882 research outputs found

    Transport of Sellafield-derived C-14 from the Irish Sea through the North Channel

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    Since the early 1950s, the Sellafield nuclear fuel reprocessing plant in Northwest England has released radio-carbon into the Irish Sea in a mainly inorganic form as part of its authorized liquid effluent discharge. In contrast to the trend in which the activities of most radionuclides in the Sellafield liquid effluent have decreased substantially, C-14 discharges have increased since 1994-95. This has largely been due to a policy change favoring marine discharges over atmospheric discharges. C-14 is radiologically important due to its long half life, mobility in the environment, and propensity for entering the food chain. Current models for radionuclide dispersal in the Irish Sea are based on a reversible equilibrium distribution coefficient (k(d)), an approach which has been shown to be inadequate for C-14. Development of predictive models for the fate of Sellafield-derived C-14 requires a thorough understanding of the biogeochemical fluxes between different carbon reservoirs and the processes controlling the net flux of C-14 out of the Irish Sea, through he North Channel. In this study., both an empirical and a halving time approach indicate that close to 100% of the C-14 that is discharged from Sellafield is dispersed beyond the Irish Sea on a time-scale of months in the form of DIC, with little transfer to the PIC, POC, and DOC fractions, indicating that the "dilute and disperse" mechanism is operating satisfactorily. This is consistent with previous research that indicated little transfer of C-14 to Irish Sea sediments, While significant C-14 enhancements have been observed in the biota of the Irish Sea, this observation is not necessarily in conflict with either of the above as the total biomass has to be taken into account in any calculations of C-14 retention within the Irish Sea

    Sources of anthropogenic C-14 to the North Sea

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    The Sellafield nuclear fuel reprocessing plant on the northwest coast of England is the largest source of anthropogenic radiocarbon to the UK coastal environment. In a mid-1990s study of C-14 distribution around the UK coast, the pattern of dilution with increasing distance from Sellafield appeared to be perturbed by anomalously high C-14 activities in marine biota in the coastal environment of northeast England. This present study was undertaken during 1998 and 1999 to determine whether this C-14 enhancement was due to Sellafield or the nuclear power plants on the east coast. Seawater, seaweed (Fucus sp.), and mussel (Mytilus edulis) samples that were collected from the vicinity of the Torness and Hartlepool advanced gas-cooled reactor (AGR) nuclear power stations were all enhanced above the contemporary regional background activity derived from natural production and atmospheric nuclear weapons testing. We used previously published dilution factors and transfer times for Tc-99 between Sellafield and various points on the UK coast to determine likely Sellafield- derived C-14 contributions to the activities at the nuclear power plant sites. The results suggest that the activities observed at Torness, which are only marginally enhanced above the natural background activity, are possibly due to discharges from Sellafield; however, the significant C-14 enhancements at Hartlepool are not Sellafield-derived. Furthermore, since both reactors have the same fundamental design, the low activities at the Torness AGR imply that the activities at Hartlepool are not from the AGR, suggesting that there is an input of C-14 to the marine environment in the vicinity of Hartlepool which is probably non-nuclear-power related. However, there is no other authorized site in the area that could account for the observed C-14 enrichments; therefore, further research is required to ascertain the source of this C-14

    A study of the elements copper through uranium in Sirius A: Contributions from STIS and ground-based spectra

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    We determine abundances or upper limits for all of the 55 stable elements from copper to uranium for the A1 Vm star Sirius. The purpose of the study is to assemble the most complete picture of elemental abundances with the hope of revealing the chemical history of the brightest star in the sky, apart from the Sun. We also explore the relationship of this hot metallic-line (Am) star to its cooler congeners, as well as the hotter, weakly- or non-magnetic mercury-manganese (HgMn) stars. Our primary observational material consists of {\em Hubble Space Telescope} (HSTHST) spectra taken with the Space Telescope Imaging Spectrograph (STIS) in the ASTRAL project. We have also used archival material from the %\citep/{ayr10}. COPERNICUSCOPERNICUS satellite, and from the HSTHST Goddard High-Resolution Spectrograph (GHRS), as well as ground-based spectra from Furenlid, Westin, Kurucz, Wahlgren, and their coworkers, ESO spectra from the UVESPOP project, and NARVAL spectra retrieved from PolarBase. Our analysis has been primarily by spectral synthesis, and in this work we have had the great advantage of extensive atomic data unavailable to earlier workers. We find most abundances as well as upper limits range from 10 to 100 times above solar values. We see no indication of the huge abundance excesses of 1000 or more that occur among many chemically peculiar (CP) stars of the upper main sequence. The picture of Sirius as a hot Am star is reinforced.Comment: With 6 Figures and 4 Tables; accepted for publication in Ap

    Effects of 1,25 Dihydroxyvitamin D3 and Calcium on Growth and Differentiation and on c-fos and p53 Gene Expression in Normal Human Keratinocytes

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    Calcium enhances keratinocyte differentiation, and 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) is both antiproliferative and prodifferentiative in many cell types, including normal human keratinocytes. In the present study, we examined the combined effects of calcium and 1,25(OH)2D3 on parameters of growth and differentiation and on c-fos and p53 gene expression in normal human keratinocytes. Exposure of normal human keratinocytes to 1,25(OH)2D3 markedly reduced [3H] thymidine incorporation and cell number at low and high medium Ca++ concentrations. Simultaneously, cells in the G0/G1 phase of the cell cycle increased significantly and those in the S phase fell precipitously. l,25(OH)2D3 and calcium also induced keratinocyte differentiation independently, as assessed by iminuno- cytochemistry and by induction of involucrin mRNA. Both Ca++ and 1,25(OH)2D3 were shown, by nuclear run-on assays, to increase involucrin gene transcription. A rapid, transient elevation in c-fos protooncogene expression preceded these effects when epidermal growth factor was present alone. When 1,25(OH)2D3 was added to quiescent keratinocytes, there was a marked augmentation of c-fos mRNA accumulation at low and high medium Ca++ concentrations. Varying medium Ca++ concentrations had no effect on c-fos mRNA levels. Increasing medium Ca++ concentrations from 0.15 to 2.0mM produced marked elevations of p53 mRNA accumulation and of the rate of p53 gene transcription, whereas 1,25(OH)2D3 had no effect.These results, therefore, suggest that 1,25(OH)2D3 and calcium act in concert to modulate the expression of two important cell-cycle-associated genes, which may be important components in the initial programming of growth and differentiation of normal human keratinocytes
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