Li Distribution Research Articles

Lithium in stars with exoplanets

We present a comparison of the lithium abundances of stars with and without planetary-mass companions. New lithium abundances are reported in 79 planet hosts and 38 stars from a comparison sample. When the Li abundances of planet host stars are compared with the 157 stars in the sample of field stars of Chen et al. ([CITE]) we find that the Li abundance distribution is significantly different, and that there is a possible excess of Li depletion in planet host stars with effective temperatures in the range 5600–5850 K, whereas we find no significant differences in the temperature range 5850–6350 K. We have searched for statistically significant correlations between the Li abundance of parent stars and various parameters of the planetary companions. We do not find any strong correlation, although there are may be a hint of a possible gap in the Li distribution of massive planet host stars.

Lithium in the Open Cluster NGC 6475

We present the results of a lithium study of the 220 Myr old cluster NGC 6475. Our data are merged with those from previous Li surveys of this cluster in order to construct a more statistically significant sample. The Li vs. effective temperature distribution of the merged sample is compared with the one of the co-eval, but more metal poor cluster M 34 and with the ones of the younger Pleiades and older Hyades. The results are discussed in the framework of non-standard Li depletion on the main-sequence between the age of the Pleiades (˜ 120 Myr) and that of the Hyades (˜ 600 Myr).

Tomographic study of the three-dimensional distribution of a high-fluence implant in a polymer

Li+ ions were implanted into PMMA at high flux up to fluences of 1×1015 cm-2 under angles of 0° to 70° towards the surface normal. The Li depth distributions were determined by means of neutron depth profiling, and compared with theoretical simulations. The three-dimensional Li distribution was reconstructed from the one-dimensional depth profiles by means of a tomographic technique.

Surface profiling of lithium with a laser-desorption mass-spectrometer microprobe

A laser-desorption mass-spectrometer microprobe has been developed to profile Li distributions on the crevice surfaces of Cr-plated rolled-joint hubs. A single laser pulse is used to desorb and ionize the surface species followed by detection of Li(+) in a time-of-flight mass spectrometer. Images of the surface Li distribution are obtained with a resolution of <10 microm. These images are directly compared with Li images from the more conventional secondary ion mass spectrometry technique and evaluated with respect to surface topographical features measured by secondary electron microscopy and atomic force microscopy. The laser-desorption images are shown to provide the same qualitative information as that available from secondary ion mass spectrometry.

LITHIUM CONTENTS IN MANTLE PERIDOTITES AND PYROXENITES: AN INDICATOR FOR MAGMATIC AND METASOMATIC PROCESSES

In the search for a reliable indicator of chemical processes in the Earth’s mantle, we have undertaken a study of the Lithium contents in mantle minerals. The motivation behind this investigation is that Li is a relatively mobile alkali metal on the one hand, but its small ionic radius makes it only a moderately incompatible element (e.g., Blundy & Wood, 1994). Such characteristics could make Li a sensitive indicator of metasomatic or magmatic processes. To test this hypothesis, we have measured Li concentrations in orthopyroxene, clinopyroxene, olivine, garnet and spinel from two suites of spinel peridotites, garnet peridotites and garnet pyroxenites; one suite comprises xenoliths that are very well equilibrated in terms of major and a number or minor and trace elements, and the other suite is composed of samples for which there is clear evidence of metasomatism. The metasomatised samples are from several orogenic lherzolite massifs in the French Pyrenees and the Ivrea Zone (Italy) as well as being xenoliths from Victoria, Australia. The Li concentrations were measured using an ion microprobe (SIMS). The suite of equilibrated samples indicates that Li is preferentially incorporated into olivine, (1-2 ppm) with lesser concentrations (100s of ppb) in both clinopyroxene and orthopyroxene. The Li contents of garnet and spinel are at or near to the detection level (» 10 ppb). The following partitioning relationships are valid for peridotite and pyroxenite bulk compositions respectively: ol>cpx³opx>>gt,sp and cpx³opx>>gt. Of particular importance is the observation that the intercrystalline partitioning of Li between these phases is basically independent of temperature and pressure and chemistry, within the limits of such mantle bulk compositions. Combining our results with modal abundances for the samples, the bulk Li content for fertile to moderately depleted lithospheric mantle is 1-1.5 ppm, which is in excellent agreement with other previous estimates for primitive mantle (Jagoutz et al., 1979; Frey et al., 1985; Ryan and Langmuir, 1987; O’Neill, 1991; McDonough and Sun, 1995). Both the peridotites and pyroxenites display variations in absolute Li abundances, although the partitioning relationships between olivine, clinopyroxene and orthopyroxene are maintained. Lower overall Li abundances in peridotites are consistent with depletion from partial melting and subsequent melt extraction. The pyroxenes in the pyroxenites have variable Li contents with values typically of 1-3 ppm. This is consistent with their origin as cumulates. Some samples have elevated Li contents, which could be due to a higher degree of trapped melt present during crystallisation. Thus the greater variation in Li contents in the pyroxenites can be explained by variable degrees of trapped melt associated with the cumulate crystals, which themselves have relatively low Li concentrations due to the expected melt/solid partitioning behaviour of Li. The Li contents of the metasomatised samples are generally higher than those observed in the equilibrated samples and usually display much more variability within a single sample. Olivine and/or clinopyroxene can contain in excess of 5 ppm Li in these metasomatised samples. Modal metasomatic phases, such as amphibole and phlogopite also contain Li, but often in concentrations less than in the coexisting olivine or clinopyroxene. Analysis of a hornblendite dike from the Lherz massif indicates that Li is preferentially partitioned into phlogopite compared with amphibole. The most notable feature of the metasomatised samples is that most record a disequilibrium distribution of Li between olivine and the coexisting pyroxenes. Preferential enrichment of Li can occur in either olivine or clinopyroxene apparently depending on the type of metasomatising agent; olivine is preferentially enriched in samples from Victoria, which have been affected by carbonatitic melts and clinopyroxenes are preferntially enriched in samples that have interacted with mafic silicate melts. Samples from Finero (Italy), that apparently interacted with fluids, also Li distributions indicative of moderate disequilibrium. The partitioning of Li between olivine and the pyroxenes provides an additional indicator for recognising cryptic metasomatism. Given the correct conditions (a high enough temperature, long enough time for reaction etc..), an equilibrium distribution can be achieved in metasomatised samples, however, these will still display an overall enrichment in Li compared to ‘normal’ mantle values.

Time-of-flight neutron diffraction study on the cryolite type phases of Li 6NBr 3

A hitherto unknown Li-ordered variant Li 6NBr 3I′ has been obtained from Li-disordered Li 6NBr 31 on cooling. I′ is stable only over a restricted temperature range from −60 to −80°. Its structure has been solved from neutron powder diffraction data collected using the high resolution powder diffractometer (HRPD) at the spallation source ISIS, UK. Li 6NBr 3I′ crystallizes in the space group P2 1/n (No. 14) a = 6.26585(4), b = 6.29839(4), c = 8.95577(6) pm, β = 90.171(1)° with two formula units per unit cell. Its structure is an antitype of that of the mineral cryolite, Na 3AlF 6. The characteristic structural unit is a distorted NLi 6 octahedron approximating D 2h symmetry with an average LiN bondlength of 192.7 pm. The distortion from O h symmetry manifests in one LiNLi bondangle being significantly smaller than 90°, most likely arising from packing effects. The structure of Li-disordered Li 6NBr 3I has been redetermined. The improved Li distribution obtained is shown to be in agreement with orientationally disordered NLi 6 octahedra.

Fluid inclusions in the Harney Peak Granite, Black Hills, South Dakota, USA: Implications for solubility and evolution of magmatic volatiles and crystallization of leucogranite magmas

Experimental and theoretical studies have shown that magmatic fluids have strong influence on phase equilibria of granitic systems. A microthermometric study of fluid inclusions in the Proterozoic Harney Peak Granite, Black Hills, South Dakota, USA, was undertaken to obtain direct evidence for the composition and evolution of magmatic fluids in a leucogranitic system and to evaluate their effect on liquid-lines-of-descent of leucogranite magmas. A previous stable isotopic study has demonstrated that the granite has not interacted with nonmagmatic fluids since its crystallization. Therefore, fluids found in the inclusions are of magmatic origin and present an opportunity to directly sample magmatic fluids trapped during crystallization of a granitic magma and during subsolidus conditions. The Harney Peak Granite was emplaced as multiple sills, dikes, and small intrusions, many of which differentiated into coupled aplite-pegmatite layers. Three types of fluid inclusions are found in the granite. Type 1 consist of variable saline H 2OC0 2 mixtures with minor CH 4 or other gases. Inclusions of this type are found in tourmaline and quartz in aplite layers, are generally isolated, and have negative crystal shapes. They are interpreted to be primary. There is a general increase in salinity and decrease in isochore temperature with decreasing CO 2/H 2O ratio of the inclusions. The trend is ascribed to progressive change in fluid composition with crystallization due to the differential solubility of CO 2 and H 2O in the high-silica magma. Isochores, coupled with independently determined crystallization temperatures, suggest entrapment pressure ∼3.5 kbar, consistent with geobarometry in the wallrocks. Type 2 inclusions are carbonic fluids dominated by CO 2, whereas type 3 inclusions are saline aqueous fluids without a detected carbonic component. Both types are mostly found along healed fractures in quartz. They are interpreted to be secondary inclusions that formed as a result of unmixing of type 1 inclusions at subsolidus conditions during uplift and cooling of the Harney Peak Granite dome. Freezing-point depressions, birefringent daughter crystals, phase-equilibria considerations, and α-track mapping of B and Li distribution in thin sections, all indicate that both type 1 and type 3 inclusions contain solutes such as K, Li, and B in addition to NaCl. Using published solubility models for H 2O and CO 2 in granitic melts and the composition of the most CO 2-rich type 1 inclusions ( X CO 2 = 0.55), the initial H 2O and CO 2 concentrations in the Harney Peak Granite magma are deduced to have been ∼3.5 wt% and 1500 ppm, respectively. The relatively low water concentration is consistent with temperatures of dehydration-melting reactions that produced the magma. It is suggested that the aplite-pegmatite segregations found in parts of the Harney Peak Granite are the result of initial rapid near liquidus crystallization of minerals with high Na/K ratios, including plagioclase and tourmaline, along a wide range of increasing αH 2O. Aplite crystallization was followed by crystallization of relatively potassic residual liquid enriched in fluxing elements under conditions of high αH 2O.

Influence of energetic ions on grafting to polyethylene

Li salts of acrylic acid were grafted to polyethylene, PE. It is known that li is mobile in this material at room temperature, and hence can act as a probe for newly introduced defects. After irradiation of PE(Li) with 100 keV He+ ions at different fluences the Li depth distributions were measured by NDP. Changes in the Li distributions are observed which are ascribed to bonding at oxygen, the latter one preferentially penetrating into the PE via the irradiation-damaged sample surface. With increasing sample age, i.e. after exposure to ambient atmosphere for more than half a year, Li appears to lose its original mobility.

On the redistribution of6Li + ions implanted into polypropylene foils

6Li+ (150 keV) was implanted into thin polypropylene foils at fluences of 1 x 1013 to 1 x 1014 cm−2. Subsequent neutron depth profiling measurements of the Li distributions revealed considerable deviations from the expected ballistic range profiles. This Li redistribution was simulated by a numerical computer calculation. The best fit between measurements and simulations was obtained by assuming that (i) Li redistributes immediately after its ballistic slowing-down, (ii) the Li mobility is enhanced in the radiation-damaged polymer region, the local diffusion enhancement being controlled by the target's electronic damage, (iii) mobile Li is readily trapped at radiation-induced defects, their density being proportional to the target's electronic damage, (iv) these traps are saturable ones, and (v) Li migration is not restricted to the ion track region, but proceeds also through the neighboring unirradiated bulk, though with slower speed.

B and Li distribution in the Pena Negra Complex; an alpha-track study

B and Li distribution in the Pena Negra Complex; an alpha-track study

Depth Distribution of Lithium in Oxidized Binary Al-Li Alloys Determined by Secondary Ion Mass Spectrometry and Neutron Depth Profiling

Abstract Oxidation of binary Al-Li alloys during short exposures at 530°C and long exposures at 200°C was studied with regard to the Li distribution. Secondary ion mass spectrometry (SIMS) and neut...

In vivo 7Li NMR imaging and localized spectroscopy of rat brain.

Lithium-7 in vivo NMR spectroscopy and imaging techniques have been developed at 4.7 T for rat head. The pharmacokinetics of lithium (Li) uptake in rat head has been measured using STEAM localized spectroscopy for the whole brain, which showed relatively rapid uptake of Li and a steady level of Li from about 5 to 20 h. Localized spectroscopy on brain sections revealed no differences in Li concentration among the front, middle, and rear of the brain. The spin-lattice relaxation time showed a single exponential decay for the head. The spin-spin relaxation time for head showed a biexponential behavior. Using a 1H-7Li double coil assembly, 7Li images were generated for rat head, as was the corresponding 1H image for anatomic localization. The 7Li image (7-mm slice thickness, 4-mm in-plane resolution) recorded after the last dose in a multiple ip dose protocol shows the Li distribution in the head and neck. Based on 7Li images, the Li level in muscle was about twice that in the brain. Variations of 7Li intensity level across the brain were typically small.

Investigation of Li distribution in aluminium alloy welds by elemental radiographic analysis

The lithium distribution in welded joints of aluminium-, magnesium-, and lithium-based materials has been studied by the (n, α)-radiography technique. Metallographic thin sections of welded cross-sections have been chosen as research subjects. It has been found that isothermal annealing, following welding, results in the redistribution of the lithium concentration gradient in the weld area and also leads to an improvement of the quality of the welded joint.

Effects of lithium doping on the formation and microstructure of bulk Bi [sbnd]Sr [sbnd]Ca [sbnd]Cu [sbnd

The effects of Li doping on Bi 2 Sr 2 CaCu 2 O x pellets has been studied by considering Li substitution for Sr and Cu and Li additions to stoichiometric Bi 2 Sr 2 CaCu 2 O x . As the Li substitution reduces the melting temperature by as much as 160°C, melting studies were performed to determine the sintering conditions for melt-quenching. While a variety of stoichiometries all exhibited S N transitions above 80 K, the transition of Bi 2 Sr 2 Ca(Cu 0.55 Li 0.45 ) 2 O x was significantly narrower than other cation combinations. However, Li did not increase T c relative to Bi 2 Sr 2 CaCu 2 O x [1–4]. Microstructural analysis by SEM and SIMS indicated that the Bi, Sr, Ca and Cu are all distributed uniformly throughout the pellet, while the Li distribution is quite inhomogeneous. Furthermore, SIMS depth profiling into the Ag/BSCCOLi interface showed that although the Bi:Sr:Ca:Cu ratio remains relatively constant, the Bi:Li ratio increases by over 100%, indicating that the Li penetrates the Ag interface to a greater extent than the other cations and that Li doping may effect the behaviour at the BSCCO/Ag interface.

Secondary ion imaging of the distribution of δ′ (Al 3Li) in Al-Li alloys

A high resolution scanning ion microprobe has been used, in conjunction with transmission electron microscopy, to study the distribution of the metastable δ' (Al 3Li) phase in Al-Li alloys. Various secondary ions were used for chemical imaging (lateral resolution ∼ 80 nm) and their contrast aspects and formation mechanisms are discussed. δ' particles appeared dark in the 27Al +, 7Li + and 34AlLi + distribution maps despite their higher Li content than the α matrix (aluminum-lithium solid-solution). Maps generated from two molecular ions, 14Li + 2 and 41Li 2Al +, exhibited true chemical contrast in the images: the δ' precipitates appeared bright in accordance with the known Li distribution. Using retrospective image analysis, measurements were made of the secondary ion intensities displayed by the δ' particles and the α matrix. Efforts to calibrate the secondary ion intensities for quantitative analysis are also described. The unusual ion formation mechanism from δ' precipitates illustrates the coupled channel model of secondary particle emission: the observed favored emission of Li 2 causes Li emission to be depressed.

Analysis for lithium by secondary ion mass spectrometry (SIMS) on corroded steel surfaces

Abstract The steel AISI 316 is inert to the tritium breeders Li2O, Li2SiO3 and metallic Li except in the presence of impurities or at very high temperatures. Under these conditions the steel can be corroded severely, and SIMS is uniquely suitable for detecting the Li distribution. Corroded steel surfaces have been analysed by SIMS, and when the technique is complemented by Scanning Electron Microscopy with Energy Dispersive X-ray Analysis (SEM/EDAX), and X-Ray Diffraction (XRD), it is seen that both solid (Li2O, Li2SiO3) and liquid (Li) potential tritium breeders (for fusion devices) corrode the steel similarly. The steel is penetrated by Li+ ions together with the corresponding anions via grain boundaries and Cr is extracted from the grains to give Cr-depleted steel ( = Fe Ni ). A stable ternary compound (LiCrO2 with Li2O and Li2SiO3; Li9CrN5 with Li/Li3N) is formed in the grain boundaries and also as a layer on the steel surface. This type of corrosion alters the surface composition of the steel and the intergranular penetration is the precursor to steel fracture.

Effects of chronic lithium administration on brain weights, acetylcholinesterase activity and learning ability in rats

In order to test the effects of chronic lithium (Li) administration on learning and memory, 21 day old rats were subjected to different degrees of environmental stimulation (enriched condition, EC and impoverished condition, IC) with and without Li for 144 days. Li was administered with food (2.18 mEq/Kg weight/day). Average plasma Li concentration at the end of the experiment was 0.41 ± 0.04 μEq/ml. Both Li treatment and the environmental condition showed an overall significant effect on the cortex/subcortex weight ratio and learning ability index, but not on AChE activity in occipital cortex. A similar pattern of brain Li distribution was observed in both EC-Li and IC-Li, with occipital cortex having the highest levels. Li tissue/protein/plasma ratio was higher in EC than in IC, in all the brain areas studied. Other organs (liver and kidney) did not show EC-IC differences in the tissue/protein/plasma Li ratio.

A search for lithium-rich giant stars

Lithium abundances or upper limits have been determined for 644 bright G-K giant stars selected from the DDO photometric catalog. Two of these giants possess surface lithium abundances approaching the cosmic value of the interstellar medium and young main-sequence stars, and eight more giants have Li contents far in excess of standard predictions. At least some of these Li-rich giants are shown to be evolved to the stage of having convectively mixed envelopes, either from the direct evidence of low surface carbon isotope ratios, or from the indirect evidence of their H-R diagram positions. Suggestions are given for the unique conditions that might have allowed these stars to produce or accrete new lithium for their surface layers, or simply to preserve from destruction their initial lithium contents. The lithium abundance of the remaining stars demonstrates that giants only very rarely meet the expectations of standard first dredge-up theories; the average extra Li destruction required is about 1.5 dex. The evolutionary states of these giants and their average masses are discussed briefly, and the Li distribution of the giants is compared to predictions of Galactic chemical evolution. 110 refs.

Microanalysis of precipitates in aluminum-lithium alloys with a scanning ion microprobe

Scanning ion microscopy (SIM) and secondary ion mass spectrometry (SIMS) are uniquely suited to the study of aluminum-lithium alloys because of the intense Li + signal that is generated when high energy ions impinge on lithium-containing materials. We used a high-lateral-resolution scanning ion microprobe to determine the Li distribution in AlLi alloys containing less than about Li. In these alloys, the 7Li + signal-to-background ratio is about 10 5. We obtained 7Li +, 27Al + and 34(AlLi) + distribution images exhibiting better than 100 nm spatial resolution that show both the distribution of Li in binary alloys and the morphology of δ (AlLi phase) plates. For the first time, SIM images of coarse (∼ 100 nm δ′ (Al 3Li) precipitates were obtained by monitoring either the 27Al +, 7Li + or the 34(AlLi) + secondary ion signals and were compared directly with TEM images. These molecular ion signals can only be detected, without artifacts, in the complete absence of oxygen adsorbed on the alloy. Calibration data were obtained which form the basis for qualtitative Li measurement.

The measurement of the trace Li content and distribution in ZnO films and the thickness of these films

The content and distribution of trace Li in ZnO films and the thickness of these films have been determined with reaction 7Li (p,α) 4He. An approximate and simple method used to determine the content of the trace element by the yield of thin standard target at an average energy has been established. This average energy can be found from the spectrum of the emerging particle or from the Rutherford backscattering spectrum of incident protons.