A Krypton-81 half-life determination using a mass separator
Abstract
The half-life of 81Kr was determined with the aid of a mass separator equipped with a current integrator. In each experiment a natural krypton sample was irradiated with neutrons to produce 81Kr. After determining the 81–82 atom ratio with a conventional mass spectrometer, the sample was processed in the mass separator, the mass 81 beam being collected in aluminium foil while the mass 82 fraction was collected simultaneously in the Faraday cup of the current integrator. The number of atoms of 81Kr collected in the aluminium foil was calculated from the 81–82 atom ratio and the integrated current of 82Kr. The disintegration rate of these atoms was determined by counting the bromine K X-rays produced in the electron-capture decay of 81Kr using a NaI scintillation spectrometer and thus the half-life was deduced. Tests using natural krypton mixed with 11 y 85Kr showed that ±3% accuracy can be achieved with the current integrator. The average of six determinations of the half-life was 2.13 × 105 y with an estimated experimental error ±5%. However, when the uncertainty in the 81Kr decay energy (250±90 keV) was included the error was increased, giving , a value that agrees with the only previous measurement and is more accurate.
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Cited by (19)
Nuclear Data Sheets for A = 81
2008, Nuclear Data SheetsNuclear structure data pertaining to all nuclei with mass number A = 81 (Zn, Ga, Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb) have been compiled and evaluated and incorporated into the ENSDF data file. This publication for A = 81 supersedes the previous publication (Coral M. Baglin, Nuclear Data Sheets 79, 447 (1996), literature cutoff 1 November 1996) and the subsequent updates by C. Baglin for 81Y (literature cutoff 8 October 1998) and 81Zr (literature cutoff 24 March 2000). All literature available prior to 15 August 2008 has been considered. Subsequent to previous A = 81 evaluations, excited states have been reported for the first time in 81Ga, and knowledge of excited state properties for 81Y and 81Zr has been significantly expanded. However, the expected decay of 81Zr has yet to be studied.
Noble gas and oxygen isotope studies of aubrites: A clue to origin and histories
2007, Geochimica et Cosmochimica ActaNoble gas measurements were performed for nine aubrites: Bishopville, Cumberland Falls, Mayo Belwa, Mount Egerton, Norton County, Peña Blanca Spring, Shallowater, ALHA 78113 and LAP 02233. These data clarify the origins and histories, particularly cosmic-ray exposure and regolith histories, of the aubrites and their parent body(ies). Accurate cosmic-ray exposure ages were obtained using the 81Kr–Kr method for three meteorites: 52 ± 3, 49 ± 10 and 117 ± 14 Ma for Bishopville, Cumberland Falls and Mayo Belwa, respectively. Mayo Belwa shows the longest cosmic-ray exposure age determined by the 81Kr–Kr method so far, close to the age of 121 Ma for Norton County. These are the longest ages among stony meteorites. Distribution of cosmic-ray exposure ages of aubrites implies 4–9 break-up events (except anomalous aubrites) on the parent body. Six aubrites show “exposure at the surface” on their parent body(ies): (i) neutron capture 36Ar, 80Kr, 82Kr and/or 128Xe probably produced on the respective parent body (Bishopville, Cumberland Falls, Mayo Belwa, Peña Blanca Spring, Shallowater and ALHA 78113); and/or (ii) chondritic trapped noble gases, which were likely released from chondritic inclusions preserved in the aubrite hosts (Cumberland Falls, Peña Blanca Spring and ALHA 78113). The concentrations of 128Xe from neutron capture on 127I vary among four measured specimens of Cumberland Falls (0.5–76 × 10−14 cm3STP/g), but are correlated with those of radiogenic 129Xe, implying that the concentrations of (128Xe)n and (129Xe)rad reflect variable abundances of iodine among specimens. The ratios of (128Xe)n/(129Xe)rad obtained in this work are different for Mayo Belwa (0.045), Cumberland Falls (0.015) and Shallowater (0.001), meaning that neutron fluences, radiogenic 129Xe retention ages, or both, are different among these aubrites. Shallowater contains abundant trapped Ar, Kr and Xe (2.2 × 10−7, 9.4 × 10−10 and 2.8 × 10−10 cm3STP/g, respectively) as reported previously (Busemann and Eugster, 2002). Isotopic compositions of Kr and Xe in Shallowater are consistent with those of Q (a primordial noble gas component trapped in chondrites). The Ar/Kr/Xe compositions are somewhat fractionated from Q, favoring lighter elements. Because of the unbrecciated nature of Shallowater, Q-like noble gases are considered to be primordial in origin. Fission Xe is found in Cumberland Falls, Mayo Belwa, Peña Blanca Spring, ALHA 78113 and LAP 02233. The majority of fission Xe is most likely 244Pu-derived, and about 10–20% seems to be 238U-derived at 136Xe. The observed (136Xe)Pu corresponds to 0.019–0.16 ppb of 244Pu, from which the 244Pu/U ratios are calculated as 0.002–0.009. These ratios resemble those of chondrites and other achondrites like eucrites, suggesting that no thermal resetting of the Pu–Xe system occurred after ∼4.5 Ga ago. We also determined oxygen isotopic compositions for four aubrites with chondritic noble gases and a new aubrite LAP 02233. In spite of their chondritic noble gas signatures, oxygen with chondritic isotopic compositions was found only in a specimen of Cumberland Falls (Δ17O of ∼0.3‰). The other four aubrites and the other two measured specimens of Cumberland Falls are concurrent with the typical range for aubrites.
Noble gases, <sup>81</sup>Kr-Kr exposure ages and <sup>244</sup>Pu-Xe ages of six eucrites, Bereba, Binda, Camel Donga, Juvinas, Millbillillie, and Stannern
1998, Geochimica et Cosmochimica ActaNoble gases including radioactive 81Kr (t1/2 = 2.1 × 105 yr) have been measured for the cumulate eucrite Binda and five noncumulate eucrites, Béréba, Camel Donga, Juvinas, Millbillillie, and Stannern, some of which have been repeatedly analyzed. Concentrations of 81Kr, which range from 4.2 × 10−14 to 3.2 × 10−13 cm3 STP/g, roughly correlate with abundances of the main target elements, Sr, Y, and Zr. 81Kr-Kr cosmic-ray exposure ages are obtained as 24.5 ± 0.6 Ma, 21.0 ± 1.6 Ma, 36.6 ± 1.4 Ma, 10.6 ± 0.8 Ma, 20.8 ± 0.5 Ma and 35.1 ± 0.7 Ma, for Béréba, Binda, Camel Donga, Juvinas, Millbillillie, and Stannern, respectively. All the measured eucrites have 244Pu-derived fission Xe. On the basis of fission 136Xe concentrations, 244Pu abundances are calculated to range from 0.40 ppb for Binda to 1.08 ppb for Juvinas. Following the method proposed by Shukolyukov and Begemann (1996a), 244Pu-Xe ages relative to the absolute crystallization age of 4.5578 Ga for Angra dos Reis are determined as −46 ± 18 Ma (Béréba), −29 ± 34 Ma (Binda), −51 ± 16 Ma (Camel Donga), −10 ± 23 Ma (Juvinas), +8 ± 24 Ma (fine-grained portion of Millbillillie), −51 ± 21 Ma (coarse-grained portion of Millbillillie), and −124 ± 13 Ma (Stannern), which correspond to absolute ages ranging from 4.434 Ga (Stannern) to 4.566 Ga (fine-grained portion of Millbillillie). Millbillillie is a mixture of materials with different 244Pu-Xe ages. Stannern’s unusually young 244Pu-Xe age might reflect a secondary shock disturbance, but otherwise, it tends to confirm a distinctive mode of igneous petrogenesis in comparison to most other eucrites. The 244Pu-Xe ages of the cumulate eucrites obtained so far (Binda, this work; Moore County, Shukolyukov and Begemann, 1996a) do not differ systematically from those of noncumulate eucrites. The four eucrites with the older 244Pu-Xe ages, Béréba, Binda, Juvinas, and the fine-grained portion of Millbillillie, show significant amounts of radiogenic 129Xe, (0.6–2.3) × 10−12 cm3 STP/g (after correction for fission 129Xe), which imply earlier retention of radiogenic 129Xe from extinct 129I than other eucrites with young 244Pu-Xe ages.
Nuclear data sheets for A = 81
1996, Nuclear Data SheetsAbstracts:Nuclear structure data pertaining to all nuclei with mass number A=81 have been compiled and evaluated and incorporated into the ENSDF date file.General Policies and Organization of Material:See the January issue of Nuclear Data Sheets.General Comments:This publication for A=81 supersedes the previous (full) publication (J. Müller,Nuclear Data Sheets46,487 (1985)) and the subsequent update (C. Baglin,Nuclear Data Sheets69,267 (1993)), and includes all literature available prior to November 1, 1996.Cutoff Date:All data available prior to November 1, 1996 have been evaluated.Acknowledgments:The author is indebeted to H. Schnare for making data available at very short notice prior to publication. The advice and assistance received from B. Singh (McMaster University), who prepared the superdeformed band data for81Sr and who reviewed the material added to the A=81 chain since its 1993 revision, are also gratefully acknowledged. Throughout this evaluation, the adopted energy for a level seen only in reactions in which no γ rays were observed has been obtained from a weighted average of all data which can reasonably be associated with that level alone, unless noted otherwise. Uncertainties in absolute γ-ray intensities are calculated using the method of Browne (86Br21).
Nuclear data sheets update for A = 81*
1993, Nuclear Data SheetsNuclear structure data pertaining to all nuclei with mass number A = 81 have been compiled and evaluated, and incorporated into the ENSDF data file. Only new or significantly revised data sets are published here, together with all adopted level and adopted γ-ray information for all A = 81 isobars. This publication for A = 81 may be used in conjunction with the previous (full) publication (J. Müller, Nuclear Data Sheets46, 487 (1985) (85Mu16), cutoff date July 1985); please note, however, that data sets which are not published here may, nevertheless, have been revised in the current ENSDF file. The ENSDF file also includes the data set for a post-deadline reference (S. Mitarai, et al., Kyushu University Tandem Accelerator Report, 1991-1992, p. 75) reporting 81Y collective level structure deduced from 58Ni(28Si,αpγ) and 58Ni(32S,2αpγ)) reactions.
<sup>81</sup>Kr terrestrial ages and grouping of Yamato eucrites based on noble gas and chemical compositions
1993, Geochimica et Cosmochimica ActaThe ages and the groupings of Yamato eucrites recovered in Antarctica as well as terrestrial ages of nine Yamato eucrites were determined based on cosmic-ray produced noble gases, including the radionuclide 81Kr. The terrestrial ages of Y-792511, Y-793164, and Y-794043 are 0.14, 0.11, and 0.28 Ma, respectively. Due to the relatively long storage time in ice, the Ce anomaly caused by the terrestrial alteration was significant in these three eucrites. Short terrestrial ages of < 0.08 Ma and long cosmic-ray exposure ages of about 65 Ma, as well as similar noble gas and REE compositions for six eucrites, Y-75011, -791826, -793547, -793548, -793570, and -794002, strongly suggest that they belong to a single fall. For these eucrites, negative Eu anomalies were found. Considering the data of Yamato eucrites previously reported, ≥1 fall(s) are required for monomict and ≥5 falls for polymict eucrites during the past 0.3 Ma. Fissiogenic Xe from 244Pu was observed in nine eucrites, in which the concentration of 244Pu at the beginning of Xe retention was calculated to be (0.5–2.2) ppb. The 244Pu/Nd weight ratio of (1.1–2.1) × 10−4 agrees with that reported for Angra dos Reis (244Pu/Nd = 1.5 × 10−4) within 40%. 244Pu/U ratios of Y-793164 and Y-793548 are 0.0027 ± 0.0004 and 0.0045 ± 0.0011, respectively, assuming the U abundances occurred at 4.5 Ga ago. These ratios are somewhat lower than the ratio of 0.004–0.007 for the solar system.