Ti Isotopes Research Articles

NEW TITANIUM ISOTOPE DATA FOR ALLENDE AND EFREMOVKA CAIs

We measured the titanium (Ti) isotope composition, i.e., 50Ti/47Ti, 48Ti/47Ti, and 46Ti/47Ti, in five calcium-rich–aluminum-rich refractory inclusions (CAIs) from the oxidized CV3 chondrite Allende and in two CAIs from the reduced CV3 chondrite Efremovka. Our data indicate that CAIs are enriched in 50Ti/47Ti and 46Ti/47Ti and are slightly depleted in 48Ti/47Ti compared to normal Ti defined by ordinary chondrites, eucrites, ureilites, mesosiderites, Earth, Moon, and Mars. Some CAIs have an additional 50Ti excess of ∼8ε relative to bulk carbonaceous chondrites, which are enriched in 50Ti by ∼2ε relative to terrestrial values, leading to a total excess of ∼10ε. This additional 50Ti excess is correlated with nucleosynthetic anomalies found in 62Ni and 96Zr, all indicating an origin from a neutron-rich stellar source. Bulk carbonaceous chondrites show a similar trend, however, the extent of the anomalies is either less than or similar to the smallest anomalies seen in CAIs. Mass balance calculations suggest that bulk Allende Ti possibly consists of a mixture of at least two Ti components, anomalous Ti located in CAIs and a normal component possibly for matrix and chondrules. This argues for a heterogeneous distribution of Ti isotopes in the solar system. The finding that anomalous Ti is concentrated in CAIs suggests that CAIs formed in a specific region of the solar system and were, after their formation, not homogeneously redistributed within the solar system. Combining the CAI data with improved model predictions for early solar system irradiation effects indicates that a local production scenario for the relatively short lived radionuclides can be excluded, because the production of, e.g., 10Be, 26Al, and 41Ca, would result in a significant collateral shift in Ti isotopes, which is not seen in the measured data.

In Situ Ti Isotopic Measurements by Laser Ablation MC-ICP-MS

We have been developing Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) technique to measure titanium isotopic composition in situ. A principal aim of this work is to search for isotopic heterogeneities larger than the few epsilons (e, in parts in 10^4) of the solar system. Our analytical precision of the ratios of 46Ti, 48Ti, and 50Ti to 49Ti after exponential-law mass discrimination correction normalizing 47Ti/49Ti to 1.33375 were about 2.5 e(2δ). Mixture solutions were prepared by adding the expected level of Ca, Cr, Mg, and Al to the Ti solutions to demonstrate that our interference correction is effective. We then applied our technique with 213 nm Nd-YAG laser ablation to five Ti-rich terrestrial solids, and all of them also showed titanium isotopic composition that was consistent with one another and agreed with that for the solution standard. It appears that the in situ laser technique did not significantly increase the long-term reproducibility beyond the 2.5 e established using the solution method. This is an order of magnitude better than the typical precision of a few permil for secondary ion mass spectrometry (SIMS). The combination of the ability to perform in situ analysis on 30μm spots with e level precision is a niche for LA-MC-ICP-MS. We also ablated two lines on a fassaite grain from a large well studied CAI Egg-6 of the Allende meteorite. After the mass discrimination was corrected by normalizing 47Ti/49Ti, the 46Ti and 48Ti are normal within about 2 e while 50Ti/49Ti shows a 9 e excess. These data are in excellent agreement with thermal ionization mass spectrometry (TIMS) results. Comparing our ICP-MS results against the results from TIMS studies, we found that our normal titanium isotopic ratios were closest to the less precise data of Heydegger et al. (1979) who measured Ti(superscript +). We support the proposal to IUPAC to change the accepted Ti abundance to that measured by ICP-MS and TIMS without using Ti oxides.

Calculation and Analysis of the Complete Set of Neutron Data for 46,47,48,49,50,natTi in the Energy Region 0.3 to 20 MeV

The neutron-induced nuclear reactions of 46,47,48,49,50,natTi are calculated and analyzed for the CENDL library. First, one set of optimized optical model potential parameters for n + 46,47,48,49,50,natTi below 20 MeV is obtained. Based on these parameters, the complete neutron data are computed though the UNF and DWUCK4 codes for each of the Ti isotopes and the natural nuclide. All of the theoretical results are compared with the experimental data, together with the updated evaluations of other evaluation libraries. In addition, we verify the new results through the benchmark integral measurements from OKTAVIAN.

Single-neutron energies nearN=28and the absence of theN=34subshell closure in the Ti isotopes

The surprising absence of the $N=34$ subshell closure in the exotic nucleus $^{56}\mathrm{Ti}$ is highlighted by examining the experimental single neutron energies along the $N=28$ isotopes, which are extracted from previously existing data on single-neutron transfer reactions on stable isotones and nuclear masses. The results point out the role of the monopole effect of the tensor force on the ${f}_{7/2}\text{\ensuremath{-}}{f}_{5/2}$ splitting and confirm the prediction of the reduction of this splitting in the $Z>20$ isotones. In addition, the importance of making similar measurements of the distribution of single neutron and single neutron hole strength in the exotic $Z<20 N=28$ isotones is discussed. Measurements of the ($d,p$) reaction and the neutron knockout reaction on the exotic nucleus $^{46}\mathrm{Ar}$ have provided proof of principle for the necessary reactions, and advances presently taking place in detector technology will soon provide the tools necessary for reliably mapping the distribution of neutron strength in detail.

Possibility of production of neutron-rich isotopes in transfer-type reactions at intermediate energies

The production cross sections of neutron-rich isotopes of Mg, Al, Si, P, S, Cl, Ar, K, Ca, Sc, and Ti in the multinucleon transfer reactions 48 Ca(64 MeV/nucleon, 140 MeV/nucleon) + 181 Ta and 48 Ca(142 MeV/nucleon)+ nat W are estimated. A good agreement of the calculated results with the available experimental data confirms the mechanism of multinucleon transfer at almost peripheral collisions at intermediate energies. The global trend of production cross section with the charge (mass) number of target in reactions with 48 Ca beam is discussed for the future experiments.

New Stellar Sources for High‐Density, Presolar Graphite Grains

WepresentC,N,O,Si,Al-Mg,K,Ca,andTiisotopicanalyses ofsevenhigh-density(ORG1f, � � 2:02 2:04 gcm � 3 ) graphite grains from Orgueil with 12 C/ 13 C ratios smaller than 20. The presence of 44Ti in three of these grains indicates an origin in Type II supernovae (SNe). The 13 C excesses in these SNe grains, however, remain enigmatic. The remaining grains have extremely large Ca and Ti isotopic anomalies, some of which are much larger than those predicted for envelopes of asymptotic giant branch (AGB) stars. These anomalies in conjunction with low 12 C/ 13 C ratios can only be explained by pure nucleosynthetic He-shell components of AGB stars. Born-again AGB stars that experience a late He flash are able to explain the low 12 C/ 13 C ratios of some of the grains along with the presence of extreme enrichments in the Ca and Ti isotopes. This study indicates that high-density graphite grains havemultiple stellar sources: SNe and born-again AGB stars, in addition to the previously established low-metallicity AGB stars. Subject headingg dust, extinction — meteors, meteoroids — nuclear reactions, nucleosynthesis, abundances — stars: abundances — stars: AGB and post-AGB — supernovae: general

Deformation around Neutron-Rich Cr Isotopes in Axially Symmetric Skyrme-Hatree-Fock-Bogoliubov Method

We analyse the deformation mechanism in neutron-rich Cr, Fe and Ti isotopes with N = 32–44 using a Skyrme-Hartree-Fock-Bogoliubov mean-field code employing a twodimensional mesh representation in the cylindrical coordinate system. Evaluating the quadrupole deformation energy systematically, we show that the Skyrme parameter set SkM* gives a quadrupole instability around the neutron numbers N ∼ 38–42 in Cr isotopes, where the deformation energy curve suggests a transitional behavior with a shallow minimum extending to a large prolate deformation. The roles of a deformed N = 38 gap and the position of the neutron g 9 orbit are analysed in detail.

Disentangling Effects of Nuclear Structure in Heavy Element Formation

Forming the same heavy compound nucleus with different isotopes of the projectile and target elements allows nuclear structure effects in the entrance channel (resulting in static deformation) and in the dinuclear system to be disentangled. Using three isotopes of Ti and W, forming 232Cm, with measurement spanning the capture barrier energies, alignment of the heavy prolate deformed nucleus is shown to be the main reason for the broadening of the mass distribution of the quasifission fragments as the beam energy is reduced. The complex, consistently evolving mass-angle correlations that are observed carry more information than the integrated mass or angular distributions, and should severely test models of quasifission.

Study of photo-proton reactions driven by bremsstrahlung radiation of high-intensity laser generated electrons

Photo-nuclear reactions were investigated using a high power table-top laser. The laser system at the University of Jena (I ∼ 3–5×1019 W cm-2) produced hard bremsstrahlung photons (kT∼2.9 MeV) via a laser–gas interaction which served to induce (γ, p) and (γ, n) reactions in Mg, Ti, Zn and Mo isotopes. Several (γ, p) decay channels were identified using nuclear activation analysis to determine their integral reaction yields. As the laser-generated bremsstrahlung spectra stretches over the energy regime dominated by the giant dipole resonance (GDR), these yield measurements were used in conjunction with theoretical estimates of the resonance energies Eres and their widths Γres to derive the integral reaction cross-section σint(γ,p) for 25Mn, 48, 49Ti, 68Zn and 97, 98Mo isotopes for the first time. This study enabled the determination of the previously unknown cross-section ratios for these isotopes. The experiments were supported by extensive model calculations (Empire) and the results were compared to the Thomas–Reiche–Kuhn (TRK) dipole sum rule as well as to the experimental data in neighboring isotopes and good agreement was observed. The Coulomb barrier and the neutron excess strongly influence the ratios for increasing target proton and neutron numbers.

SHAPE PHASE TRANSITIONS AND POSSIBLE E(5) SYMMETRY NUCLEI FOR Ti ISOTOPES

Relativistic mean field theory is used to produce potential energy surfaces (PESs) for Ti isotopes. The relatively flat PESs suggest that 48, 52, 60 Ti , being on the way from vibrations to γ-unstable behavior, are the possible examples with the transitional dynamical symmetry E(5). Especially for 48 Ti , PES shows that it is a better candidate with E(5) symmetry. These conclusions are supported by the experimental data via the observed ratios of excitation energies.

TiF2: Linear or Bent?

Calling nonlinearity into question: When Ti atoms are isolated in fluorine-doped argon matrices, TiF4, TiF3, TiF2, and TiF are identified by their IR spectra. The Ti isotope pattern observed for the ν3 mode of TiF2 is indistinguishable from that of a linear geometry. Therefore, there is now no reliable evidence for the nonlinearity of any 3d transition-metal difluorides or dichlorides.

Atomic spectrometry update. Atomic mass spectrometry

The review this year is dominated by the large number of publications on AMS, ICP-MS and SIMS. The increasing number of new AMS installations bears witness to the increasing interest in the technique now that smaller and simpler systems are becoming more widely available. Although high-energy systems still have an important role to play, each of the new systems was compact and of relatively low-energy. The development of ion sources that can accept gaseous samples has lowered the sample size requirement for radiocarbon analysis such that it is now little more than the background level. Contamination therefore has become a major issue. The numerous papers on improvements to SIMS analysis demonstrate the important role the technique plays in materials science. Unlike for most of the techniques covered, fundamental studies on SIMS analysis abound with particular attention being paid to understanding the ionization processes and the representativeness of the measured ion beam. Quantum chemistry calculations have been used to determine the fundamental processes occurring in cell ICP-MS. This approach contrasted with the empirical studies that are normally undertaken. Although many applications are still being published using collision and/or reaction cell ICP-MS, there were fewer novel or fundamental studies than in previous years. This suggests that cell ICP-MS is becoming a more routine method of analysis. The same can probably also be said of hyphenated ICP-MS methods for speciation, which continues to grow in importance but which is very much at the applied end of the spectrum. Speciation is notable in that it cuts across a number of MS techniques and conventional organic MS techniques are increasingly being investigated for structure determination of organometallic species. Each year seems to find further expansion of MC-ICP-MS into ‘non-traditional’ isotope analysis. This was the year for Ti isotope analysis. This Update is the 21st and last annual review on atomic mass spectrometry and follows the same format as last year's.1 Although an attempt is made to consider all relevant refereed papers, conference abstracts, reports, book chapters and patents for inclusion, the content of the review is highly selective. The selection of papers is based on criteria applied to focus sharply on the most significant developments in instrumentation and methodology or improved understanding of the fundamental phenomena involved in the MS process. The main ruling criterion for all speciation papers is that the work should involve or be intended for the study of natural systems. For example, the study of synthetic metal clusters is generally not included whereas the determination of organometallic compounds in environmental samples is. Applications of atomic MS are not covered in this Update and readers are referred to the Updates on Industrial Analysis: Metals, Chemicals and Advanced Materials,2 Environmental Analysis3 and Clinical and Biological Materials, Food and Beverages.4 Other, fundamental, reviews appear on X-ray fluorescence spectrometry5 and atomic emission, absorption and fluorescence spectrometries.6 Throughout this review, the term molecular ion will be restricted to denote only the positive or negative radical ion formed by removal or capture, respectively, of an electron. In contrast, addition of a proton or cation to a neutral molecule gives molecular adduct ions. Deprotonated molecules are considered as fragments. Although reproducibility or precision is a key figure of merit in MS, there is no agreed format for quoting it. The reader can assume that values of precision given in this Update as a percentage correspond to the RSD unless otherwise specified. For isotope ratios, however, values of precision are generally given as the SD of a permil value. It is a widespread phenomenon that analytical techniques in general and MS in particular spawn a large number of abbreviations and acronyms. A glossary of all abbreviations used in this Update appears at the end of the review. Most abbreviations are not defined in the text but those which are unlikely to be commonly known are defined in the text when used first and again in the glossary. It should be noted that throughout the text the letter C denotes the element carbon and not the unit of charge, the coulomb.

Titanium isotopes and the radial heterogeneity of the solar system

The solar system is assumed to be uniform on a large scale in terms of the isotope composition of refractory elements. Here we show that the titanium (Ti) isotope compositions of carbonaceous chondrites differ from those of ordinary chondrites, eucrites, mesosiderites, ureilites, the Earth, Moon, and Mars, all of which are indistinguishable. Leachates and mineral separates demonstrate that this feature is homogeneously distributed within a range of phases in the carbonaceous chondrites Allende and Renazzo. The data therefore indicate that the solar nebula that fed planetesimals between ∼ 1 AU and ∼ 2.4 AU, e.g. Earth, Moon, Mars and the parent bodies of ordinary chondrites, eucrites, ureilites, and mesosiderites, was homogeneous for Ti (and Sr, Ba, Nd, Sm) isotopes. In contrast, carbonaceous chondrites, which probably formed beyond ∼ 2.7 AU appear to have acquired a distinct mix of primitive components, which is consistent with their lack of depletion in volatile elements and late formation.

One-particle excitations outside the 54Ti semi-magic core: The 55V and 55Ti yrast structures

The level structures of 55V and 55Ti, the two nuclei with a single nucleon outside the semi-magic 5422Ti32 core, have been investigated in order to provide new tests of full pf-shell calculations with the GXPF1A interaction. The addition of a proton does not appear to affect the N=32 shell gap significantly, although comparisons between calculations and experiment at high spins (Iπ⩾21/2−) indicate the need for a larger model space for an accurate description of the data in this regime. The energy separation between the νp1/2 and νf5/2 orbitals in neutron-rich Ti isotopes is not large enough to result in an N=34 shell gap. However, comparisons between the 55Ti data and the calculations argue for the presence of a sizable N=34 gap in 54Ca.

High precision titanium isotope measurements on geological samples by high resolution MC-ICPMS

A method has been developed for the precise and reproducible measurement of Ti isotopes in natural materials using high resolution MC-ICPMS. Instrumental mass fractionation is internally corrected using 49Ti/ 47Ti. Replicate measurements of synthetic standard solutions, terrestrial rocks, and the carbonaceous chondrite Allende yield a long-term reproducibility (2 σ) of 0.28 ɛ, 0.34 ɛ, and 0.28 ɛ for 50Ti/ 47Ti, 48Ti/ 47Ti, and 46Ti/ 47Ti, respectively. Isobaric interferences from 46,48Ca +, 50V +, 50Cr +, and doubly charged Zr can be corrected for reliably in separated Ti solutions with Ca/Ti < 5, V/Ti < 0.3, Cr/Ti < 0.2, and Zr/Ti < 1, respectively. Such elemental ratios are achieved easily in most samples using the anion-exchange procedure presented. Single and double charged polyatomic ions can either be resolved, e.g., 14N 36Ar +, or do not compromise the measurements. The method has been successfully applied to terrestrial rocks, meteorites, and various mineral separates. Terrestrial samples and standards agree within analytical uncertainties but are consistently different from the recommended values of Niederer et al. [F.R. Niederer, D.A. Papanastassiou, G.J. Wasserburg, Geochim. Cosmochim. Acta 45 (1981) 1017] with the largest effect on 50Ti/ 47Ti. The new results provide evidence that the recommended terrestrial 50Ti/ 47Ti is not well constrained; our data are higher by ∼13 ɛ than the recommended value. Better agreement is found with the values recommended by Heydegger et al. [H.R. Heydegger, J.J. Foster, W. Compston, Earth Planet. Sci. Lett. 58 (1982) 406]. Our best estimate for the isotopic composition of terrestrial Ti (relative to 49Ti/ 47Ti = 0.749766) is: 50Ti/ 47Ti = 0.73010, 48Ti/ 47Ti = 10.06884, and 46Ti/ 47Ti = 1.09325. This corresponds to an atomic weight of 47.877, significantly different from the value of 47.867 recommended by IUPAC. A 50Ti/ 47Ti anomaly for bulk Allende of 3.37 ± 0.51 ɛ is found, while for 48Ti/ 47Ti and 46Ti/ 47Ti the data are identical to the terrestrial value within the uncertainties. This is consistent with other recently reported differences between the bulk Earth and chondrites in neutron-rich nuclides.

Interference correction in analysis of stainless steel and multi-element determination by glow discharge quadrupole mass spectrometry

Multi-element determination in stainless steel has been carried out by glow discharge mass quadrupole spectrometry (GD-QMS). According to the influences on relative intensity of analytical elements and their stability, glow discharge parameters such as current, voltage and pre-burn time were investigated. Mass interferences of analytical elements were researched, as well as appropriate isotopes were selected for analysis. Correction formulas were established for interfered isotopes of Ti and Mo. Fifteen elements in solid samples of stainless steel were directly determined, and the method has satisfactory accuracy and precision.

Manganese–chromium isotope systematics of carbonaceous chondrites

In this article we present the results of Cr isotope investigations of different types of carbonaceous chondrites and of the pallasite Eagle Station. The 53Cr/ 52Cr ratios in the bulk samples of carbonaceous chondrites are correlated with 55Mn/ 52Cr ratios. The slope of the correlation line yields a 53Mn/ 55Mn ratio of (8.5 ± 1.5) × 10 − 6 at the time of Mn/Cr fractionation. Mapping this ratio onto an absolute time scale yields a time for this event of 4568.1 + 0.8/− 1.1 Ma ago. This time is very similar to the formation age of Efremovka CAIs of 4567.2 ± 0.6 Ma [Y. Amelin, A. N. Krot, I. D. Hutcheon, A. A. Ulyanov, Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions, Science 297 (2002) 1678–1683], to a time of the chondrule formation of 4568 ± 1 Ma ago [L.E. Nyquist, D. Lindstrom, D. Mittlefehldt, C.-Y. Shih, H. Wiesmann, S. Wentworth, R. Martinez, Manganese-chromium formation intervals for chondrules from the Bishunpur and Chainpur meteorites, Meteorit. Planet. Sci. 36 (2001) 911–938], which, most likely, constrains early global high-temperature Mn/Cr fractionation in a nebular setting. The bulk samples of carbonaceous chondrites exhibit clear 54Cr excesses ( 54Cr ⁎) that are correlated with the 53Cr excesses ( 53Cr ⁎) and also with Mn/Cr ratios. One possible explanation of this correlation is that 54Cr ⁎ is also radiogenic, like 53Cr ⁎, and was formed by the decay of the short-lived parent radionuclide 54Mn. The very short half-life of 54Mn of 312 days would require that both short-lived radionuclides 53Mn and 54Mn were generated locally in spallation reactions during the early period of an active sun. The alternative and possibly more plausible explanation is the heterogeneous addition of presolar material. The presolar component, enriched in 54Cr, is mostly contained in the matrix of carbonaceous chondrites. The relative amount of matrix decreases in the sequence CI > CM > CO,CV. A large proportion of Mn is associated with the matrix while Cr preferentially resides in the chondrules. Thus, the Mn/Cr ratio also follows the sequence CI > CM > CO > CV and is correlated with 54Cr. The acid-resistant residues of carbonaceous chondrites are characterized by relatively large excesses of 54Cr and moderate deficits of 53Cr. The magnitude of these excesses and deficits decreases in the sequence CI, CM, CV and may imply that Cr in the CM, and CV residues is increasingly more equilibrated with Cr from the rest of the meteorites. The 53Cr/ 52Cr and 54Cr/ 52Cr ratios in the residues are anti-correlated indicating that there are at least two Cr components of possibly presolar origin. All residues have large excesses of the most neutron-rich Ti isotope, 50Ti ⁎. The pattern of 50Ti ⁎ does not exactly follow that observed for 54Cr ⁎ but it is generally similar. The Cr isotope systematic of the pallasite Eagle Station indicates that the precursor of this meteorite was a CV-type material. The 53Mn– 53Cr system indicates that the Cr isotopes equilibrated in this meteorite 4557.5 ± 0.6 Ma ago.

μCR42β: Muon capture rates for double-beta decay

Gamma-rays following nuclear capture of negative muons in enriched 48Ti, 76Se, 106Cd, as well as natural Se and Cd targets were measured. Time evolution of several gamma-lines allowed to deduce the total μ-capture rates in Ti, Se and Cd isotopes, which are compared to the Primakoff estimate. The data on the partial μ-capture rates will be used for more precise calculation of the 2β-NMEs of 48Ca, 76Se and 106Cd.

Full fp-shell study of even-even 48-56Ti isotopes

The level schemes and transition rates {\em B}({\em E}2;$\uparrow$) of eve-even $^{48-56}$Ti isotopes were studied by performing large-scale shell model calculations with FPD6 and GXPF1 effective interactions. Excellent agreement were obtained by comparing the first 2$^{+}$ level for all isotopes with the recently available experimental data, but studying the transition strengths {\em B}({\em E}2; 0$^+_{g.s.} \to2^+_1$) for all Ti isotopes using constant proton-neutron effective charges prove the limitations of the present large-scale calculations to reproduce the experiment in detail.

Yrast structure of neutron-richTi53

{gamma} rays from neutron-rich Ti nuclei in the vicinity of N=32 have been studied at Gammasphere using deep-inelastic reactions induced by {sup 48}Ca beams on thick {sup 208}Pb and {sup 238}U targets. The {sup 53}Ti yrast cascade was identified for the first time, and the location in energy of states with spin up to I = 21/2 was determined. The excitations of {sup 53}Ti provide new tests of effective interactions for full-pf-shell calculations. Comparisons between theory and experiment for the highest spin states in {sup 53}Ti favor the recently proposed GXPF1A interaction, which accounts for the appearance of a neutron subshell closure at N=32 in Ti isotopes as well as for the lack of a similar subshell closure at N=34, as predicted by earlier calculations with another interaction.