Isotope ratio measurements strontium isotopes

Rubidium-87 emits beta-particles and decomposes to strontium. The age of some rocks and minerals can be measured by the determination of the ratio of the mbidium isotope to the strontium isotope (see Radioisotopes). The technique has also been studied in dating human artifacts. Rubidium has also been used in photoelectric cells. Rubidium compounds act as catalysts in some organic reactions, although the use is mainly restricted to that of a cocatalyst. 

The measured strontium isotope ratios of modem guinea pigs from Ayacucho support the expected strontium isotope ratios based on the geologic... 

We start with another set of isotope signatures. The rate of erosion in the distant past can be estimated by measuring the ratio of strontium isotopes in marine carbonates. Two stable isotopes of strontium — strontium-86 and strontium-87 — differ in their distribution between the Earth s crust and the mantle underneath it. The mantle is rich in strontium-86, whereas the crust is more richly endowed with strontium-87. The major source of strontium-86 in the oceans is the igneous rock basalt. This rock is extruded continuously from the mantle at the mid-ocean ridges, from where it spreads slowly across the ocean floor before diving back into the mantle beneath the ocean trenches. A little strontium dissolves from the basalt into seawater. The speed of dissolution is more or less constant. The gradual build-up of dissolved strontium-86 in the oceans is balanced by a steady uptake of strontium by marine carbonates, such as limestone (calcium carbonate). This is because strontium can displace its sister element, calcium, in the crystalline structure of limestone. As each of these processes takes place at a steady rate, we would not expect the relative amount of strontium-86 in limestone to fluctuate a great deal. In fact it varies quite a lot. Strontium-87 is to blame. 

Platzner, I. T., Becker, J. S., and Dietze, H. J. 1999. Stability study of isotope ratio measurements for uranium and thorium by ICP-QMS. Atomic Spectroscopy 20(1), 6-12. Porter, C. R. and Kahn, B. 1964. Improved determination of strontium-90 in milk by an... 

The Prince Albert Mountains in the northern part of southern Victoria Land consist of a large number of nunataks located on the polar plateau at the heads of Mawson, Harbord, and David glaciers aU of which flow into the Ross Sea. Several of these nunataks are composed of siUs of Ferrar Dolerite although flows of Kirkpatrick Basalt occur on Brimstone Peak (75°48 S, 158°33 E). Molzahn et al. (1996) reported isotope ratios of strontium, neodymium, and osmium as well as trace-element concentrations of five dolerite samples from the nunataks of the Prince Albert Mountains and two basalt samples from Brimstone Peak, including rubidium, strontium, samarium, neodymium, rhenium (Re) and osmium (Os). They also measured isotope ratios of strontium, neodymium, and lead in clinopyroxene and plagioclase of these rocks. 

Inherent in all these methodologies, which measure either absolute Sr levels or strontium isotope ratios in mineralized tissue, is the assumption that diagenesis has not altered the signal since death. This has been a matter of some considerable debate (e.g., Nelson et al. 1986), but the consensus of current opinion amongst practitioners is that the repeated acid-washing procedures used remove any diagenetic mineral, because it has a higher... 

Despite the potential to track the spatial movement of marine shell beads, archaeometric attempts at sourcing have been minimal. We are aware of only three other groups that have taken this approach including a neutron activation analysis (NAA) of Busycon sp. shells and artifacts in the American Southeast (/), the use of strontium isotopes as a measure of geologic age of fossil shells in Southwest Europe (2), and the use of oxygen isotope ratios to source Sporufylus sp. beads in Central Europe (5). 

Sr). Over the past 30 years, lead and strontium isotope ratios have been measured with thermal ionization mass spectrometry (TIMS). Elemental salts are deposited on a filament heated to produce ionized particles, which are then sent into a mass spectrometer where they are detected by multiple Faraday cups arrayed such that ions of several masses are collected simultaneously. TIMS is capable of high precision isotope discrimination, but the instruments tend to be large and expensive, and extensive sample preparation is required prior to sample introduction. Newer ICP-MS-based technologies like multi-collector ICP-MS (especially laser ablation) circumvent some of the sample preparation issues while exploiting the precision of simultaneous mass discrimination, but they are still limited by the number and configuration of ion collectors. 

A similar set of experiments was performed to test our ability to precisely characterize strontium isotopes. For the archaeological chemistry of biological remains, strontium isotopes are useful for testing dietary hypotheses and for examining differences in place of birth and place of residence. To test the precision of strontium isotope ratio measurement using TOF-ICP-MS, we made glass fusion beads using NIST Strontium Carbonate Standard SRM 987 and... 

We tested this data acquisition method by first ablating bracketing concentration standard glasses that had been determined from previous measurements. All the samples in this analysis had total strontium elemental concentrations between 95 and 350 parts per million strontium. We then collected 150-300 one second ion count packets for MSr, Sr, 87 Sr and 88Sr, plus the instantaneous ratio of each isotope to Sr (Figure 3). 

G. Fortunato, K. Mumic, S. Wunderli, L. Pillonel, J. O. Bosset, G. Gremaud, Application of strontium isotope ratios measured by MC-ICP-MS for food authentication, J. Anal. Atom. Spectrom., 19 (2004), 227-234. 

Whereas the abundance of Sr in rubidium rich rocks changes over time due to the radioactive 3 decay of Rb as a function of the primordial rubidium concentration and the age of the mineral, the abundance of the stable Sr isotope and consequently the Sr/ Sr is constant in nature. The constant Sr/ Sr isotope ratio is often used for internal standardization (mass bias correction) during strontium isotope ratio measurements of Sr/ Sr. In the rubidium-strontium age dating method, the isotope ratios Sr/ Sr and Rb/ Sr are measured mass spectrometrically (mainly by TIMS or nowadays by ICP-MS) and the primordial strontium ratio ( Sr/ Sr)o at t = 0 and the age t of the rock can be derived from the isochrone (graph of measured Sr/ Sr isotope ratios (represented on the ordinate) as a function of the Rb/ Sr ratio (on the abscissa) in several minerals with different primordial Rb concentrations). The age of the minerals will be determined from the slope of the isochrone (e — 1), and the primordial isotope ratio ( Sr/ Sr)o from the point of intersection with the ordinate (see Figure 8.9). Rb-Sr age dating is today an... 

Strontium isotope ratios and abundances in samples from the oceanic crust may be used to determine the complete chemical mass balance of strontium exchange between seawater and basalt, including the loss of basaltic strontium to hydrothermal solutions, and uptake of basaltic or seawater strontium from hydrothermal solutions. A mass balance of this exchange can be made in four steps, (i) The relative amount of basaltic and seawater strontium in altered basalt can be determined from the measured Sr/ Sr of an altered sample as a (linear) mixture of strontium from the two end members, the (contemporaneous) seawater and basalt, (ii) The inventory of the basaltic and seawater strontium in an altered sample (in mg/kg) may then be determined from the above ratio of seawater and basalt in the sample and the total strontium abundance measured for this sample, (iii) Seawater strontium addition to the basalt is given directly by the seawater strontium inventory calculated in Step (ii). (iv) The determination of flux of basaltic strontium in or out of an altered sample is more complicated because it has to be related to the original inventory of strontium. It is determined as the difference between the original basaltic inventory and the basaltic strontium present in the altered sample. 

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