排序方式: 共有27条查询结果,搜索用时 15 毫秒
21.
Mahmoud Joe Higginson Matthew Gilligan Christopher Thompson Paul Livens Francis Heath Scott L. 《Journal of Radioanalytical and Nuclear Chemistry》2022,331(3):1353-1360
Journal of Radioanalytical and Nuclear Chemistry - A method for rapid separation of americium from complex matrices by use of two commercially available extraction chromatography resins is... 相似文献
22.
SCHNEIDER Dominique 《中国科学 数学(英文版)》2010,(3)
In order to study the recurrence of sequences of integers, we investigate their L2-exactness and Θ-Hartman property (Θ being a set of rational numbers). Two classes of sequences of integers are well studied, which are return times relative to a weakly mixing system and Bernoulli random sequences. 相似文献
23.
236U is produced only by neutron irradiation of uranium and therefore is potentially useful as a marker for anthropogenic uranium in the environment. Accelerator mass spectrometry (AMS) provides a technique for the determination of very low concentrations of actinide nuclides, and has now been applied to the determination of 236U:235U ratios in an intertidal sediment core collected from the North Irish Sea. Combining measurements of the 238U mass concentrations calculated from alpha spectrometry with 238U:235U ratios from ICP-MS and 236U:235U ratios from AMS has allowed the estimation of the mass concentrations of 236U in the sediments. 236U mass concentrations are in the range 10(-8) to 10(-9) g kg-1, and 236U:238U atom ratios in the range from 10(-5) to 10(-6), well above natural baseline levels. Uncertainties based on propagation of measurement errors were less than +/- 10% although +/- 15% is perhaps a more realistic estimate of overall uncertainty. 相似文献
24.
D L Singleton F R Livens N A Beresford B J Howard C L Barnett R W Mayes M G Segal 《The Analyst》1992,117(3):505-509
A simple extraction procedure has been developed to assess rapidly the probable extent of the transfer of radiocaesium into ruminant food products soon after a nuclear accident. The in vitro extractions were validated against true absorption measurements of different forms of radiocaesium in the sheep gut. Extractions were performed on a range of different radiocaesium sources. Some of these sources were artificial (ionic radiocaesium adsorbed onto bentonite, silica spheres and filter-papers) and others were environmentally contaminated [silt from the Ravenglass Estuary contaminated by effluent from British Nuclear Fuels Limited (BNFL) Sellafield, and upland grass and heather contaminated by Chernobyl fallout]. Laboratory experiments concentrated primarily on the use of simple inorganic extractants in competitive ion-exchange processes. Of the reagents used, 0.1 mol dm-3 stable caesium chloride solution was the most effective extractant. The proportion of radiocaesium extracted by 0.1 mol dm-3 caesium chloride correlated well with measurements of true absorption. Extracting radiocaesium using 0.1 mol dm-3 caesium chloride proved to be an inexpensive and rapid method of predicting the availability of radiocaesium for absorption in the ruminant gut, giving results within 24 h. Further extractions were carried out using cellulase/pepsin simulated digestions and ovine rumen fluid. Results suggested that the availability of radiocaesium from some inorganic sources may be underestimated using such techniques. 相似文献
25.
N. D. Bryan F. R. Livens A. D. Horrill 《Journal of Radioanalytical and Nuclear Chemistry》1994,182(2):359-366
Field observations suggest that plutonium and americium in the environment are present in very different chemical forms in the interstitial waters of an intertidal sediment. Themodynamic modelling using the PHREEQE code predicts that plutonium is present entirely in oxidation state (V) as the PuO2CO
3
–
ion, whereas americium is present entirely in oxidation state (III), largely as the uncharged Am(OH)CO3 species, but with significant concentrations of the Am3+ and the AmSO
4
+
ions. There are, however, differences between these predictions and others published for a very similar system which apparently arise from uncertainties in the thermodynamic data. Field data cannot resolve these differences unambiguously. 相似文献
26.
Garcia-Pablos D Sigalas M Montero De Espinosa FR Torres M Kafesaki M Garcia N 《Physical review letters》2000,84(19):4349-4352
We study elastic band gaps in nonhomogeneous periodic finite media. The finite-difference time-domain method is used for the first time in the field of elastic band-gap materials. It is used to interpret experimental data for two-dimensional systems consisting of cylinders of fluids (Hg, air, and oil) inserted periodically in a finite slab of aluminum host. The method provides good convergence, can be applied to realistic finite composite slabs, even to composites with a huge contrast in the elastic parameters of their components, and describes well the experiments. 相似文献
27.
Investigation of ligand exchange reactions in aqueous uranyl carbonate complexes using computational approaches 总被引:1,自引:0,他引:1
Doudou S Arumugam K Vaughan DJ Livens FR Burton NA 《Physical chemistry chemical physics : PCCP》2011,13(23):11402-11411
Carbonate anion exchange reactions with water in the uranyl-carbonate and calcium-uranyl-carbonate aqueous systems have been investigated using computational methods. Classical molecular dynamics (MD) simulations with the umbrella sampling technique were employed to determine potentials of mean force for the exchange reactions of water and carbonate. The presence of calcium counter-ions is predicted to increase the stability of the uranyl-carbonate species in accordance with previous experimental observations. However, the free energy barrier to carbonate exchange with water is found to be comparable both in the presence and absence of calcium cations. Possible implications of these results for uranyl adsorption on mineral surfaces are discussed. Density functional theory (DFT) calculations were also used to confirm the trends observed in classical molecular dynamics simulations and to corroborate the validity of the potential parameters employed in the MD scheme. 相似文献