Geological dating

This accurate measurement of the ratio of abundances of isotopes is used for geological dating, estimation of the ages of antiquities, testing athletes for the use of banned steroids, examining fine details of chemical reaction pathways, and so on. These uses are discussed in this book under various headings concerned with isotope ratio mass spectrometry (see Chapters 7, 14, 15, 16, 17, 47, and 48). 

In principle to all elements at low (ppb) concentrations. Valuable for first look analysis, at solid samples. Isotopic ratio measurements can distinguish between sources of elements in tracer studies and environmental samples. Use in geological dating based upon isotopic ratios. 

The ability to provide data on the isotopic composition of analyte elements, is a further special feature of the technique. This has already been exploited in a number of ways, including geological dating and the identification of sources of environmental lead contamination and poisoning. The radiogeneric source of lead means that different deposits may have different isotopic composition. In the UK this feature has been used to... 

Equation 11.118 finds practical application in cosmological studies and in geology (dating of sulfide deposits and sediments). Figure 11.27A shows, for instance, the Re-Os isochron for iron meteorites and the metallic phase of chondrites, obtained by Luck and Allegre (1983). The fact that all samples fit the same isochron within analytical uncertainty has three important cosmological implications ... 

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. 

Potassium has three naturally occurring isotopes 39K (93.08%), 40K (0.01%), and 41K (6.91%). The radioactive decay of 4,)K to argon (40Ar), half-life of 109 years, makes it a useful tool for geological dating. Some physical properties of potassium are summarized in Table 1 (1—3). 

Fleischer, R. L., and P. B. Price Techniques for geological dating of minerals by chemical etching of fission fragment tracks. Geochim. cosmochim. Acta 28, 1705 (1964). 

Geology Dating of geological samples - rocks and minerals Rb- Sr, Sm- Nd, 187Re 1870s, 238y 206p 3 ... 

Potassium forms 2.50% of earth s crust and was first isolated in 1807. It is one of the most reactive metals. Radioactive decay of to " °Ar is used as a tool in geological dating. 

Compston, W., Williams, I.S. Black, L.P. (1982) Use of the ion microprobe in geological dating. In BMR 82, Yearbook of Bureau of Mineral Resources, Geology and Geophysics. Canberra Australian Government Publishing Services, pp. 39-42. 

In nuclear equations for positron emission, the electron is written as either P" ", +ie, or je. Potassium-40, which is important in geologic dating, undergoes positron emission ... 

A radioactive nuclide with the symbol jgK is used for geologic dating. What is its atomic number and mass (nucleon) number Write two other ways to represent this nuclide. 

Students can use this tool to understand radioactive decay, nuclear decay chains, and geological dating via radioactive isotopes (such as the Mg-Al, K-Ar, Rb-Sr, and Pb-Pb systems). 

Thus from 3 mass spectrometrically determined isotope ratios (, tp Tm) known standard amount P = Pj + P2, the unknown number of atoms N2 in die sanqile is determined. The precision of this technique is largest when sample and standard are added in such proportions that IV P. Exanqiles of the use of this technique are givra in 5.8 on geologic dating. 

The half-life (ti/,) of carbon 14 is about 5,730 years, useful for objects younger than 50,000 years. Geological timescales are on the order of hundreds of millions to billions of years. Isotopes commonly employed for geologic dating include potassium 40 °Ar, ty, = 1.25 billion... 

TL) monitoring, personnel monitoring, geological dating, archaeological dating... 

Approximate axial g-tensors are frequently observed for transition metal ion complexes. Inorganic radicals can also have appreciable axial g-anisotropy. This property is of value for the assignment of ESR powder spectra in applied studies. Carbon dioxide radical anions, CO2, and related species contribute for instance to the ESR signal used for geological dating [21] see Chapter 9. The ESR spectrum of this anion has also been employed as an indicator that a certain foodstuff has been irradiated, for dosimetric purposes in certain carboxylic acid salts, and as a component in tooth enamel samples used in retrospective dosimetry. 

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