βdecay of the 21/2^+ isomer in ^<93>Mo and level structure of ^<93>Nb

The γ rays associated with β decay of the 21/2^+ isomer in ^Mo (Ex=2.425 MeV, T_=6.85 h) were measured with a selective sensitivity to long-lived isomer decays. A new 1262-keV transition was found in the γ-γ coincidence measurement, and it was attributed to a transition in ^Nb, which is the daughter nucleus of the β decay of the ^Mo isomer, from the 2.753- to the 1.491-MeV levels. Accurate γ-ray intensity balances have determined the β-decay intensity from the ^Mo isomer to the 2.753-MeV level in ^Nb and placed no appreciable intensity for the previously reported β-decay branching to the 2.180-MeV level, for which a recent in-beam γ-ray experiment assigned to be I^π = 17/2^-. Based on the γ-ray intensities from the 2.753-MeV level, spin-parity assignment of this level was revised from 21/2^+ to 19/2^+. The observed β-decay intensity and the spin-parity assignment were explained by the jj-coupling shell model calculations

Synthesis of hypericin via emodin anthrone derived from a two-fold diels-alder reaction of 1,4-benzoquinone

This is a preprint of an article published in Natural Product Communications. 2(1):67-70 (2007).http://www.naturalproduct.us/ArticleNatural Product Communications. 2(1):67-70 (2007)journal articl

Arsenic chemistry in soils and sediments

Arsenic is a naturally occurring trace element that poses a threat to human and ecosystem health, particularly when incorporated into food or water supplies. The greatest risk imposed by arsenic to human health results from contamination of drinking water, for which the World Health Organization recommends a maximum limit of 10 {micro}g L{sup -1}. Continued ingestion of drinking water having hazardous levels of arsenic can lead to arsenicosis and cancers of the bladder, skin, lungs and kidneys. Unfortunately, arsenic tainted drinking waters are a global threat and presently having a devastating impact on human health within Asia. Nearly 100 million people, for example, are presently consuming drinking water having arsenic concentrations exceeding the World Health Organization's recommended limit (Ahmed et al., 2006). Arsenic contamination of the environment often results from human activities such as mining or pesticide application, but recently natural sources of arsenic have demonstrated a devastating impact on water quality. Arsenic becomes problematic from a health perspective principally when it partitions into the aqueous rather than the solid phase. Dissolved concentrations, and the resulting mobility, of arsenic within soils and sediments are the combined result of biogeochemical processes linked to hydrologic factors. Processes favoring the partitioning of As into the aqueous phase, potentially leading to hazardous concentrations, vary extensively but can broadly be grouped into four categories: (1) ion displacement, (2) desorption (or limited sorption) at pH values &gt; 8.5, (3) reduction of arsenate to arsenite, and (4) mineral dissolution, particularly reductive dissolution of Fe and Mn (hydr)oxides. Although various processes may liberate arsenic from solids, a transition from aerobic to anaerobic conditions, and commensurate arsenic and iron/manganese reduction, appears to be a dominant, but not exclusive, means by which high concentrations of dissolved arsenic are generated. Within the subsequent sections of this chapter, we explore and describe the biological and chemical processes that control the partitioning of arsenic between the solid and aqueous phase

Revised spin-parity assignment and a new interpretation of the high-spin isomer in

The high-spin isomer in 151Er ( E x = 10.3 MeV, T 1/2 = 420 ns) has been studied by the 116Sn ( 40Ar , 5n) 151Er reaction at 197MeV. From the $\gamma \gamma$ coincidence relations, a new transition with an energy of 1514keV was found. This finding requires the revision of the spin-parity assignment from previous 67/2- to 61/2+ or 65/2- . The 61/2+ assignment is the one which was predicted by the deformed independent particle model as an isomer with a large oblate deformation ( $\beta$ = - 0.17) of the \ensuremath[\nu(f_{7/2}h_{9/2} i_{13/2}) \pi(h^4_{11/2})]_{61/2^+} configuration. The isomerism may be attributed to the sudden shape change of the isomer from the nearly spherical shape of the lower-spin yrast states to the oblate shape

Arsenic Release Metabolically Limited to Permanently Water-Saturated Soil in Mekong Delta

Microbial reduction of arsenic-bearing iron oxides in the deltas of South and Southeast Asia produces widespread arsenic-contaminated groundwater. Organic carbon is abundant both at the surface and within aquifers, but the source of organic carbon used by microbes in the reduction and release of arsenic has been debated, as has the wetland type and sedimentary depth where release occurs. Here we present data from fresh-sediment incubations, in situ model sediment incubations and a controlled field experiment with manipulated wetland hydrology and organic carbon inputs. We find that in the minimally disturbed Mekong Delta, arsenic release is limited to near-surface sediments of permanently saturated wetlands where both organic carbon and arsenic-bearing solids are sufficiently reactive for microbial oxidation of organic carbon and reduction of arsenic-bearing iron oxides. In contrast, within the deeper aquifer or seasonally saturated sediments, reductive dissolution of iron oxides is observed only when either more reactive exogenous forms of iron oxides or organic carbon are added, revealing a potential thermodynamic restriction to microbial metabolism. We conclude that microbial arsenic release is limited by the reactivity of arsenic-bearing iron oxides with respect to native organic carbon, but equally limited by organic carbon reactivity with respect to the native arsenic-bearing iron oxides