Isotope analysis | EPFL Graph Search

Isotope analysis is the identification of isotopic signature, abundance of certain stable isotopes of chemical elements within organic and inorganic compounds. Isotopic analysis can be used to understand the flow of energy through a food web, to reconstruct past environmental and climatic conditions, to investigate human and animal diets, for food authentification, and a variety of other physical, geological, palaeontological and chemical processes. Stable isotope ratios are measured using mass spectrometry, which separates the different isotopes of an element on the basis of their mass-to-charge ratio. Tissues affected Isotopic oxygen is incorporated into the body primarily through ingestion at which point it is used in the formation of, for archaeological purposes, bones and teeth. The oxygen is incorporated into the hydroxylcarbonic apatite of bone and tooth enamel. Bone is continually remodelled throughout the lifetime of an individual. Although the rate of turnover of

Shape staggering of midshell mercury isotopes from in-source laser spectroscopy compared with density-functional-theory and Monte Carlo shell-model calculations

Neutron-deficient Hg177-185 isotopes were studied using in-source laser resonance-ionization spectroscopy at the CERN-ISOLDE radioactive ion-beam facility in an experiment combining different detection methods tailored to the studied isotopes. These include either alpha-decay tagging or multireflection time-of-flight gating for isotope identification. The endpoint of the odd-even nuclear shape staggering in mercury was observed directly by measuring for the first time the isotope shifts and hyperfine structures of Hg177-185. Changes in the meansquare charge radii for all mentioned isotopes, magnetic dipole, and electric quadrupole moments of the odd-A isotopes and arguments in favor of I = 7/2 spin assignment for Hg-177,Hg-179 were deduced. Experimental results are compared with density functional theory (DFT) and Monte Carlo shell model (MCSM) calculations. DFT calculations using Skyrme parametrizations predict a jump in the charge radius around the neutron N = 104 midshell, with an odd-even staggering pattern related to the coexistence of nearly degenerate oblate and prolate minima This near-degeneracy is highly sensitive to many aspects of the effective interaction, a fact that renders perfect agreement with experiments out of reach for current functionals. Despite this inherent difficulty, the SLy5s1 and a modified UNEDF1(SO) parametrization predict a qualitatively correct staggering that is off by two neutron numbers. MCSM calculations of states with the experimental spins and parities show good agreement for both electromagnetic moments and the observed charge radii. A clear mechanism for the origin of shape staggering within this context is identified: a substantial change in occupancy of the proton pi h(9/2) and neutron nu i(13/2) orbitals.

AMER PHYSICAL SOC2019

Assessment of the water resource in Tambarga (Burkina Faso) based on stable isotope analysis

Tabea Schutter

Assessment of available water is the basis that allows for sustainable management of the water resource. Special need concerns the assessment of groundwater resources, about which, often little is known. The present study aims to explore the water resource, with a focus on groundwater, of a small catchment (3.5km2), situated in a semi-arid zone in Burkina Faso (West Africa). A 5-year data set of stable isotopes of water, groundwater level and other hydrologic data is used to gain insight into the water resources in this small catchment. The main effort is devoted to the analysis of isotope data, with the secondary goal to asses the potential of the use of stable isotopes of water as an innovative tool in hydrology. Analyzed are temporal and spacial variations of the isotopic signature in groundwater, surface water and rain. Isotope data is compared to groundwater level data. Isotope data allowed to distinguish two different categories of wells. First, wells where evaporation dominated compared to recharge at the end of the wet season through the dry season, and wells that have constant isotope ratios throughout the year. Evolution of the isotope signature of the former suggests that these wells get disconnected from the aquifer at some point of the year. Comparison of isotope ratios of different sampling sites (springs, wells, pumps, surface water and rain) revealed that the upstream springs diverge from the other sites in their isotopic signature, and thus either have a different origin or were subject to different processes. Negligible diurnal variations observed in isotopic signatures of wells prompt that diurnal fluctuations observed in groundwater levels are due to non isotope fractionation processes. Periods deduced from seasonal changes in isotopic signatures match periods of rising and decreasing groundwater levels. Though groundwater levels show inter-annual variability, especially in their peak levels, this was not reflected in the isotope data. Isotope data confirmed conclusions gained from other data (recharge periods), added additional information (diurnal fluctuations of wells are non isotope fractionation processes), and pointed out the fact that upstream spring water distinguishes in some form or another from other groundwater.

2014

Anaerobic degradation of vinyl chloride in aquifer microcosms

Christof Holliger

The anaerobic degradation potential at a chloroethene-contaminated site was investigated by operating two anoxic column aquifer microcosms enriched in iron(III). One column was fed with vinyl chloride (VC) only (column A) and one with acetate in addition (column B). In column A, after about 600 pore volume exchanges (PVEs) VC started to disappear and reached almost zero VC recovery in the effluent after 1000 PVEs. No formation of ethene was observed. In column B, effluent VC was almost always only a fraction of influent VC. Formation of ethene was observed after 800 PVEs and started to become an important degradation product after 1550 PVEs. However, ethene was never observed in stoichiometric amounts compared with disappeared VC. The average stable isotope enrichment factor for VC disappearance in column A was determined to be -4.3‰. In column B the isotope enrichment factor shifted from -10.7 to -18.5‰ concurrent with an increase in ethene production. Batch microcosms inoculated with column material showed similar isotope enrichment factors as the column microcosms. These results indicated that two degradation processes occurred, one in column A and two in parallel in column B with increasing importance of reductive dechlorination with time. This study suggests that in addition to reductive dechlorination other degradation processes such as anaerobic oxidation should be taken into account when evaluating natural attenuation of VC and that isotope analysis can help to differentiate between different pathways of VC removal.

American Society of Agronomy2011

Assessment of the water resource in Tambarga (Burkina Faso) based on stable isotope analysis

Tabea Schutter

2014