Uranium series

The uranium smes offers other unique opportunities to date igneous rocks and sediments. Tite (1972) and Aitken (1974) discussed the procedure of dating by using members of the series. These radionuclides are in equilibrium in older rocks, and the amounts at equilibrium are proportional to their half-lives. The isotopes of interest to us are Th, Ra, and Pa. Dating of ocean sediments by means of the Th (ionium) method depends on die fact that Th is precipitated from seawater, while the uranium parent remains in solution. Conse-quendy, the concentration of in the sediment is no longer supplemented, and it decays at a half-life of 8 x Kf years. This implies that if Ae sediment has been deposited uniformly, the concentration of Th will decrease with increasing sediment depth and that the age of deposition can be estimated. 

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Lead, atomic number 82, is a member of Group 14 (IVA) of the Periodic Table. Ordinary lead is bluish grey and is a mixture of isotopes of mass number 204 (15%), 206 (23.6%), 207 (22.6%), and 208 (52.3%). The average atomic weight of lead from different origins may vary as much as 0.04 units. The stable isotopes are products of decay of three naturally radioactive elements (see Radioactivity, natural) comes from the uranium series (see Uraniumand... 

M. Gascoyne, in Uranium Series Disequilibrium Applications to Environmental Problems, ed. M. Ivanovich and R. S. Hannon, Clarendon Press, Oxford, 1982, pp. 32-55. 

Uranium Series 232 - Thorium Series 235 - Uranium Series ... 

M. Scott, in Uranium Series Disequilihria Applications to Environmental Problems, ed. M. 

Edwards RL, Gallup CD, Cheng H (2003) Uranium-series dating of marine and lacustrine carbonates. Rev Mineral Geochem 52 363-405... 

Attree RW, Cabell MJ, Cushing RL, Pieroni JJ (1962) A calorimetric determination of the half-life of thorium-230 and a consequent revision to its neutron capture cross section. Can J Phys 40 194-201 Bateman H (1910) Solution of a system of differential equations occurring in the theory of radioactive transformations. Proc Cambridge Phil Soc 15 423-427 Beattie PD (1993) The generation of uranium series disequilibria by partial melting of spinel peridotite ... 

Fame G (1986) Principles of Isotope Geology, Second Edition. John Wiley and Sons, New York Fleischer RL, Raabe OG (1975) Recoiling alpha-emitting nuclei. Mechanisms for uranium-series disequilibrium. Geochim Cosmochim Acta 42 973-978 Goldstein SJ, Murrell MT, Williams RW (1993) Pa and h chronology of mid-ocean ridge basalts. Earth Planet Sci Lett 115 151-159... 

Goldstein SJ, Stirling CH (2003) Techniques for measuring uranium-series nuchdes 1992-2002. Rev Mineral Geochem 52 23-57... 

Holden NE (1990) Total half-lives for selected nuclides. Pure Appl Chem 62(5) 941-958 Ivanovich M (1992) The phenomenon of radioactivity. In Uranium-series Disequilibrium Applications to Earth, Marine, and Environmental Sciences. Ivanovich M, Harmon RS (eds) Clarendon Press, Oxford, p 1-33... 

Ivanovich M, Harmon RS (1992) Uranium-series Disequilibrium Applications to Earth, Marine, and Environmental Sciences. Clarendon Press, Oxford... 

An additional material based on the extractant octyl-phenyl-N,N-diisobutyl-carbamoylmethylphosphine oxide, or CMPO, (marketed under the name TRU-Spec) has also been widely utilized for separations of transuranic actinides (Horwitz et al. 1993a) but is also useful for uranium-series separations (e.g., Burnett and Yeh 1995 Luo et al. 1997 Bourdon et al. 1999 Layne and Sims 2000). This material has even greater distribution coefficients for the uranium-series elements U (>1000), Th (>10000), and Pa. As shown in Figure 1, use of this material allows for sequential separations of Ra, Th, U, and Pa from a single aliquot on a single column. Separations of protactinium using this material (Bourdon et al. 1999) provide an alternative to liquid-liquid extractions documented in Pickett et al. (1994). 

Figure 1. Schematic diagram showing a TRU-spec extraction chromatography method for separation of uranium, thorium, protactinium, and radium from a single rock aliquot. Further purification for each element is normally necessary for mass spectrometric analysis. Analysis of a single aliquot reduces sample size requirements and facilitates evaluation of uranium-series dating concordance for volcanic rocks and carbonates. For TIMS work where ionization is negatively influenced by the presence of residual extractant, inert beads are used to help remove dissolved extractant from the eluant.

Instrumentation. Traditional methods of alpha and beta spectrometry instrumentation have changed little over the past decade. Alpha spectrometric methods typically rely on semi-conductor or lithium-drifted silicon detectors (Si(Li)), or more historically gridded ion chambers, and these detection systems are still widely used in various types of uranium-series nuclide measurement for health, environmental, and... 

Subsequently, a wide array of developments in TIMS methods for uranium-series measurement occurred during the past decade including initiation of methods for measurement of long-lived radium (Volpe et al. 1991 Cohen and O Nions 1991) and protactinium isotopes (Pickett et al. 1994 Bourdon et al. 1999), development of improved sources or ionization methods for TIMS analysis, and introduction of commercially available multi-collector TIMS instruments designed specifically for uranium and thorium isotopic measurement. 

Detection systems. Prior to the past decade, most instruments used for uranium-series analysis were single-collector instruments, for which ion beams of the various isotopes are cycled onto a single low-intensity detector, usually with electronics operating in pulse counting mode (Chen et al. 1986 Edwards et al. 1987 Bard et al. 1990 Goldstein et al. 1989 Volpe et al. 1991 Pickett et al. 1994), in order to measure the low-intensity ion beams of °Th, Pa, Pa, Ra and Ra. Daly detectors and... 

SIMS techniques have occupied somewhat of a narrower niche in uranium-series analysis, but have significantly improved Th isotope analysis relative to TIMS for chemically separated samples. The major improvement relative to TIMS is an improvement by about an order of magnitude in efficiency or sample size requirements for silicates. For uranium and/or thorium rich minerals such as carbonates and zircons, both SIMS and laser-ablation MC-ICPMS have been used for the direct in situ analysis of U and Th isotopes (Reid et al. 1997 Stirling et al. 2000) on very small (pg to ng levels of total U and Th) samples, at 10-100 pm scale resolution. 

Huang M, Hirabayashi A, Shirasaki T, Koiznmi H (2000) A multimicrospray nebulizer for microwave-induced plasma mass spectrometry. Anal Chem 72 2463-2467 Ivanovich M, Murray A (1992) Spectroscopic methods. In Uranium-Series Disequilibrium Applications to Earth, Marine, and Enviromnental Sciences, 2" Ed. Ivanovich M, Harmon RS (eds) Orfbrd Univ. Press, Oxford... 

Reagan MK, Volpe AM, Cashman KV (1992) and Th-series chronology of phonolite fractionation at Mount Erebus, Antartica. Geochim Cosmochim Acta 56 1401-1407 Reagan MK, Morris JD, Herrstrom EA, Murrell MT. (1994) Uranium series and beryllium isotope evidence for an extended history of subduction modification of the mantle below Nicaragua. Geochim Cosmochim Acta 58 4199-4212... 

Uranium-series Disequilibria in Mid-oeean Ridge Basalts Observations and Models of Basalt Genesis... 

Beattie P (1993a) The generation of uranium series disequilibria by partial melting of spinel peridotite constraints from partitioning studies. Earth Planet Sci Lett 117 379-391... 

Sturm ME, Goldstein SJ, Klein EM, Karson JA, Mnrrell MT (2000) Uranium-series age constraints on lavas from the axial valley of the Mid-Atlantic Ridge, MARK area. Earth Planet Sci Lett 181 61-70 Sun S, McDonongh WF (1989) Chemical and isotopic systematics of ocean basalts implications for mantle composition and processes. In Magmatism in the Ocean Basins. Saunders AD, Norry MJ (eds) Blackwell Scientific Pnbl. Oxford, p 313-345... 

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