Rubidium isotope ratio measurements

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... 

Moens and co-workers used the fluoride transfer reaction frommethyl fluoride to Sr+ (resulting in the formation of SrF+) to separate the strontium isotope pattern from a rubidium-containing background matrix, with the aim of making Rb-interference free isotope ratio measurements of strontium. However, it has been proposed that mass discrimination effects due to the ion-molecule reaction can alter the experimentally determined isotope pattern, thereby degrading the accuracy of isotope ratio measurements made using this approach. Consider the reaction... 

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 rubidium 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 oiganic reactions, although the use is mainly restricted to that of a cocatalyst. 

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. 

Rubidium abundances in cool giants are measureable from the Rbl 7800A line. Unfortunately, the Rb isotopic mix is not measureable because the hyperfine structure from 85Rb and 87Rb adds confusion. Our analyses of the 7800A line in a sample of M, MS, and S giants showed Rb to increase with the s-process enrichment of the atmosphere. The Rb/Sr ratio suggested a low neutron density around 107 cm-3. 

Information concerning the origin of the alkali-rich lavas of the Erebus volcanic province is derivable from the isotopic composition of strontium and the concentrations of rubidium and strontium. The first measurements of the Sr/ Sr ratios of the Cenozoic volcanic rocks in the Erebus province by Jones and Walker (1972) ranged from 0.7022 to 0.7048 with a mean of 0.70365 0.0024 (2o). These measurements demonstrated that the Cenozoic lavas are only moderately enriched in radiogenic Sr in marked contrast to the basalt flows and dolerite sills of the Eerrar Group. These results were later confirmed by Stuckless and Ericksen (1976) whose measured Sr/ Sr ratios in Figs. 16.6a, b, and c have a nnimodal distribution with a mean of 0.70332 0.00005 (2. ... 

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