizons in southern hemisphere sediments. For estuarine and near-shore sediments Pu sometimes has another significant advantage over (137)Cs due to its enrichment in bottom sediment relative to (137)Cs resulting from the more efficient scavenging of dissolved Pu in seawater by sediment particles., (Copyright © 2009 Elsevier Ltd. All rights reserved.)

A study has been carried out to assess the potential of using fallout plutonium (Pu), which originated from atmospheric nuclear-weapons tests, as a tool to investigate recent erosional processes within the lower Cotter water-supply catchment in the Australian Capital Territory. This catchment, which was predominantly pine plantation, was severely affected by a major bush fire in 2003. Accelerator mass spectrometry has been used to measure Pu in soil samples collected from a number of sites across the catchment. The results indicate that less than 1cm of surface soil had been lost since the early 1960s over much of the catchment. Areas of more erodible soil have, however, lost 2-4cm of topsoil, and a loss of ∼6cm of soil was identified at one particular site., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

A first international (36)Cl interlaboratory comparison has been initiated. Evaluation of the final results of the eight participating accelerator mass spectrometry (AMS) laboratories on three synthetic AgCl samples with (36)Cl/Cl ratios at the 10(-11), 10(-12), and 10(-13) level shows no difference in the sense of simple statistical significance. However, more detailed statistical analyses demonstrate certain interlaboratory bias and underestimation of uncertainties by some laboratories. Following subsequent remeasurement and reanalysis of the data from some AMS facilities, the round-robin data indicate that (36)Cl/Cl data from two individual AMS laboratories can differ by up to 17%. Thus, the demand for further work on harmonising the (36)Cl-system on a worldwide scale and enlarging the improvement of measurements is obvious.

To study the Pu concentration and isotope ratio distributions present in China, the (239+240)Pu total activities and (240)Pu/(239)Pu atom ratios in core soil samples from Hubei Province in central China were investigated using Accelerator Mass Spectrometry (AMS). The activities ranged from 0.019 to 0.502 mBqg(-1) and the (239+240)Pu inventories of 45 and approximately 55 Bqm(-2) agree well with that expected from global fallout. The (240)Pu/(239)Pu atom ratios in the soil ranged from 0.172 to 0.220. The ratios are similar to typical global fallout values. Hence, any close-in fallout contribution from the Chinese nuclear weapons tests, mainly conducted in the 1970s, must have either been negligible or had a similar (240)Pu/(239)Pu ratio to that of global fallout. The top 10 cm layer of the soil contributes approximately 90% of the total inventory and the maximum concentrations appeared in the 2-4 cm or 4-6 cm layers. It is suggested that climatic conditions and organic content are the two main factors that affect the vertical migration of plutonium in soil.

Following atmospheric nuclear weapons testing in the 1950s and 1960s significant quantities of (137)Cs and (239+240)Pu were deposited worldwide. In recent decades, (137)Cs has been commonly used as a tracer of soil erosion and sedimentation, particularly in the Northern Hemisphere where atomic deposition was three times as great as in the Southern Hemisphere. The relatively short 30-year half-life of this isotope means that its sensitivity as a tracer is rapidly decreasing. In contrast, with half-lives of 24,110 and 6561 years, the sensitivity of the two plutonium isotopes remains essentially the same as when it was deposited. Here we use the technique of Accelerator Mass Spectrometry to demonstrate the potential of anthropogenic Pu as an alternative to (137)Cs as a tracer of soil transport in Australia. We measure an average (137)Cs/(239+240)Pu activity ratio of 27.3+/-1.5 and an average (240)Pu/(239)Pu atom ratio of 0.149+/-0.003, both slightly lower than the global average.

The National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) for seaweed was developed through an interlaboratory comparison with 24 participants from 16 countries. After evaluating different techniques to calculate certified values for the radionuclides, the median method was found to be the most representative technique. The certified values were provided for 13 radionuclides and information values were given for 15 more radionuclides. Results for the natural decay series showed disequilibrium in both the uranium and thorium series.