Rubidium abundance

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. 

The element is much more abundant than was thought several years ago. It is now considered to be the 16th most abundant element in the earth s crust. Rubidium occurs in pollucite, leucite, and zinnwaldite, which contains traces up to 1%, in the form of the oxide. It is found in lepidolite to the extent of about 1.5%, and is recovered commercially from this source. Potassium minerals, such as those found at Searles Lake, California, and potassium chloride recovered from the brines in Michigan also contain the element and are commercial sources. It is also found along with cesium in the extensive deposits of pollucite at Bernic Lake, Manitoba. 

Rubidium [7440-17-7] Rb, is an alkali metal, ie, ia Group 1 (lA) of the Periodic Table. Its chemical and physical properties generally He between those of potassium (qv) and cesium (see Cesiumand cesium compounds Potassium compounds). Rubidium is the sixteenth most prevalent element ia the earth s cmst (1). Despite its abundance, it is usually widely dispersed and not found as a principal constituent ia any mineral. Rather it is usually associated with cesium. Most mbidium is obtained from lepidoHte [1317-64-2] an ore containing 2—4% mbidium oxide [18088-11-4]. LepidoHte is found ia Zimbabwe and at Bernic Lake, Canada. 

Rubidium (78 ppm, similar to Ni, Cu, Zn) and caesium (2.6 ppm, similar to Br, Hf, U) are much less abundant than Na and K and have only recently become available in quantity. No purely Rb-containing mineral is known and much of the commercially available material is obtained as a byproduct of lepidolite processing for Li. Caesium occurs as the hydrated aluminosilicate pollucite, Cs4ALiSi9026.H20, but the world s only commercial source is at Bemic Lake,... 

Zinc (76ppm of the earth s crust) is about as abundant as rubidium (78 ppm) and slightly more abundant than copper (68 ppm). Cadmium (0.16 ppm) is similar to antimony (0.2 ppm) it is twice as abundant as mercury (0.08 ppm), which is itself as abundant as silver (0.08 ppm) and close to selenium (0.05 ppm). These elements are chalcophiles (p. 648) and so, in the reducing atmosphere prevailing when the earth s crust solidified, they separated out in the sulfide phase, and their most important ores are therefore sulfides. Subsequently, as rocks were weathered, zinc was leached out to be precipitated as carbonate, silicate or phosphate. 

Rubidium has two naturally occurring isotopes 8SRb (atomic mass = 84.9118 amu) and 87Rb (atomic mass = 86.9092 amu). The percent abundance of 87Rb can be estimated to be which of die following ... 

In the other study. X-ray fluorescence spectroscopy was used to analyze trace element concentrations by observing dusts on 37 ram diameter cellulose acetate filters (20). Twenty-three elutriator and twenty-three area samples from 10 different bales of cotton were analyzed. The average fraction of total dust accounted for by the elements analyzed was 14.4% amd 7.6% for vertical elutriator and area samples, respectively. Although the variation in absolute quantity of atn element was high, the relative abundance of an element was consistent for measurements within a bale. Averaged over all the samples analyzed, calcium was the most abundant element detected (3.6%), followed by silicon (2.9%), potassium (2.7%), iron (1.1%), aluminum (1.1%), sulfur (1.0%), chlorine (0.8%) and phosphorous (0.6%). Other elements detected in smaller aunounts included titanium, manganese, nickel, copper, zinc, bromine, rubidium, strontium, barium, mercury amd lead. 

Rubidium does not exist in its elemental metallic form in nature. However, in compound forms it is the 22nd most abundant element on Earth and, widespread over most land areas in mineral forms, is found in 310 ppm. Seawater contains only about 0.2 ppm of rubidium, which is a similar concentration to lithium. Rubidium is found in complex minerals and until recently was thought to be a rare metal. Rubidium is usually found combined with other Earth metals in several ores. The lepidolite (an ore of potassium-lithium-aluminum, with traces of rubidium) is treated with hydrochloric acid (HCl) at a high temperature, resulting in lithium chloride that is removed, leaving a residue containing about 25% rubidium. Another process uses thermochemical reductions of lithium and cesium ores that contain small amounts of rubidium chloride and then separate the metals by fractional distillation. 

Rubidium is widely distributed in nature. Its abundance in the earth s crust is estimated to be 90 mg/kg. Rubidium occurs at trace levels in many potassium minerals. Often it is associated with cesium. Some rubidium-con-... 

A popular method used to date rocks is the potassium-argon method. Potassium is abundant in rocks such as feldspars, hornblendes, and micas. The K-Ar method has been used to date the Earth and its geologic formations. It has also been applied to determine magnetic reversals that have taken place throughout the Earth s history. Another method used in geologic dating is the rubidium-strontium, Rb-Sr, method. Some of the oldest rocks on Earth have been dated with this method, providing evidence that the Earth is approximately 5 billion years old. The method has also been used to date moon rocks and meteorites. 

The abundances of krypton and xenon are determined exclusively from nucleosynthesis theory. They can be interpolated from the abundances of neighboring elements based on the observation that abundances of odd-mass-number nuclides vary smoothly with increasing mass numbers (Suess and Urey, 1956). The regular behavior of the s-process also provides a constraint (see Chapter 3). In a mature -process, the relative abundances of the stable nuclides are governed by the inverse of their neutron-capture cross-sections. Isotopes with large cross-sections have low abundance because they are easily destroyed, while the abundances of those with small cross-sections build up. Thus, one can estimate the abundances of krypton and xenon from the abundances of. v-only isotopes of neighboring elements (selenium, bromine, rubidium and strontium for krypton tellurium, iodine, cesium, and barium for xenon). 

There are two basic ways to apply the 87Rb-87Sr technique to natural samples. The original method is to simply measure the isotopic composition of strontium and the abundance of rubidium in a rock and then calculate a date. If the rock contains no common strontium, a date can be calculated from ... 

In the rubidium-strontium age dating method, radioactive 87Rb isotope with a natural isotope abundance of 27.85 % and a half-life of 4.8 x 1010 a is fundamental to the 3 decay to the isobar 87 Sr. The equation for the Rb-Sr method can be derived from Equation (8.9) ... 

Whereas the abundance of 87 Sr in rubidium rich rocks changes over time due to the radioactive 3... 

Table 1-4 compares the composition of a bacterium, of a green plant, and of an active animal tissue (rat liver). Although the solid matter of cells consists principally of C, H, O, N, S, and P, many other chemical elements are also present. Among the cations, Na+, K+, Ca2+, and Mg2+ are found in relatively large amounts. Tlius, the body of a 70 kg person contains 1050 g Ca (mostly in the bones), 245 g K, 105 g Na, and 35 g Mg. Iron (3 g), zinc (2.3 g), and rubidium (1.2 g) are the next most abundant. Of these iron and zinc are essential to life but rubidium is probably not. It is evidently taken up by the body together with potassium. 

K is a (3 -emitting nuclide that is the predominant radioactive component of normal foods and human tissue. Due to the 1460-keV 7 ray that accompanies the (3 decay, it is also an important source of background radiation detected by 7-ray spectrometers. The natural concentration in the body contributes about 17 mrem/y to the whole body dose. The specific activity of 40K is approximately 855 pCi/g potassium. Despite the high specific activity of 87Rb of 2400 pCi/g, the low abundance of rubidium in nature makes its contribution to the overall radioactivity of the environment small. 

Nier, A. O. (1950b) A redetermination of the relative abundances of the isotopes of neon, krypton, rubidium, xenon and mercury. Phys. Rev., 19, 450-4. 

Rubidium ignites spontaneously when exposed to oxygen to form rubidium oxide, RbaO. Rubidium exists as two isotopes fRb (84.91 u) and (jyRb (86.91 u). If the average atomic mass of rubidium is 85.47 u, determine the percentage abundance of Rb. 

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... 

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... 

Limitations, (i) As with other radionuclide-based ages, the terrestrial age of the sample must be known, (ii) Concentrations of Kr are quite low in most meteorites, typically just 5 X 10 atomg in chondrites. For this reason, Kr measurements are still scarce and their uncertainties can be relatively large, often —20%. (iii) Production rates for krypton isotopes may vary with the abundances of rubidium, yttrium, and zirconium relative to strontium. It should be understood that the original basis for the calculation of Pgi/Fgs was a set of relative cross-section measurements for the production of krypton from silver (Marti, 1967). 

Abundances of nonrefractory incompatible lithophile elements (potassium, rubidium, caesium, etc.) or partly siderophile/chalcophile elements (tungsten, antimony, tin, etc.) are calculated from correlations with RLE of similar compatibility. This approach was first used by Wanke et al. (1973) to estimate abundances of volatile and siderophile elements such as potassium or tungsten in the moon. The potassium abundance was used to calculate the depletion of volatile elements in the bulk moon, whereas the conditions of core formation and the size of the lunar core may be estimated from the tungsten abundance, as described by Rammensee and Wanke (1977). This powerful method has been subsequently applied to Earth, Mars, Vesta, and the parent body of HED meteorites. The procedure is, however, only applicable if an incompatible refractory element and a volatile or siderophile element have the same degree of incompatibility, i.e., do not fractionate from each other during igneous processes. In other words, a good correlation of the two elements over a wide... 

---