We have developed an analytical method for detection of239Pu in aqueous samples at concentrations as low as 10–10M. This nuclear counting technique utilizes the uranium L X-rays, which follow the alpha-decay of plutonium. Because L X-rays are specific for the element and not for the individual isotope, the isotopic composition of the plutonium sample must be known. The counting efficiency in the 11–23 keV range is determined from a plutonium standard, and the concentration of the sample is then calculated from the L X-ray count and the isotopic composition. The total L X-ray count is corrected for possible contributions from other radionuclides present as impurities by measuring the low-energy gamma-spectrum for each contaminant to establish specific photon/X-ray ratios. The ratios are important when241Pu and242Pu are measured, because the respective decay chain members produce non-U L X-rays. This new method can replace the use of labor-intensive radiochemical separation techniques and elaborate activation methods for analysis of239Pu in aqueous samples. It is also applicable for assaying plutonium in liquid wastes that pose possible hazards to the environment.
A scheme was developed for the determination of oxidation states of plutonium in environmental samples. The method involves a combination of solvent extractions and coprecipitation. It was tested on solutions with both high-level and trace-level concentrations. The scheme was used to determine Pu oxidation states in solutions from solubility experiments in groundwater from a potential nuclear waste disposal site. At steady-state conditions, Pu was found to be soluble predominantly as Pu(V) and Pu(VI).
Authors:A. Catorci, S. Cesaretti, R. Gatti, and G. Ottaviani
The present research deals with the impact of the invasive species Brachypodium genuense in central Apennine meadows. The study compares meadows under different management types (mown versus abandoned). B. genuense spread in the abandoned condition alters the ecological status of the site. It lowers soil temperature, moisture and pH, while it increases soil C/N ratio and litter production. In terms of biotic features, phenological analysis indicated that the abandoned condition is less rich in flowering species and individuals in each analysed date. We observed a less affected temporal niche (during the first phase of B. genuense leaf growth) and two strongly influenced phases (in early spring and in correspondence with phases when B. genuense flowers and has full growth of leaves). Functional trait analysis indicated that species with runners, ability to form patches, and late flowering strategies benefit from B. genuense spread, whereas species marked by storage organs, small size, and early flowering strategies benefit in the mown condition. However, it seems that only low frequency species are heavily threatened, while the others can remain inside the plant community by shelter niche occupation.