I-Xe Ages and Trapped Xe Compositions

Geochimica et Cosmochimica Acta, 2004

Twenty-two dark inclusions (DIs) from Allende (18), Leoville (2), Vigarano (1) and Efremovka (1) were studied by the I-Xe method. All except two of these DIs (Vigarano 2226 and Leoville LV2) produce well-defined isochrons, and precise I-Xe ages. The Allende DIs formed a tight group about 1.6 Ma older than Shallowater (4.566 Ϯ 0.002 Ga), about 5 Ma older than four previously studied Allende CAIs. Most of the dark inclusions require trapped Xe with less 129 Xe (or more 128 Xe) than conventional planetary Xe (well restricted in composition by Q-Xe or OC-Xe). Studies of an irradiated/unirradiated DI pair from Allende demonstrate that the 128 Xe/ 132 Xe ratio in trapped is normal planetary, so that a 129 Xe/ 132 Xe ratio below planetary seems to be required. Yet, this is not possible given constraints on 129 Xe evolution in the early solar system. Trends among all of the Allende DIs suggest that an intimate mixture of partially decayed iodine and Xe formed a pseudo trapped Xe component enriched in both 129 Xe and 127 I, and subsequently in 128 Xe after n-capture during reactor irradiation. Enrichment in radiogenic 129 Xe, but with a 129 Xe/ 127 I ratio less than that observed in the iodine host phase, places closure of this trapped mixture Ն13 Ma after precipitation of the major iodine-bearing phase. Because the I-Xe isochron is a mixing line between iodine-derived and trapped Xe (pseudo or not), I-Xe ages, given by the slope of this mixing line, are not compromised by the presence of pseudo trapped Xe, and the precision of the I-Xe ages is given by the statistics of the line fit. Copyright

Chinese Science Bulletin, 1997

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

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:

1998

129Xe, from the decay of the now-extinct 16.7 Ma 129I, accumulates in iodine-bearing sites and since most iodine host phases are secondary, the I-Xe system is typically a chronometer for post-formational processes. The validity of the I-Xe chronometer is confirmed by comparison with Pb-Pb ages on phosphate and feldspar separates from twelve meteorites. Phosphate separates are found to be concordant with Pb-Pb for all six samples in which useful LXe data were obtained. Feldspar is a better iodine host than apatite in H chondrites, typically providing good I-Xe isochrons. These too are concordant with the Pb-Pb ages of the corresponding phosphates for five out of six feldspar separates. The exception is/(llegan whose feldspar yields one of the oldest I-Xe ages observed, similar to those for CI and CM magnetites. We attribute this to a more primary mineralization, predating the secondary phosphate from which the comparison Pb-Pb age was obtained. Absolute I-Xe ages, found using the reported Pb-Pb age of Acapulco phosphate provide an absolute I-Xe age of 4.566 • 0.002 Ga for both Shallowater and BjurbSle irradiation standards. This allows relative I-Xe ages to be interpreted in the context of absolute ages.

Physical Review C, 1995

Lifetimes for the lowest three transitions in the nucleus 120 Xe have been measured using the Recoil Distance Technique. Our data indicate that the lifetime for the 2 + 1 → 0 + 1 transition is more than a factor of two lower than the previously adopted value and is in keeping with more recent measurements performed on this nucleus. The theoretical implications of this discrepancy and the possible reason for the erroneous earlier results are discussed. All measured lifetimes in 120 Xe, as well as the systematics of the lifetimes of the 2 + 1 states in Xe isotopes, are compared with predictions of various models. The available data are best described by the Fermion Dynamic Symmetry Model (FDSM).

Physical Review C, 2021

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

2013

We report on an improved measurement of the 2\nu \beta \beta\ half-life of Xe-136 performed by EXO-200. The use of a large and homogeneous time projection chamber allows for the precise estimate of the fiducial mass used for the measurement, resulting in a small systematic uncertainty. We also discuss in detail the data analysis methods used for double-beta decay searches with EXO-200, while emphasizing those directly related to the present measurement. The Xe-136 2\nu \beta \beta\ half-life is found to be 2.165 +- 0.016 (stat) +- 0.059 (sys) x 10^21 years. This is the most precisely measured half-life of any 2\nu \beta \beta\ decay to date.

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences

Iodine-plutonium-xenon isotope systematics have been used to re-evaluate time constraints on the early evolution of the Earth-atmosphere system and, by inference, on the Moon-forming event. Two extinct radionuclides ((129)I, T1/2=15.6 Ma and (244)Pu, T1/2=80 Ma) have produced radiogenic (129)Xe and fissiogenic (131-136)Xe, respectively, within the Earth, the related isotope fingerprints of which are seen in the compositions of mantle and atmospheric Xe. Recent studies of Archaean rocks suggest that xenon atoms have been lost from the Earth&#39;s atmosphere and isotopically fractionated during long periods of geological time, until at least the end of the Archaean eon. Here, we build a model that takes into account these results. Correction for Xe loss permits the computation of new closure ages for the Earth&#39;s atmosphere that are in agreement with those computed for mantle Xe. The corrected Xe formation interval for the Earth-atmosphere system is [Formula: see text] Ma after the...