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Evidence for the existence of ^(107)Pd in the early solar system

Kelly, William R. and Wasserburg, G. J. (1978) Evidence for the existence of ^(107)Pd in the early solar system. Geophysical Research Letters, 5 (12). pp. 1079-1082. ISSN 0094-8276. doi:10.1029/GL005i012p01079.

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The concentration and isotopic composition of Ag and Pd were measured in the Santa Clara iron meteorite. This meteorite has Pd/Ag of about 10^4. The isotopic composition of Pd is identical to terrestrial Pd within 0.1%. The ^(107)Ag/^(109)Ag ratio was 4% greater than the terrestrial value and suggests the in situ decay of ^(107)Pd(τ_½ = 6.5 × 10^6y) in this meteorite or its parent body. From the observed ^(107)Ag^*/^(110)Pd ratio (^* ≡ excess) we infer an initial (^(107)Pd/^(110)Pd)_⊙ ⩾2 × 10^(−5). These data are incompatible with an interval of ∼ 10^8y between the end of nucleosynthesis and the formation of planetary objects but are compatible with a last-minute injection of material. The inferred existence of ^(107)Pd and ^(26)Al indicates that the late injection included freshly synthesized material of both intermediate and low atomic weight on a similar time scale. We estimate the fraction of freshly synthesized material to be between 10^(−5) to 10^(−4) in the region of Z ∼ 50. The ^(244)Pu and some of the ^(129)I present in the early solar system may be due to earlier contributions. The highly granular nature of stellar nucleosynthesis is made apparent by these considerations. The ^(107)Pd-^(107)Ag chronometer is of particular importance as it can measure the time interval between the last injection of freshly synthesized material and the formation of differentiated planetary-size objects. Our data suggest that the time scale for the differentiation of some planets into large scale metallic and silicate segregations is as short as ∼10^6y.

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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1978 American Geophysical Union. Article fist published online 7 Dec 2012. Received October 26, 1978; accepted November 14, 1978. It is our hope that we have not confused a baser substance with the true silver image of the goddess-asteroid Pallas. We wish to express our indebtedness to previous workers who thought of and sought for evidence of this extinct nuclide over the past 30 years. This study could not have been accomplished without collaboration with Fouad Tera in the initial stages of this work. His continued telephonic interest in the problem was helpful and stimulating. The senior author acknowledges Fouad Tera's magian powers and his demonstration that a camel can go through the eye of a micro-ion exchange column. Samples of Santa Clara were obtained through the courteous cooperation of C. B. Moore and C. F. Lewis of the Center for Meteorite Studies, Arizona State University. The early encouragement and support of J. W. Larimer is appreciated. The authors thank D. A, Papanastassiou for his incisive collegial commentary. This work was supported by NSF 76-83685 and NASA NGL 05-002-188. Contribution 3166 (282).
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NASANGL 05-002-188
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Caltech Division of Geological and Planetary Sciences 3166
Lunatic Asylum Lab282
Issue or Number:12
Record Number:CaltechAUTHORS:20131217-083240256
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Official Citation:(1978), Evidence for the existence of 107Pd in the early solar system. Geophysical Research Letters, 5: 1079–1082. doi: 10.1029/GL005i012p01079
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43037
Deposited By: Ruth Sustaita
Deposited On:17 Dec 2013 16:49
Last Modified:10 Nov 2021 16:32

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