Boron isotope

Boron trifluoride is also employed in nuclear technology by uti1i2ing several nuclear characteristics of the boron atom. Of the two isotopes, B and B, only B has a significant absorption cross section for thermal neutrons. It is used in " BF as a neutron-absorbing medium in proportional neutron counters and for controlling nuclear reactors (qv). Some of the complexes of trifluoroborane have been used for the separation of the boron isotopes and the enrichment of B as (84). 

Examination of possible systems for boron isotope separation resulted in the selection of the multistage exchange-distillation of boron trifluoride—dimethyl ether complex, BF3 -0(CH3 )2, as a method for B production (21,22). Isotope fractionation in this process is achieved by the distillation of the complex at reduced pressure, ie, 20 kPa (150 torr), in a tapered cascade of multiplate columns. Although the process involves reflux by evaporation and condensation, the isotope separation is a result of exchange between the Hquid and gaseous phases. 

A. A. Palko, The Chemical S eparation of Boron Isotopes, ORNE-5418, Oak Ridge National Laboratory, Oak Ridge, Term., June 1978. 

Boron [7440-42-8] B, is unique in that it is the only nonmetal in Group 13 (IIIA) of the Periodic Table. Boron, at wt 10.81, at no. 5, has more similarity to carbon and siUcon than to the other elements in Group 13. There are two stable boron isotopes, B and B, which are naturally present at 19.10—20.31% and 79.69—80.90%, respectively. The range of the isotopic abundancies reflects a variabiUty in naturally occurring deposits such as high B ore from Turkey and low °B ore from California. Other boron isotopes, B, B, and B, have half-Hves of less than a second. The B isotope has a very high cross-section for absorption of thermal neutrons, 3.835 x 10 (3835 bams). This neutron absorption produces alpha particles. 

Ishikawa, T. and Nakamura, E. (1993) Boron isotope systematics of marine sediments. Earth Planet. Sci. Lett., 117, 567-580. 

Spivack AJ, Edmond JM (1987) Boron isotope exchange between seawater and the oceanic crust. Geochim Cosmochim Acta 51 1033-1043... 

A. Deyhle. Improvements of Boron Isotope Analysis by Positive Thermal Ionization Mass Spectrometry Using Static Multicollection of CS2BO2 Ions. Int. J. Mass Spectrom., 206(2001) 79-89. 

Kakihana H, Kotaka M, Satoh S, Nomura M, Okamoto M (1977) Fundamental studies on the ion-exchange separation of boron isotopes. Bull Chem Soc Japan 50 158-163 Kieffer SW (1982) Thermodynamics and lattice vibrations of minerals 5. Applications to phase equilibria, isotopic fractionation, and high-pressure thermodynamic properties. Rev Geophys Space Phys 20 827-... 

O Neil JR (1986) Theoretical and experimental aspects of isotopic fractionation. Rev Mineral 16 1-40 Oi T (2000) Calculations of reduced partition function ratios of monomeric and dimeric boric acids and borates by the ab initio molecular orbital theory. J Nuclear Sci Tech 37 166-172 Oi T, Nomura M, Musashi M, Ossaka T, Okamoto M, Kakihana H (1989) Boron isotopic composition of some boron minerals. Geochim Cosmochim Acta 53 3189-3195 Oi T, Yanase S (2001) Calculations of reduced partition function ratios of hydrated monoborate anion by the ab initio molecular orbital theory. J Nuclear Sci Tech 38 429-432 Paneth P (2003) Chlorine kinetic isotope effects on enzymatic dehalogenations. Accounts Chem Res 36 120-126... 

Sahoo SK, Masuda A (1995) Simultaneous measurement of lithium and boron isotopes as lithium tetraborate ion by thermal ionization mass-spedrometry. Analyst 120 335-339... 

SpivackAJ, Edmond JM (1986) Determination of boron isotope ratios by thermal ionization mass spectrometry of the dicesium metaborate cation. Anal Chem 58 31-35 Spivack AJ, Kastner M, Ransom B (2002) Elemental and isotopic chloride geochemistry and fluid flow in the Nankai Trough. Geophys Res Lett 29 1-4... 

Nakane ei al. (1964) established equilibrium constants of boron isotope exchange between boron trifluoride gas on one side and boron trifluoride methyl fluoride, methyl chloride, isopropyl chloride and t-butyl chloride. The value of the equilibrium constants, which represents the thermodynamic isotope effect, was related to the polarity, stability and catalytic activity of the complexes. 

Fig. 2.7 Boron isotope variations in some geologically important reservoirs...

As analytical techniques have been consistently improved in recent years, the number of boron isotope studies has increased rapidly. Reviews have been given by Barth (1993) and by Palmer and Swihart (1996). The total boron isotope variation documented to date is about 90%c. 5 B-values are generally given relative NBS boric acid SRM 951, which is prepared from a Searles Lake borax. This standard has a B/ °B ratio of 4.04558 (Palmer and Slack 1989). 

This approach has been not only used to directly estimate the ocean pH from 8 B of foraminifera but to estimate from the pn the past atmospheric CO2 concentrations (i.e. Pearson and Palmer 1999,2000 Pagani et al. 2005). An increase in atmospheric CO2 results in increased dissolved CO2 in ocean water, which in turn causes a reduction in oceanic pn- A note of caution was presented by Lemarchand et al. (2000) who suggested that boron isotope variations in foraminifera depend at least in part on variations in the supply of riverine boron to the ocean during the geologic past. And indeed the boron isotope composition of rivers can be extremely variable (Rose et al. 2000 Lemarchand et al. 2002). Joachimski et al. (2005) presented evidence... 

Since hthium and boron isotope fractionations mainly occur during low temperature processes, Li and B isotopes may provide a robust tracer of surface material that is recycled to the mantle (Elhott et al. 2004). Heterogeneous distribution of subducted oceanic and continental crust in the mantle will thus result in variations in Li and B isotope ratios. Furthermore, dehydration processes active in subducdon zones appear to be of crucial importance in the control of Li and B isotope composition of different parts of the mantle. For the upper mantle as a whole Jeffcoate et al. (2007) gave an estimated 8 Li-value of 3.5%o. 

Since boron concentrations in mantle minerals are exceedingly low, boron isotope analysis of mantle minerals are very restricted. On the basis of a boron budget between mantle and crust, Chaussidon and Marty (1995) conclnded that the primitive mantle had a 5 B-value of-10 2%c.ForMORB Spivack and Edmond (1987) and Chaussidon and Marty (1995) reported a 5 B-value of aronnd -4%c. Higher and lower 5 B-values observed in some ocean island basalts shonld be due to crustal assimilation (Tanaka and Nakamura 2005). 

The boron isotope approach to pC02 estimation relies on the fact that a rise in the atmospheric CO2 concentration will increase pC02 of the surface ocean which in turn causes a reduction of its pH. By measuring the boron isotope composition of planktonic foraminifera Pahner et al. (1998) and Pearson and Palmer (2000) have reconstructed the pH-profile of Eocene sea water and estimated past atmospheric CO2 concentrations. However, Lemarchand et al. (2000) argued that 5 B records of planktonic foraminifera partly reflect changes in the marine boron isotope budget rather than changes in ocean pH. 

Baroni M, Thiemens MH, Delmas RJ, Savarino J (2007) Mass-independent sulfur isotopic composition in stratospheric volcanic eruptions. Science 315 84-87 Barth S (1993) Boron isotope variations in nature a synthesis. Geologische Rundschau 82 640-651... 

Hemming NG, Hanson GN (1992) Boron isotopic composition in modern marine carbonates. Geochim Cosmochim Acta 56 537-543... 

Jiang SY, Palmer MR (1998) Boron isotope systematics of tourmaline from granites and tourmalines a synthesis, Eur J Miner 10 1253-1265... 

Klochko K, Kaufman AJ, Yao W, Byrne RH, Tossell JA (2006) Experimental measurement of boron isotope fractionation in seawater. Earth Planet Sci Lett 248 276-285 Kloppmann Girard NSgrel P (2002) Exotic stable isotope composition of saline waters and brines from the crystalline basement. Chem Geol 184 49-70 Knauth LP (1988) Origin and mixing history of brines, Palo Duro Basin, Texas, USA, Applied Geochemistry 3 455 74... 

Liebscher A, Meixner A, Romer R, Heinrich W (2005) Liquid-vapor fractionation of boron and boron isotopes experimental calibration at 400°C/23 Mpa to 450°C/42Mpa. Geochim Cosmochim Acta 69 5693-5704... 

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