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2
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0001496063
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A. S. Cohen, R. K. O'Nions, R. Siegenthaler, W. I. Griffin, Contrib. Mineral. Petrol. 98, 303 (1988).
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Cohen, A.S.1
O'Nions, R.K.2
Siegenthaler, R.3
Griffin, W.I.4
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4
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0028828016
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K. Burton, M. J. Kohn, A. S. Cohen, R. K. O'Nions, ibid. 133, 199 (1992).
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Earth Planet. Sci. Lett.
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Burton, K.1
Kohn, M.J.2
Cohen, A.S.3
O'Nions, R.K.4
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8
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3542997137
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note
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149Sm concentrations varying between ∼100 and 200 ppm in two different stock solutions used in this work.
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10
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3543037852
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note
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- accelerated to 10 keV. The samples were held at ∼+4.5 kV, resulting in an impact energy of ∼14.5 keV. Two approaches were used to avoid contribution of secondary ions from the crater walls. For some of the samples, a 50-nA primary beam was focused onto a spot and rastered over a 200 μm by 200 μm area. An aperture inserted into the path of the ions allowed only those originating from a 60-μm-diameter circular area in the center of the crater into the mass spectrometer. For other samples, a 15-to 20-nA primary beam was focused by Kohler illumination to generate a circular, flat-bottomed crater ∼120 μm in diameter (24). Secondary ions from the central 10 or 20 μm of the crater were allowed into the mass spectrometer by selecting either a 100-or 200-μm field aperture. In both cases a 75-V offset was applied to the sample voltage to minimize the contribution of molecular ions to the mass spectrum (25). Crater depths were determined with a Dektak surface profilometer and varied as a function of primary beam current and analysis time (1 to 2 hours) between ∼3000 and 7000 Å.
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15
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0001063588
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Diffusion, Atomic Ordering and Mass Transport, J. Ganguly, Ed. Springer-Verlag, New York
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S. Chakraborty and J. Ganguly, in Diffusion, Atomic Ordering and Mass Transport, J. Ganguly, Ed. (Advances in Physical Geochemistry 8, Springer-Verlag, New York, 1991), pp. 120-175.
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Advances in Physical Geochemistry
, vol.8
, pp. 120-175
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Chakraborty, S.1
Ganguly, J.2
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16
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3543015246
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M. Morioka H. Nagasawa, in (15), pp. 176-197
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M. Morioka and H. Nagasawa, in (15), pp. 176-197.
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19
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3543014622
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thesis, Brown University, Providence, RI
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R. A. N. Coghlan, thesis, Brown University, Providence, RI (1990).
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(1990)
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Coghlan, R.A.N.1
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22
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3543036680
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_, Mat. Sci. Forum 7, 145 (1986).
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(1986)
Mat. Sci. Forum
, vol.7
, pp. 145
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23
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3543009862
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in preparation
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C in Dodson's (21) eqn. 23 equals exp(G), where G is the spatially averaged value of the closure function G(X) of his (22) eqn. 20. In deriving the expression for G(X), Dodson (22) assumed that the dimensionless quantity M ≫ 1, which implies removal of the composition of the crystal from its initial composition in all parts. The closure function has been modified so that it is valid for any arbitrary value of M, numerically evaluated as a function of the normalized radial distance from the center of a grain, and then spatially averaged to yield average closure function versus M; for example, G(M = 0.001) = 0.9018, G(0.01) = 2.7603, G(0.10) = 3.8693, G(0.4) = 4.0041, as compared to Dodson's (22) G = 4.0066.
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Ganguly, J.1
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24
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3543025394
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A. Bennighoven, Ed. Wiley, Munster, Germany
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S. W. J. Clement, W. Compston, C. Newstead, in Proceedings International Secondary Ion Mass Spectrometry Conference, A. Bennighoven, Ed. (Wiley, Munster, Germany, 1991), pp. 289-293.
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(1991)
Proceedings International Secondary Ion Mass Spectrometry Conference
, pp. 289-293
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Clement, S.W.J.1
Compston, W.2
Newstead, C.3
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26
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3543004389
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note
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We thank M. H. Dodson and J. Ruiz for helpful discussions and for providing some of the isotopeenriched solutions, respectively. This research was supported by U.S. National Science Foundation grant EAR 9418941 and EAR 9805232.
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