4051 research outputs found
Sort by
Single pixel compressive gamma-ray imaging with randomly encoded masks
No full textWe report on the development and demonstration of a single pixel spectroscopic gamma-ray imaging concept based on the principles of compressed sensing. Compressive gamma-ray images were obtained for both point sources and complex extended sources. The reconstruction of images at different photon energies allowed the spatial mapping of different radionuclides. When compared to traditional aperture based gamma-ray imaging techniques, the point source images were generated with ten times fewer measurements. More complex extended source images were generated with up to three times fewer measurements. Gamma-ray imaging techniques designed around the principles of compressed sensing have the potential to exploit the sparsity typically found in gamma-ray images, leading to a new class of fast and low cost imaging systems. © Copyright 2020 IOP Publishin
Plutonium uptake in biota at former nuclear sites
No full textPlutonium (Pu) is of ongoing interest as worldwide inventories continue to increase and plans for permanent storage of Pu wastes have stalled in many countries leaving large amounts in temporary storage. Pu also remains as environmental contamination at various locations due to: accidents (e.g., Chernobyl, UKR; Thule, GRL); research and processing releases (e.g., Los Alamos, USA, Mayak, RUS); and former weapons testing (e.g., Nevada Test Site, USA; Semipalatinsk, KAZ; and Maralinga, AUS). We assessed the availability and uptake of Pu in a range of wildlife types at legacy sites with the focus on new data from outside of the remediation zone at the former Taranaki site, Maralinga, South Australia. Of key interest are the uptake and biokinetics of Pu in mammals, particularly from environmental exposure to the undetonated Pu-oxide forms at Taranaki that are representative of much of the worldwide inventory. Our results confirm that environmentally dispersed Pu can remain accessible for uptake by biota over decadal time scales. For example, after more than 50 years since deposition at Taranaki, 62% of Pu has remained in the 0-2 cm surface layer, and nearly 100% in the 0-10 cm of soil depths. Although a small fraction of the Pu is migrating downward at —0.2 cm per year, it appears that most Pu will continue to remain accessible into the future for plants and animals that inhabit the surface, or shallow soil layers. The uptake of Pu into terrestrial animals occurs mainly by inhalation and ingestion, and can be persistent over time as indicated by constant uptake rates for mammals, and a potential increase for reptiles, in data spanning 30 years. The rates of soil-to-animal transfer at Taranaki, align well with those from similar sites where undetonated Pu was tested (e.g., Nevada Test Site, US). However, the uptake values at these sites are lower than general world-wide values, likely due to the presence of less-absorbable forms of Pu. The importance of the physico-chemical form of the Pu on uptake was also seen in data from fish exposed to more absorbable forms of Pu in liquid discharge ponds near processing facilities in the US. These fish had two orders of magnitude higher uptake values than those for similar species receiving Pu solely from atmospheric fallout. The physico-chemical form of the Pu can also influence how it is distributed among mammalian organs. The relatively insoluble forms at Taranaki, which include particulates, led to elevated concentrations of unabsorbed Pu in the lung, gastrointestinal tract, and adhered to skin/fur of mammals. This elevated Pu can provide a secondary source during human, and ecological, food-chain consumption. Of the Pu that was absorbed within the body, much higher accumulation was measured in the skeleton, and much lower in the liver, in mammals at Taranaki as compared with the standard model of 50% skeleton, and 30% liver (ICRP 1986). Our data provides specific quantification of Pu uptake rates in wildlife and the subsequent accumulation in various mammalian organs. These will aid future assessments of the Maralinga site, as well as more general evaluations related to the low-solubility forms of Pu that make up a large share of the worldwide inventory
Artificial radiotracer applications in aquatic environment
No full textThe use of artificial radiotracers in the environment is analogous to their use in the human body. In both domains they provide data on flow rates and pathways, on exchange with materials and on their final discharge from the studied system. Artificially injected radiotracers have been used to investigate flow in natural waters since the 1950's. Identification of flow paths, diagnosis of blockages or leakage, measurement of flow rates, dispersion and exchange processes, such as biological uptake or sorption, are all aspects to which a wide range of artificial radioactive tracers have been applied. Increasingly radiotracers are used in combination with numerical modelling to improve confidence in the predictive capacity of models used in the management of our water resources and to extend their spatial applicability. In turn this allows us to use less and less tracer and demonstrate that the human and environmental impact of modern radiotracer studies is minimal. © The authors.https://inis.iaea.org/collection/NCLCollectionStore/_Public/46/062/46062646.pdfInternational Atomic Energy Agenc
A landscape-scale approach to examining the fate of atmospherically derived industrial metals in the surficial environment
No full textIndustrial metals are now ubiquitous within the atmosphere and their deposition represents a potential source of contamination to surficial environments. Few studies, however, have examined the environmental fate of atmospheric industrial metals within different surface environments. In this study, patterns of accumulation of atmospherically transported industrial metals were investigated within the surface environments of the Snowy Mountains, Australia. Metals, including Pb, Sb, Cr and Mo, were enriched in aerosols collected in the Snowy Mountains by 3.5–50 times pre-industrial concentrations. In sedimentary environments (soils, lakes and reservoirs) metals showed varying degrees of enrichment. Differences were attributed to the relative degree of atmospheric input, metal sensitivity to enrichment, catchment area and metal behaviour following deposition. In settings where atmospheric deposition dominated (ombrotrophic peat mires in the upper parts of catchments), metal enrichment patterns most closely resembled those in collected aerosols. However, even in these environments significant dilution (by 5–7 times) occurred. The most sensitive industrial metals (those with the lowest natural concentration; Cd, Ag, Sb and Mo) were enriched throughout the studied environments. However, in alpine tarn-lakes no other metals were enriched, due to the dilution of pollutant-metals by catchment derived sediment. In reservoirs, which were located lower within catchments, industrial metals exhibited more complex patterns. Particle reactive metals (e.g. Pb) displayed little enrichment, implying that they were retained up catchment, whereas more soluble metals (e.g., Cu and Zn) showed evidence of concentration. These same metals (Cu and Zn) were depleted in soils, implying that they are preferentially transported through catchments. Enrichment of other metals (e.g. Cd) varied between reservoirs as a function of contributing catchment area. Overall this study showed that the fate of atmospherically derived metals is complex, and depends upon metal behaviour and geomorphic processes operating at landscape scales. © 2014 Elsevier B.V
Regional controls on holocene sedminentation patterns along the Peru contonental margin; long term implications for El Niño-Southern Oscillation
Get PDFNot availabl
A radon-only technique for quantifying the effects of atmospheric stability on air pollution concentrations
No full textRadon-222 is a useful tool for quantifying stability influences on urban pollutant concentrations. While bulk radon gradients are ideal for this purpose, since the vertical differencing substantially removes contributions from processes on timescales greater than diurnal, more commonly radon measurements are available only at a single height. Here we explain why single-height, near-surface (<20 m agl) radon observations should not be used quantitatively as an indicator of atmospheric stability without prior conditioning of the time series to remove contributions from larger-scale “non-local” (including fetch-related) processes. We outline a simple technique to obtain an approximation of the diurnal radon gradient signal from a single-height measurement time series, and use it to derive a 4-category classification scheme for atmospheric stability on a “whole night” basis. We then apply this stability classification scheme to selected climatological and pollution observations, and compare the results with stability classifications performed using the Pasquil-Gifford “turbulence” and “radiation” schemes. Lastly, we apply the radon-based classification scheme to nocturnal mixing height estimates calculated from the diurnal radon accumulation time series, and provide insight to the range of nocturnal mixing depths expected for each of the stability classes
Late Holocene record of environmental changes, cyclones and tsunamis in a coastal lake, Mangaia, Cook Islands
No full textA 4.3 m‐long peat sequence from the shore of Lake Tiriara, Mangaia, Cook Islands, was analyzed using an ITRAX core scanner equipped with a magnetic susceptibility meter. Variations in the elemental profiles, providing insights into long‐ and short‐term environmental changes over the last 3500 years, are supported by grain size data and diatom assemblages. The scattering ratio (Mo Inc/Mo Coh) was evaluated and found to represent a good proxy for organic matter in peat. X‐Ray Fluorescence (XRF) data were processed by principal component analysis that confirmed the distinction of biogenic and detrital phases, organic matter and elements of marine origin. The record preserved in the peat sequence includes a peatland infilling stage followed by alternating drier and wetter periods. A notable steady increase in clay associated with high counts of detrital elements from 2000–1700 cal yr BP is attributed to increased erosion, which is most probably linked with human colonization and/or more intense chemical weathering linked with a wetter climate. Freshwater gastropods (Melanoides sp. ), which were possibly introduced by humans, or are native, occupied the wetland during a period of lower water level about 1000–1100 cal yr BP. Short‐term changes in the elemental profiles are often linked with slight coarsening of the inorganic fraction that is, however, only revealed after grain size analysis. Peaks in marine indicators (Br, Cl, S, and/or Ca) associated with marine‐dominated diatom assemblages most probably represent marine incursions through the underground tunnel in the makatea, a fossilized, uplifted coral limestone rim. While none of the marine event units present characteristics typical of cyclone or tsunami deposits, the concurrent or absent peak of detrital elements (Fe, Si, Rb, Ti, K) attributed to increased erosion of the volcanic cone associated with a cyclone is used to distinguish both types of events, as also suggested by principal component analysis. © 1999-2020 John Wiley & Sons, Inc
Can IBA techniques quantify the contributions of deserts, winter domestic heating and coal fired power stations to the ambient fine particle air pollution concentrations in the Sydney Basin?
Get PDFANSTO has used accelerator based ion beam analysis (IBA) techniques to characterise, fingerprint and source fine particles in and around Australia since the early 1990's. This large database covering many years allows us to now look quantitatively at fine particle sources, including automobiles, smoke, sea spray, soils and industrial emissions. This talk will discuss the accelerator based IBA techniques and how they are used to identify the contributions of windblown soils, wood heating and coal fired power stations to ambient air pollution in the Sydney Basin between 1998 and the present
The future of radiotracing
No full textRadiotracing has enormous potential to provide data to underpin environmental management in aquatic ecosystems. The use of tracer data to validate numerical models, improvements in data acquisition and new tracer forms provide the basis for the future of radiotracing. However, an increasing regulatory burden, reduction in tracer availability and a loss of technical expertise threaten this field of study. Standardisation of tracer approaches where possible and new work on assessing the impact of radiotracers on non-human biota are two areas that may enable the future use of radiotracers at a field scale in engineering and research applications. © The authors.International Atomic Energy Agenc
Ice core measurements of 14CH4 show no evidence of methane release to atmosphere from methane hydrates during a large warming event 11,600 years ago
No full textThawing permafrost and marine methane hydrate destabilization have been proposed as large sources of methane to the atmosphere in response to both past and future warming.
We present measurements of 14C of paleoatmospheric CH4 over the Younger Dryas – Preboreal (YD – PB) abrupt warming event (≈11,600 years ago) from ancient ice
outcropping at Taylor Glacier, Antarctica. The YD – PB event was associated with a ≈ 50% increase in atmospheric CH4 concentrations. 14C can unambiguously identify CH4 emissions from “old carbon” sources, such as permafrost and CH4 hydrates. The only prior study of
paleoatmospheric 14CH4 (from Greenland ice) suggested that wetlands were the main
driver of the YD - PB CH4
increase, but the results were weakened by an unexpected and poorly understood 14CH4 component from in situ cosmogenic production directly in nearsurface
ice. In this new study, we have been able to accurately characterize and correct for
the cosmogenic 14CH4
component. All samples from before, during and after the abrupt warming and associated CH4 increase yielded 14CH4 values that are consistent with 14C of
atmospheric CO2 at that time, indicating a purely contemporaneous methane source. These new measurements rule out the possibility of large CH4
releases to the atmosphere from
methane hydrates or old permafrost carbon in response to the large and rapid YD - PB
warming, and confirm that wetlands were the main driver of the CH4 increase