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Periodic Table--Silver

107Pd decays by emission to 107Ag with a half-life of 6.5 Myr. Iron meteorites are the only objects with a high enough Pd/Ag ratio to yield measurable variations in 107Ag abundance. Radiogenic 107Ag was first discovered in the Santa Clara meteorite by Kelly and Wasserburg (1978). They suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 Myr after a nucleosynthetic event. 107Pd versus Ag correlations observed in bodies, which have clearly been melted since accretion of the solar system, must reflect the presence of live short-lived nuclides in the early solar system (Chen and Wasserburg, 1984, 1990).

Similarities observed between the initial iodine, aluminum and palladium ratios in meteorites indicate that if the additions of hot material occurred early in the formation of the solar-system, then their different half-lives would have attenuated the short-lived nuclides to very different degrees by the time of condensation (Wasserburg and Papanastassiou, 1982).

Source of text: This review was assembled by Eric Caldwell, primarily from Dicken (1995).

Chen, J.H. and Wasserburg, G.J. (1984). "The origin of excess 107Ag in Gibeon (IVA) and other iron meteorites." In: Lunar Planet. Sci. XV, Lunar Planet. Inst., 144 (abstract).
Chen, J.H. and Wasserburg, G.J. (1990). "The isotopic composition of Ag in meteorites and the presence of 107Pd in proto-planets." Geochim. et Cosmochim. Acta, 54: 1729-1743.
Clayton, D.D. (1975). "Extinct radioactivities: trapped residuals of presolar grains." Astrophys. J., 199: 765-769.
Dicken, A.P. (1995). Radiogenic Isotope Geology. Cambridge University Press, New York, 452 pp.
Kelly, W.R. and Wasserburg, G.J. (1978). "Evidence for the existence of 107Pd in the early solar-system." Geophys. Res. Lett., 5: 1079-1082.
Wasserburg, G.J. (1985). "Short-lived nuclei in the early solar-system." In: D.C. Black and M.S. Matthews (Eds.), Protostars and Planets. Univ. Arizona Press, pp. 703-737.
Wasserburg, G.J. and Papanastassiou, D.A. (1982). "Some short-lived nuclides in the early solar-system - a connection with the placental ISM." In: C.A. Barnes, D.D. Clayton and D.N. Schramm (Eds.), Essays in Nuclear Astrophysics. Cambridge University Press, pp. 77-140.
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