Trapped Xe and I-Xe ages in aqueously altered CV3 meteorites

Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016), 2017

The preserved record of decay of now-extinct 129 I into 129 Xe forms the basis of the I-Xe chronometer. Comparison of the high precision I-Xe and Pb-Pb ages of chondrules and pure mineral phases separated from eight meteorites suggests the 17.5 ÷ 14.6 Ma range for the 129 I half-life, assuming that the 235 U and 238 U half-lives are correct. The mean value of 16 Ma indicates that the 15.7 Ma half-life of 129 I used here for the I-Xe age calculations is most probably correct. Since the 129 I half-life value only affects the relative I-Xe ages, the few Ma relative to the Shallowater standard, the absolute I-Xe ages are almost immune to this uncertainty in the 129 I half-life.

Lunar and Planetary Science Conference, 1973

We report stepwise heating experiments 'on unirradiated and pile-irradiated samples of 14318. Xenon in the unirradiated sample is a nearly homogeneous mixture of fission, spallation, and trapped components, all of which have nearly the same thermal release patterns, peaking strongly at 1200 C. Nevertheless the fission component is slightly enriched relative to the trapped component at low temperatures while the spallation component is slightly enriched at high temperatures. This small separation permits calclllation of the isotopic composition of the fission component; the isotopic compositions of the trapped and spallation component need not be known provided they are homogeneous. The analysis employs a new, three-dimensional, least-squares technique(1). If a particular trapped component, SUCOR(2), is assumed, the definition of the fission component is improved. The "rich component subtraction method" previously employed on 14301(3) yields similar results, as shown in Table 1:

Journal of the Mass Spectrometry Society of Japan, 2004

Improvements in ion collectors of the VG3600 mass spectrometer used for 40 Ar῍ 39 Ar dating in the Radioisotope Center, University of Tokyo, have been performed. We also constructed a new compact vacuum line for extraction and purification of noble gases, and connected it to the mass spectrometer. The new noble gas mass spectrometry system enables us to measure all noble gases (He, Ne, Ar, Kr, and Xe) at low detection limits corresponding to 2῎10 ῌ15 cm 3 STP or 5῎10 3 atoms of Kr and Xe. A newly designed W-coil furnace e#ectively heats small samples (1῍100 mg) in a Mo-crucible with condition of low blank levels (10 ῌ10 and 10 ῌ15 cm 3 STP for Ar and Xe). Smaller sample sizes required for 40 Ar῍ 39 Ar dating have reduced activity levels. The system was preliminarily applied to I῍Xe dating of neutron irradiated meteorites, Bjurböle, Allende and Yamato-74191, and discovered a late formation age of Yamato-74191 (26 Ma after Bjurböle) compared with the Allende meteorite. 129 Xe/ 132 Xe῏ 129 Xe t / 132 Xe῍P (128 Xe t / 132 Xe) ῌP (128 Xe/

Chinese Science Bulletin, 1997

Science, 2021

The origin of r-process elements Theoretical models predict that the synthesis of heavy elements by the rapid neutron capture process (r-process) occurs in extreme astrophysical environments such as neutron star mergers or some types of supernovae. Testing those predictions by comparing them with the isotopic record has been difficult. Côté et al. examined two r-process isotopes, iodine-129 and curium-247, both of which have half-lives of 15.6 million years. Therefore, their ratio remains constant even long after the nucleosynthesis event. The ratio of those isotopes at the time of Solar System formation is recorded in meteorites. Comparing this value with nuclear astrophysics calculations shows that the most likely source was moderately neutron-rich material ejected from a binary neutron star merger. Science , this issue p. 945

Physical Review C, 2021

Earth and Planetary Science Letters, 1974

A new method to date uranium-bearing minerals exclusively by means of a mass spectrometric determination of Xe and/or Kr isotopic ratios has been developed and experimentally tested. It is based on the compositional differences between Xe produced by spontaneous fission of 2 3 8~ in nature and Xe from fission induced by thermal neutrons in a nuclear reactor. Xe is extracted in 5 -10 release fractions at successively higher temperatures.

Geochimica et Cosmochimica Acta, 1988

The iodine-xenon systems of six Allende inclusions (five Eggs and the Pink AngeI) appear to have been altered by non-nebular secondary processes. Evidence for this includes temperature-ordered variations in the initial I isotopic composition within several objects (with older apparent I-Xe ages associated with higher extraction temperatures) and the absence of primitive I-Xe ages. The span of apparent ages seen in Allende objects (10 Ma or more) is probably too long to reflect any nebular process, so at least some alteration probably occurred on the parent body. The range in initial 244Pu/238U ratios for the Eggs (3-14 X 10e3) includes the current best estimates of the bulk solar system value (4-7 X 10F3). For Eaa 3. the Pu/U ratio varies bv a factor oftwo between extractions, probably the result of fractionation of Pu from U among different phases. XNTRODUCTION

Proceedings of the National Academy of Sciences, 2013

Refractory inclusions [calcium-aluminum-rich inclusions, (CAIs)] represent the oldest Solar System solids and provide information regarding the formation of the Sun and its protoplanetary disk. CAIs contain evidence of now extinct short-lived radioisotopes (e.g., 26 Al, 41 Ca, and 182 Hf) synthesized in one or multiple stars and added to the protosolar molecular cloud before or during its collapse. Understanding how and when short-lived radioisotopes were added to the Solar System is necessary to assess their validity as chronometers and constrain the birthplace of the Sun. Whereas most CAIs formed with the canonical abundance of 26 Al corresponding to 26 Al/ 27 Al of ∼5 × 10 −5 , rare CAIs with fractionation and unidentified nuclear isotope effects (FUN CAIs) record nucleosynthetic isotopic heterogeneity and 26 Al/ 27 Al of <5 × 10 −6 , possibly reflecting their formation before canonical CAIs. Thus, FUN CAIs may provide a unique window into the earliest Solar System, including the origin of short-lived radioisotopes. However, their chronology is unknown. Using the 182 Hf-182 W chronometer, we show that a FUN CAI recording a condensation origin from a solar gas formed coevally with canonical CAIs, but with 26 Al/ 27 Al of ∼3 × 10 −6 . The decoupling between 182 Hf and 26 Al requires distinct stellar origins: steady-state galactic stellar nucleosynthesis for 182 Hf and late-stage contamination of the protosolar molecular cloud by a massive star(s) for 26 Al. Admixing of stellar-derived 26 Al to the protoplanetary disk occurred during the epoch of CAI formation and, therefore, the 26 Al-26 Mg systematics of CAIs cannot be used to define their formation interval. In contrast, our results support 182 Hf homogeneity and chronological significance of the 182 Hf-182 W clock. meteorite inclusions | short-lived radionuclides | Solar System formation

Earth and Planetary Science Letters, 2014

Calcium-aluminum-rich inclusions (CAIs) are primitive objects that formed within the protoplanetary disk surrounding the young Sun. Recent Pb-Pb chronologic studies have demonstrated that CAIs are the oldest solar system solids, crystallizing 4567 Ma ago (Amelin et al., 2002; Connelly et al., 2012). The isotope systematics of CAIs therefore provide critical insight into the earliest history of the Solar System. Although Sm-Nd and Rb-Sr geochronometers are highly effective tools for investigating cosmochemical evolution in the early Solar System, previous studies of CAIs have revealed evidence for isotopically disturbed systems. Here we report new age data for Allende CAI Al3S4 derived from both the long-lived (147 Sm-143 Nd) and short-lived (146 Sm-142 Nd) isotopic systems. The 147 Sm-143 Nd chronometer yields an age of 4560 ± 34 Ma that is concordant with 207 Pb-206 Pb ages for CAIs and indicates that the Sm-Nd system was not significantly disturbed by secondary alteration or nucleosynthetic processes. The slope of the 146 Sm-142 Nd isochron defines the Solar System initial 146 Sm/ 144 Sm of 0.00828 ± 0.00044. This value is significantly different from the value of 0.0094 determined by Kinoshita et al (2012). Ages recalculated from all published 146 Sm-142 Nd isochron data using the traditional 103 Ma half-life and the initial 146 Sm/ 144 Sm value determined here closely match Pb-Pb and 147 Sm-143 Nd ages determined on the same samples. In contrast, ages recalculated using the 68 Ma half-life determined by Kinoshita et al. (2012) and either of the initial 146 Sm/ 144 Sm values are often anomalously old. This is particularly true for the youngest samples with 146 Sm-142 Nd isochron ages that are most sensitive to the choice of 146 Sm half-life used in the age calculation. In contrast to the Sm-Nd isotope system, the Rb-Sr system is affected by alteration but yields an apparent isochron with a slope corresponding to a much younger age of 4247 ± 110 Ma. Although the Rb-Sr system in CAIs appears to be disturbed, the initial 87 Sr/ 86 Sr value determined from the isochron is 0.698942 ± 0.000008, and closely approximates estimates of the initial Solar System value. Although this isochron may be a mixing line, it might also record alteration on the Allende parent body in which Rb was added to the Al3S4 CAI that was initially largely devoid of Rb.