Cr Isotopes Research Articles

Axial inductively coupled plasma time-of-flight mass spectrometry using direct liquid sample introduction

This report is concerned with the first investigation of a direct injection high efficiency nebulizer (DIHEN) as a microliter-solution introduction system for axial inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS). The effect of rf generator frequency on analytical performance indices is investigated at both 27 and 40 MHz at operating conditions suitable for the DIHEN: a solution uptake rate of 100 µL min−1, nebulizer gas flow rate of 0.2 L min−1, and rf power from 800 to 1700 W. Four observations indicate an increased secondary discharge at 27 MHz compared to 40 MHz for the DIHEN compared to conventional solution introduction: (1) higher background count rates, (2) faster and wider ion deflection pulse times, (3) increased doubly-to-singly charged ion ratios (Ba2+/Ba+ = 0.03 vs. 0.02), and (4) reduced oxide-to-metal ion ratios (CeO+/Ce+ = 8.5 vs. 51) at 27 MHz in comparison with 40 MHz. Analytical figures of merit achieved, including detection limits, sensitivity, and precision using DIHEN-ICP-TOFMS are superior in both normal and cool plasma conditions to those obtained with a conventional nebulizer-spray chamber arrangement operated at a solution uptake rate of 1 mL min−1. For example, typical precision (percent relative standard deviation, %RSD) for the DIHEN at 27 MHz is less than 0.6% for an integration time of 10 s. The signal intensity is nearly a factor of 2 higher with the DIHEN compared to the conventional nebulizer-spray chamber arrangement. Isotope ratio precision acquired by the DIHEN-ICP-TOFMS system closely approximates values predicted by Poisson counting statistics for both steady-state and transient signals. Finally, fast transient analysis (ca. 12.75 ms) is demonstrated for Sn and Cr isotopes in human lung fibroblast cells.

Effective interaction forpf-shell nuclei

An effective interaction is derived for use in the full $\mathrm{pf}$ basis. Starting from a realistic G-matrix interaction, 195 two-body matrix elements and four single-particle energies are determined by fitting to 699 energy data in the mass range 47--66. The derived interaction successfully describes various structures of $\mathrm{pf}$-shell nuclei. As examples, systematics of the energies of the first ${2}^{+}$ states in the Ca, Ti, Cr, Fe, and Ni isotope chains and energy levels of ${}^{56,57,58}\mathrm{Ni}$ are presented. The appearance of a new magic number 34 is seen.

Low-energy structure of neutron-rich Cr isotopes

Low-energy structure of neutron-rich Cr isotopes

Platinum-group elements in the Morokweng impact structure, South Africa: Evidence for the impact of a large ordinary chondrite projectile at the Jurassic-Cretaceous boundary

Radiometric dating of melt rocks at impact craters has revealed that some giant impacts appear to overlap in time with major boundaries in Earth history [e.g., the Cretaceous–Tertiary (K/T) and Jurassic–Cretaceous (J/K) boundaries]. The Morokweng impact crater in South Africa is coincident in age with the J/K boundary. However, the types of objects that generate large craters are poorly known because it is difficult to unambiguously identify the projectile from the signature it imparts into the impact rocks. Meteorites are highly enriched in the platinum-group elements (PGE), which have been widely used as a tool for identifying the presence of a meteorite signature. Here we present new PGE analyses from the Morokweng impact melt sheet. Our data reveal high PGE concentrations and high degree of PGE correlation through the melt sheet. Regression analysis was used to determine the projectile PGE signature and constrain input from the terrestrial target rocks. The closest match to Morokweng is the PGE signature of ordinary (L or LL) chondrite meteorites, which is broadly in agreement with the results of an earlier Cr isotope study. The results of these independent studies provide strong evidence that a large, ordinary chondrite projectile struck the area of Morokweng in the late Jurassic.

Analytical issues in nutritional chromium research

In most readily accessible biological samples from humans, like blood, serum/plasma, urine, etc, the levels of chromium (Cr) are less than 1 ng/g, and in many cases closer to 0.1 ng/g. Only 3 analytical techniques have the required sensitivity to make measurements at these levels, namely, neutron activation analysis (NAA), mass spectrometry (MS), and graphite furnace atomic absorption spectrometry (GFAAS). The first 2 are not widely available, and the third is the one most susceptible to interferences from the sample matrix. At the sub-parts-per-billion level, collecting samples without contaminating them and generating sufficiently low analytical and reagent blanks become extremely important and difficult. For other determinations of Cr, eg, in diet components, foods and tissues, where the levels are often well above the ng/g level, the required sensitivity is less of a limitation, but contamination problems remain, and factors like sample processing and homogeneity become more important. Problems and precautions in Cr determinations are discussed, and means of accuracy verification are presented. A novel use of stable isotopes of Cr in an accurate, non-radioactive method of measuring blood volume is described, as well as a discussion of the future of Cr determinations using inductively-coupled plasma mass spectrometry. J. Trace Elem. Exp. Med. 12:99–109, 1999. Published 1999 Wiley-Liss, Inc.

Analytical issues in nutritional chromium research

In most readily accessible biological samples from humans, like blood, serum/plasma, urine, etc, the levels of chromium (Cr) are less than 1 ng/g, and in many cases closer to 0.1 ng/g. Only 3 analytical techniques have the required sensitivity to make measurements at these levels, namely, neutron activation analysis (NAA), mass spectrometry (MS), and graphite furnace atomic absorption spectrometry (GFAAS). The first 2 are not widely available, and the third is the one most susceptible to interferences from the sample matrix. At the sub-parts-per-billion level, collecting samples without contaminating them and generating sufficiently low analytical and reagent blanks become extremely important and difficult. For other determinations of Cr, eg, in diet components, foods and tissues, where the levels are often well above the ng/g level, the required sensitivity is less of a limitation, but contamination problems remain, and factors like sample processing and homogeneity become more important. Problems and precautions in Cr determinations are discussed, and means of accuracy verification are presented. A novel use of stable isotopes of Cr in an accurate, non-radioactive method of measuring blood volume is described, as well as a discussion of the future of Cr determinations using inductively-coupled plasma mass spectrometry. J. Trace Elem. Exp. Med. 12:99–109, 1999. Published 1999 Wiley-Liss, Inc.

Electron paramagnetic resonance and photoluminescence studies of chromium in SrS

Isotropic features with hyperfine structures in electron paramagnetic resonance spectra of SrS powder phosphors, which reflect the abundance of the natural Cr isotopes, are attributed to the isolated Cr impurity. The isotropy, which is typical for a A24 ground state of a 3d3 ion in an octahedral crystal field, and the g value of 1.9795 verify that Cr is observed in its charged donor state Cr3+. The observation of a broad photoluminescence band with a maximum at 900 nm, which can be attributed to an internal Cr3+ transition, supports the identification of the impurity as Cr3+.

ESR Studies of Oxochromium(V) Porphyrin Complexes: Electronic Structure of the Cr(V)=O Moiety.

ESR spectra of oxochromium(V) porphyrins were obtained to investigate the electronic structure of the Cr(V)=O moiety. At room temperature, the chlorooxochromium(V) meso-tetramesitylporphyrin complex 1-Cl exhibits an isotropic ESR signal, split into nine signals due to hyperfine coupling with four equivalent( 14)N, at g = 1.982. A small isotropic satellite signal, split into a quartet due to hyperfine coupling by the (53)Cr isotope is also observed. At 77 K, 1-Cl shows an anisotropic ESR signal with g( parallel) = 1.986 and g( perpendicular) = 1.980 and small satellite g( parallel) signals arising from hyperfine coupling with the (53)Cr isotope. The ESR parameters of 1-Cl, obtained from ESR spectral simulation, show that the pi-bonding character of the Cr(V)=O bond is not as strong as that of the Cr(V)&tbd1;N bond. To explore substituent effects on the bond character of the Cr(V)=O moiety, ESR spectra of perchloratooxochromium(V) porphyrins having various electronegative substituents were recorded. With an increase in electronegativity of the meso-substituent, the g( perpendicular) value and the (53)Cr hyperfine coupling constant (|a((53)Cr)|) are increased. These changes suggest an increase in the pi-bonding character of the Cr(V)=O moiety with an increase in the electronegativity of the meso-substituent. Furthermore, the hyperfine coupling constant of the oxo ligand, |a((17)O)|, obtained from ESR spectra of (17)O-labeled oxochromium(V) porphyrin is increased with an increase in electronegativity of the meso-substituent. This indicates that the radical character of the oxo ligand is increased by the electronegative meso-substituent. These data suggest that the pi-antibonding orbital of Cr=O is destabilized with an increase in electronegativity of the meso-substituent, which may facilitate bond breaking of the Cr=O moiety in an epoxidation reaction.

Manganese‐chromium systematics in sulfides of unequilibrated enstatite chondrites

Abstract— We measured with a secondary ion mass spectrometer Mn/Cr ratios and Cr isotopes in individual grains of Mn‐bearing sulfides (i.e., sphalerites, ZnS; alabandites, MnS; and niningerites, MgS) in nine unequilibrated enstatite chondrites (UECs). The goals were to determine whether live 53Mn (half‐life ∼3.7 Ma) was incorporated in these objects at the time of their isotopic closure and to establish whether Mn‐Cr systematics in sulfides in UECs can be used as a high‐resolution chronometer to constrain formation time differences between these meteorites. Sulfide grains analysed in four of these UECs, MAC 88136 (EL3), MAC 88184 (EL3), MAC 88180 (EL3), and Indarch (EH4), have clear 53Cr excesses. These 53Cr excesses can be very large (δ53Cr/52Cr ranges up to ∼18,400%, the largest 53Cr excess measured so far) and, in some grains, are well correlated with the Mn/Cr ratios. Thus, they were most likely produced by the in situ decay of 53Mn in the meteorite samples. In the remaining five meteorites, no detectable excesses of 53Cr were found, and only upper limits on the initial 53Mn/55Mn ratios could be established. The four meteorites with 53Cr excesses show variations in the inferred 53Mn/55Mn ratios in various sulfide grains of the same meteorite. The Mn‐Cr systematics in these sulfides were disturbed (during and/or after the decay of 53Mn) by varying degrees of reequilibration. Provided 53Mn was homogeneously distributed in the region of the early solar system where these objects formed, the data suggest that the time of the last isotopic equilibration of sulfides in EL chondrites occurred at least 3 Ma after a similar episode in EH chondrites.

Fullpfshell study ofA=47andA=49nuclei

Complete diagonalizations in the $\mathrm{pf}$ major shell lead to very good agreement with the experimental data (level schemes, transitions rates, and static moments) for the $A=47$ and $A=49$ isotopes of Ca, Sc, Ti, V, Cr, and Mn. Gamow-Teller and $M1$ strength functions are calculated. The necessary monopole modifications to the realistic interactions are shown to be critically tested by the spectroscopic factors for one particle transfer from ${}^{48}$Ca, reproduced in detail by the calculations. The collective behavior of ${}^{47}$Ti, and of the mirror pairs ${}^{47}$V-${}^{47}$Cr and ${}^{49}$Cr-${}^{49}$Mn is found to follow at low spins the particle plus rotor model. It is then analyzed in terms of the approximate quasi-SU(3) symmetry, for which some new results are given.

Determination of cross section of α-induced nuclear reaction on natural Cr and Zr by stacked foil activation for thin layer activation analysis

The cross sections of different α-induced nuclear reactions on natural chromium and zirconium have been determined at different energies of the α-particles by the stacked foil activation technique using the 40 MeV α-beam from Variable Energy Cyclotron at Calcutta. The reaction channels studied from the stable isotopes of natural Cr and Zr are (α, xn), (α, p), (α, p xn) and (α, αn) (where x = 1 and 2). The excitation functions have also been reported for the energy range from 10 to 40 MeV of α-particles. The experimentally determined cross sections have been compared with the theoretical values computed on the basis of the hybrid model using a program ALICE 85/300. The analytical validation of the experimental values has been carried out with a vanadium target for which cross sections are already reported in the literature. The purpose of generating of the above cross sections is to support the thin layer activation technique for the study of surface wear in Cr and Zr based metals/alloys.

Finite-size effects in the gap equation for Paris interaction

Abstract The pairing problem in nuclei is approached starting from a realistic nucleon-nucleon interaction and solving the full gap equation in a complete basis. To this purpose the original bare nucleon-nucleon interaction, a separable form of the Paris potential, in the 1 S 0 channel is first renormalized into a large spherical Woods-Saxon basis which includes single-particle levels up to 100 MeV. The corresponding matrix elements in the Woods-Saxon basis are then used to solve exactly the gap equation. Proton and neutron gaps are computed for Cr and Fe isotopes. Finite-size effects are evidenced.

Recoil implantation of radioactive transition metals and their investigation in silicon by deep-level transient spectroscopy

Radioactive isotopes are produced by nuclear reactions in a thin target foil. The recoiling products are directly implanted into samples mounted off-axis to the primary beam. Using proton or α beams and appropriate target foils, radioactive isotopes of Ti, V, Cr, Mn, and Co were implanted. The implantation parameters are presented and compared with other implantation techniques for radioactive isotopes. To demonstrate an application, a deep-level transient spectroscopy measurement on 48V in silicon is presented. Ti and V correlated band-gap levels were observed during the 48V decay.

Determination of hexavalent chromium in sludge incinerator emissions using ion chromatography and inductively coupled plasma mass spectrometry

A unique approach is described using ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) for the determination of hexavalent chromium [Cr(VI)] in wastewater sludge incinerator emissions. Quartz fiber filters, spiked with an isotopically enriched ([sup 50]Cr or [sup 53]Cr) chromate salt, were used to collect emission particulates. The enriched Cr(VI) isotope was used to monitor the reduction of Cr(IV) during sample collection using a pseudo-first-order reaction model and to calculate the rate of deposition of native Cr(VI) on the filters. At the end of the sampling period, the Cr(VI) was extracted from the filters with 0.1 N sodium hydroxide and determined by IC using postcolumn derivatization with 1,5-diphenylcarbohydrazide. To determine the ratio of enriched Cr(VI) to the native Cr(VI) emitted from the incinerator, an additional aliquot of the sample extract was preconcentrated by IC and the isotopic composition of the Cr(VI) fraction determined by ICP-MS. 21 refs., 4 figs., 3 figs.

Zinc isotope anomalies in Allende meteorite inclusions

The isotopic compositions of Zn, Cr, Ti, and Ca have been measured in a number of CAIs from the Allende meteorite. The aim was to test astrophysical models which predict large excesses of Zn-66 to accompany excesses in the neutron-rich isotopes of Ca, Ti, Cr, and Ni. Some of the CAIs show clearly resolved but small excesses for Zn-66 which are at least an order of magnitude smaller than predicted. This result may simply reflect the volatility and chemical behavior of Zn as compared to the other (more refractory) anomalous elements found in these samples. Alternatively, revision of parameters and assumptions used for the model calculations may be required.

Chromium and titanium isotopes produced in photonuclear reactions of vanadium, revisited

Abstract Photonuclear production yields of 51 Ti und 51,49,48 Cr from 51 V were redetermined for bremsstrahlung end-point energies ( E 0 ) of 30 to 1000 or 1050 MeV with the aid of radiochemical separation of Cr. The yield curves for 51 Ti, 51 Cr, 49 Cr and 48 Cr show a clear evidence for two components in the production process; one tor secondary-proton reactions at E 0 Q π and the other for photopion reactions, at E 0 > Q , Q π being Q -values for (γ, π + ) and ( γ , π + x n) reactions. The contributions of the secondary reactions for production of the Ti and Cr isotopes at E 0 > Q π were then estimated by fitting calculated secondary yields to the observed ones at E 0 Q π , and found to be about 40%, 20%, 4% and 4% for 51 Ti, 51 Cr, 49 Cr and 48 Cr, respectively, at E 0 = 400 to 1000 MeV. The calculation of the secondary yields was based on the excitation functions for 51 V(n, p) and (p, x ′n) calculated with the ALICE code and the reported photoneutron and photoproton spectra from 12 C and some other complex nuclei. The present results for 49 Cr are close to the reported ones, while the present 48 Cr yields differ by a factor of about 50. For the 51 Ti and 51 Cr yields, there are some discrepancies between the present and reported ones. The yield corrected for the secondaries, in units of μb/equivalent quantum, were unfolded into cross sections per photon, in units of μb, as a function ol monochromatic photon energy with the LOUHI-82 code. The results for the 51 Ti and 49 Cr are in disagreement in both the magnitude and shape with the theoretical predictions based on DWIA and PWIA. A Monte Carlo calculation based on the PICA code by Gabriel and Alsmiller does reproduce the gross feature of the present results.

The identification of meteorite inclusions with isotope anomalies

Ca-Al refractory inclusions with characteristic chemical and mineralogical compositions show an enhanced occurrence of 20 pct of isotope anomalies reflecting unknown nucleosynthetic effects for O and Mg. The anomalies are characterized by large isotope fractionation in Mg, apparent deficits in Mg-26/Mg-24, and large correlated effects for isotopes of Ca, Ti, and Cr. These isotope patterns define exotic components depleted in the most neutron-rich isotopes of Ca, Ti, and Cr, or components depleted in isotopes produced in explosive O and Si burning. An opaque assemblage within one of the inclusions yields isotope anomalies in Cr similar to the bulk inclusion and must be intrinsically part of the inclusion and not a trapped, foreign grain aggregate.

Transport of Nickel and Oxygen during the Oxidation of Nickel and Dilute Nickel/Chromium Alloy

films have been grown on high‐purity Ni and Ni 0.1 weight percent (w/o) Cr alloy, at 700°C and 0.21 bar, by sequential oxidation in and . The distributions of oxygen, Ni, and Cr isotopes in the films were analyzed using SIMS. For both materials, the rate controlling transport process was found to be the outward diffusion of Ni through the . Inward oxygen gas transport also occurs and is responsible for the growth of new oxide within the films and for the growth of the inner layer of the well‐developed duplex films which grow on the alloy. A mechanism whereby oxygen gas penetrates the films through fissures to form new oxide in available space is proposed to explain the observations and the growth of duplex films.

Form factors and transition charge densities for the quadrupole and hexadecupole electroexcitation of some 2p-1f shell nuclei.

A microscopic description of the recent data on the inelastic electron scattering form factors for the 0/sup +/..-->..2/sup +/ as well as 0/sup +/..-->..4/sup +/ transitions in some doubly even Ti, Cr, Fe, Ni, and Zn isotopes is attempted in terms of the projected Hartree-Fock-Bogoliubov wave functions resulting from realistic effective interactions operating in the 2p-1f shell. It turns out that the available form factor data out to about 2.5 fm/sup -1/ can be reproduced in most of the cases in a fairly satisfactory manner in terms of reasonable values of effective charges. It is seen that the empirical transition charge densities in Ni and Zn isotopes extracted from the form factor data via the Fourier-Bessel analysis play a decisive role vis-a-vis the choice of a model of core-polarization contributions.

Response of Radioactive Trace Metals to Acid–Base Titrations in Controlled Experimental Ecosystems: Evaluation of Transport Parameters for Application to Whole-Lake Radiotracer Experiments

Radiotracer experiments were carried out in 20 enclosures located in two lakes at the Experimental Lakes Area (ELA), northwestern Ontario, to study pathways of trace metal removal from the water column of shallow lakes. Two removal mechanisms were characterized: (1) sorption to and subsequent transport with falling particles and (2) direct adsorption to surface sediments. Our approach was to measure independently the kinetics of radiotracer sorption, fluxes and concentrations for particles, particle settling velocities, and the "equivalent stagnant boundary film." Our radiotracer results enabled us to test the sensitivity of the tracer removal rates on these rate-determining processes using a numerical transport model. Acid titrations of whole ecosystems revealed that some trace metals (e.g. Mn, Co, and Zn) can diffuse back to the water column as the pH is lowered from 6.5 to 4.8 after 18 d, while others remain tightly bound (e.g. Sn, Fe, Se, Cr, Ag, and Hg isotopes). Subsequent CaCO3 additions to bring back the pH to its original value restored the initial removal conditions for acid-sensitive radiotracers, indicating that the pH sensitivity is reversible. Transport parameters for particle-related pathways or diffusive pathways across the sediment–water interface obtained from our enclosure experiments were used to predict the removal rates of "particle-reactive" 60Co and the "diffusive" pathway tracer 134Cs observed in earlier experiments where radiotracers were added to whole lakes or to larger enclosures.