Record of 3H and 36Cl from the Fukushima nuclear accident recovered from soil water in the unsaturated zone at Koriyama.

The opportunity to measure the concentrations of 3H and 36Cl 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 3H and 36Cl 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 3H and 36Cl from the accident are 1.4 × 1013 and 2.0 × 1012 atoms m-2 respectively at this site. Very high concentrations of both 3H (46 Bq L-1) and 36Cl (3.36 × 1011 atoms L-1) were found in the unsaturated soil at depths between 300 and 350 cm. From these, conservative estimates for the 3H and 36Cl concentrations in the precipitation in the ~ 6 weeks following the accident were 607 Bq L-1 and 4.74 × 1010 atoms L-1, respectively. A second hole drilled in 2016 showed that 3H concentrations in the unsaturated soil and shallow groundwater had returned to close to natural levels, although the 36Cl concentrations were still significantly elevated above natural levels.

Plutonium isotopes in the North Western Pacific sediments coupled with radiocarbon in corals recording precise timing of the Anthropocene.

Plutonium (Pu) has been used as a mid-twentieth century time-marker in various geological archives as a result of atmospheric nuclear tests mainly conducted in 1950s. Advancement of analytical techniques allows us to measure 239Pu and 240Pu more accurately and can thereby reconstruct the Pacific Pu signal that originated from the former Pacific Proving Grounds (PPG) in the Marshall Islands. Here, we propose a novel method that couples annual banded reef building corals and nearshore anoxic marine sediments to provide a marker to precisely determine the start of the nuclear era which is known as a part of the Anthropocene. We demonstrate the efficacy of the methods using sediment obtained from Beppu Bay, Japan, and a coral from Ishigaki Island, Japan. The sedimentary records show a clear Pu increase from 1950, peaking during the 1960s, and then showing a sharp decline during the 1970s. However, a constantly higher isotope ratio between 239Pu and 240Pu suggest an additional contribution other than global fallout via ocean currents. Furthermore, single elevations in 240Pu/239Pu provide supportive evidence of close-in-fallout similar to previous studies. Coral skeletal radiocarbon displays a clear timing with the signatures supporting the reliability of the Beppu Bay sediments as archives and demonstrates the strength of this method to capture potential Anthropocene signatures.

The 240Pu/239Pu atom ratio in Chinese soils.

The 240Pu/239Pu 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 240Pu/239Pu 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 240Pu/239Pu atom ratios in Chinese soils is investigated. An area to the West of Xining City, shows a weighted average 240Pu/239Pu atom ratio of 0.167 ±â€¯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 240Pu/239Pu ratio of 0.182 ±â€¯0.002 suggests that global fallout is the main source of Pu in most Chinese soils.

Limits on Supernova-Associated

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).

Continuous transport of Pacific-derived anthropogenic radionuclides towards the Indian Ocean.

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.

Uranium from German Nuclear Power Projects of the 1940s--A Nuclear Forensic Investigation.

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.

(129)I dispersion in Argentina: concentrations in fresh and marine water and deposition fluences in Patagonia.

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.

Long-range tropospheric transport of uranium and plutonium weapons fallout from Semipalatinsk nuclear test site to Norway.

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_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.

Concentration and characterization of plutonium in soils of Hubei in central China.

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.

Use of airborne gamma-ray spectrometry for environmental assessment of the rehabilitated nabarlek uranium mine, Australia.

This article describes an airborne gamma survey of a 7 x 5 km region around the rehabilitated Nabarlek uranium mine in northern Australia. An unusually tight line spacing (100 m) and low aircraft height (50 m) were used, enabling the survey to distinguish man-made structures such as ponds and accommodation areas, as well as creek lines. Positive correlations between airborne data and ground-based readings enabled an estimation of the average absorbed dose rate arising from terrestrial gamma radiation over large areas of the site to be derived. For the fenced minesite area this estimate was 0.31 micro Gy hr(- 1). The airborne survey data were found to be invaluable in helping to plan further ground-level investigations and showed promise as an assessment tool for rehabilitated minesites.

Geographic variability in radon exhalation at a rehabilitated uranium mine in the Northern Territory, Australia.

In this study, dry season radon flux densities and radon fluxes have been determined at the rehabilitated Nabarlek uranium mine in northern Australia using conventional charcoal canisters. Environmental background levels amounted to 31+/- 15 milli Becquerel per m(2) per second (mBq m(-2) s(-1)). Radon flux densities within the fenced rehabilitated mine area showed large variations with a maximum of 6500 mBq m(-2) s(-1) at an area south of the former pit characterised by a disequilibrium between (226)Ra and (238)U. Radon flux densities were also high above the areas of the former pit (mean 971 mBq m(-2) s(-1)) and waste rock dump (mean 335 mBq m(-2) s(-1)). The lower limit for the total pre-mining radon flux from the fenced area (140 ha) was estimated to 214 kBq s(-1), post-mining radon flux amounted to 174 kBq s(-1). Our study highlights that the results of radon flux studies are vitally dependant on the selection of individual survey points. We suggest the use of a randomised system for both the selection of survey points and the placement of charcoal canisters at each survey point, to avoid over estimation of radon flux densities. It is also important to emphasize the significance of having reliable pre-mining radiological data available to assess the success of rehabilitation of a uranium mine site.