The early solar system abundance of /sup 244/Pu as inferred from the St. Severin chondrite

We describe the analysis of Xe released in stepwise heating of neutron-irradiated samples of the St. Severin chondrite. This analysis indicates that at the time of formation of most chondritic meteorites, approximately 4.56 x 10/sup 9/ years ago, the atomic ratio of /sup 244/Pu//sup 238/U was 0.0068 +- 0.0010 in chondritic meteorites. We believe that this value is more reliable than that inferred from earlier analyses of St. Severin. We feel that this value is currently the best available estimate for the early solar system abundance of /sup 244/Pu. 42 refs., 2 tabs

Incorporation of hydrothermal elements in foraminiferal calcite: Results from culturing experiments

The trace race element chemistry of foraminiferal tests reflect the environment in which they grew. Thus geochemical data can be used as paleo-proxies constraining environmental conditions in ancient seas [e.g.: 1]. Seawater chemistry may be influenced by local sources such as hydrothermal activity. However, for elements considered diagnostic for hydrothermalism, reliable experimental data is rare [e.g. 2]. To provide a solid basis for a more complete understanding of trace element partitioning between foraminiferal calcite and seawater, we carried out culture experiments under controlled laboratory conditions. This is the main objective of our study.For our experiment we grew freshly collected benthic foraminifera (Ammonia tepida) in seawater, containing a cocktail of Mn, Co, Ni and Cu, at defined trace element levels.Measurements of the culture solutions were carried out regularly by HR-ICP-MS whereas the calcite of newly grown chambers of the cultured foraminifera was detected by a non-destructive technique - µSy-XRF [3]. To confirm the data LA-ICP-MS measurements have been performed. To distinguish between old and new chambers the calcein labeling technique [4] was applied.First results demonstrate that especially Ni and Cu could be determined with high precission and accuracy using µSy-XRF measurements. We determined trace element/Ca ratios and DNi as well as DCu using LA ICP-MS

What CO2 well gases tell us about the origin of noble gases in the mantle and their relationship to the atmosphere

Study of commercially produced volcanic CO2 gas associated with the Colorado Plateau, USA, has revealed substantial new information about the noble gas isotopic composition and elemental abundance pattern of the mantle. Combined with published data from mid-ocean ridge basalts, it is now clear that the convecting mantle has a maximum 20Ne/22Ne isotopic composition, indistinguishable from that attributed to solar wind-implanted (SWI) neon in meteorites. This is distinct from the higher 20Ne/22Ne isotopic value expected for solar nebula gases. The non-radiogenic xenon isotopic composition of the well gases shows that 20 per cent of the mantle Xe is ‘solar-like’ in origin, but cannot resolve the small isotopic difference between the trapped meteorite ‘Q’-component and solar Xe. The mantle primordial 20Ne/132Xe is approximately 1400 and is comparable with the upper end of that observed in meteorites. Previous work using the terrestrial 129I–129Xe mass balance demands that almost 99 per cent of the Xe (and therefore other noble gases) has been lost from the accreting solids and that Pu–I closure age models have shown this to have occurred in the first ca 100 Ma of the Earth's history. The highest concentrations of Q-Xe and solar wind-implanted (SWI)-Ne measured in meteorites allow for this loss and these high-abundance samples have a Ne/Xe ratio range compatible with the ‘recycled-air-corrected’ terrestrial mantle. These observations do not support models in which the terrestrial mantle acquired its volatiles from the primary capture of solar nebula gases and, in turn, strongly suggest that the primary terrestrial atmosphere, before isotopic fractionation, is most probably derived from degassed trapped volatiles in accreting material. By contrast, the non-radiogenic argon, krypton and 80 per cent of the xenon in the convecting mantle have the same isotopic composition and elemental abundance pattern as that found in seawater with a small sedimentary Kr and Xe admix. These mantle heavy noble gases are dominated by recycling of air dissolved in seawater back into the mantle. Numerical simulations suggest that plumes sampling the core–mantle boundary would be enriched in seawater-derived noble gases compared with the convecting mantle, and therefore have substantially lower 40Ar/36Ar. This is compatible with observation. The subduction process is not a complete barrier to volatile return to the mantle

Failure to clear persistent vaccine-derived neurovirulent poliovirus infection in an immunodeficient man

Background Individuals who chronically excrete neurovirulent poliovirus of vaccine-origin are of considerable concern to the Global Polio Eradication programme. Chronic infection with such polioviruses is a recognised complication of hypogammaglobulinaernia.Methods We did a series of in-vitro and in-vivo therapeutic studies, with a view to clearing persistent neurovirulent poliovirus infection in an individual with common variable immunodeficiency, using oral immunoglobulin, breast milk (as a source of secretory IgA), ribavirin, and the anti-picornaviral agent pleconaril. We undertook viral quantitation, antibody neutralisation and drug susceptibility assays, and viral gene sequencing.Findings Long-term asymptomatic excretion of vaccine-derived neurovirulent poliovirus 2 was identified in this hypogammaglobulinaemic man, and was estimated to have persisted for up to 22 years. Despite demonstrable in-vitro neutralising activity of immunoglobulin and breast milk, and in-vitro antiviral activity of ribavirin, no treatment was successful at clearing the virus, although in one trial breast milk significantly reduced excretion levels temporarily. During the course of study, the virus developed reduced susceptibility to pleconaril, precluding the in-vivo use of this drug. Sequence analysis revealed the emergence of a methionine to leucine mutation adjacent to the likely binding site of pleconaril in these isolates.Interpretation Chronic vaccine-associated poliovirus infection in hypogammaglobulinaemia is a difficult condition to treat. It represents a risk to the strategy to discontinue polio vaccination once global eradication has been achieved