Natural plutonium from supernovaeThe rapid neutron capture process (r-process) produces many of the heavy chemical elements, but the astrophysical settings where it occurs remain unclear. Leading ...candidates are neutron star mergers and some types of supernovae. Wallner et al. analyzed the plutonium content of a deep-sea crust sample, identifying a few dozen atoms of the r-process isotope plutonium- 244 that were delivered to Earth within the past few million years. There was a simultaneous signal of iron-60, which is known to be produced in supernovae. Comparing the ratios of these isotopes constrains the relative contributions of supernovae and neutron star mergers to r-process nucleosynthesis.Science, this issue p. 742Half of the chemical elements heavier than iron are produced by the rapid neutron capture process (r-process). The sites and yields of this process are disputed, with candidates including some types of supernovae (SNe) and mergers of neutron stars. We search for two isotopic signatures in a sample of Pacific Ocean crust—iron-60 (60Fe) (half-life, 2.6 million years), which is predominantly produced in massive stars and ejected in supernova explosions, and plutonium-244 (244Pu) (half-life, 80.6 million years), which is produced solely in r-process events. We detect two distinct influxes of 60Fe to Earth in the last 10 million years and accompanying lower quantities of 244Pu. The 244Pu/60Fe influx ratios are similar for both events. The 244Pu influx is lower than expected if SNe dominate r-process nucleosynthesis, which implies some contribution from other sources.
Nuclides synthesized in massive stars are ejected into space via stellar winds and supernova explosions. The solar system (SS) moves through the interstellar medium and collects these nucleosynthesis ...products. One such product is 60Fe, a radionuclide with a half-life of 2.6 My that is predominantly produced in massive stars and ejected in supernova explosions. Extraterrestrial 60Fe has been found on Earth, suggesting close-by supernova explosions ∼2 to 3 and ∼6 Ma. Here, we report on the detection of a continuous interstellar 60Fe influx on Earth over the past ∼33,000 y. This time period coincides with passage of our SS through such interstellar clouds, which have a significantly larger particle density compared to the local average interstellar medium embedding our SS for the past few million years. The interstellar 60Fe was extracted from five deep-sea sediment samples and accelerator mass spectrometry was used for single-atom counting. The low number of 19 detected atoms indicates a continued but low influx of interstellar 60Fe. The measured 60Fe time profile over the 33 ky, obtained with a time resolution of about ±9 ky, does not seem to reflect any large changes in the interstellar particle density during Earth’s passage through local interstellar clouds, which could be expected if the local cloud represented an isolated remnant of the most recent supernova ejecta that traversed the Earth ∼2 to 3 Ma. The identified 60Fe influx may signal a late echo of some million-year-old supernovae with the 60Fe-bearing dust particles still permeating the interstellar medium.
Half of the chemical elements heavier than iron are produced by the rapid neutron capture process (r-process). The sites and yields of this process are disputed, with candidates including some types ...of supernovae (SNe) and mergers of neutron stars. We search for two isotopic signatures in a sample of Pacific Ocean crust-iron-60 (
Fe) (half-life, 2.6 million years), which is predominantly produced in massive stars and ejected in supernova explosions, and plutonium-244 (
Pu) (half-life, 80.6 million years), which is produced solely in r-process events. We detect two distinct influxes of
Fe to Earth in the last 10 million years and accompanying lower quantities of
Pu. The
Pu/
Fe influx ratios are similar for both events. The
Pu influx is lower than expected if SNe dominate r-process nucleosynthesis, which implies some contribution from other sources.
Nuclides synthesized in massive stars are ejected into space via stellar winds and supernova explosions. The solar system (SS) moves through the interstellar medium and collects these nucleosynthesis ...products. One such product is
Fe, a radionuclide with a half-life of 2.6 My that is predominantly produced in massive stars and ejected in supernova explosions. Extraterrestrial
Fe has been found on Earth, suggesting close-by supernova explosions ∼2 to 3 and ∼6 Ma. Here, we report on the detection of a continuous interstellar
Fe influx on Earth over the past ∼33,000 y. This time period coincides with passage of our SS through such interstellar clouds, which have a significantly larger particle density compared to the local average interstellar medium embedding our SS for the past few million years. The interstellar
Fe was extracted from five deep-sea sediment samples and accelerator mass spectrometry was used for single-atom counting. The low number of 19 detected atoms indicates a continued but low influx of interstellar
Fe. The measured
Fe time profile over the 33 ky, obtained with a time resolution of about ±9 ky, does not seem to reflect any large changes in the interstellar particle density during Earth's passage through local interstellar clouds, which could be expected if the local cloud represented an isolated remnant of the most recent supernova ejecta that traversed the Earth ∼2 to 3 Ma. The identified
Fe influx may signal a late echo of some million-year-old supernovae with the
Fe-bearing dust particles still permeating the interstellar medium.
Cosmogenic He, Ne, and Ar as well as the radionuclides 10Be, 26Al, 36Cl, 41Ca, 53Mn, and 60Fe have been determined on samples from the Gebel Kamil ungrouped Ni‐rich iron meteorite by noble gas mass ...spectrometry and accelerator mass spectrometry (AMS), respectively. The meteorite is associated with the Kamil crater in southern Egypt, which is about 45 m in diameter. Samples originate from an individual large fragment (“Individual”) as well as from shrapnel. Concentrations of all cosmogenic nuclides—stable and radioactive—are lower by a factor 3–4 in the shrapnel samples than in the Individual. Assuming negligible 36Cl decay during terrestrial residence (indicated by the young crater age <5000 years; Folco et al. ), data are consistent with a simple exposure history and a 36Cl‐36Ar cosmic ray exposure age (CRE) of approximately (366 ± 18) Ma (systematic errors not included). Both noble gases and radionuclides point to a pre‐atmospheric radius >85 cm, i.e., a pre‐atmospheric mass >20 tons, with a preferred radius of 115–120 cm (50–60 tons). The analyzed samples came from a depth of approximately 20 cm (Individual) and approximately 50–80 cm (shrapnel). The size of the Gebel Kamil meteoroid determined in this work is close to estimates based on impact cratering models combined with expectations for ablation during passage through the atmosphere (Folco et al. , ).
Coulomb explosion of BeO− molecular ions – Revisited Fifield, L.K.; Suter, M.; Froehlich, M.B. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
20/May , Letnik:
538
Journal Article
Recenzirano
Accelerator mass spectrometry (AMS) measurements of 10Be almost invariably utilize the BeO- molecular negative ion. Molecular ions experience the process of ‘Coulomb explosion’ when dissociated by a ...stripper in the high-voltage terminal of a tandem accelerator, resulting in energy and angular spread of the subsequently-accelerated positive ions. In this paper, the phenomenon is studied in detail for both foil and gas stripping of BeO, using the 14UD pelletron accelerator at the Australian National University operating at 8.5 MV. In a companion paper by Suter et al. 1, a model is developed to interpret, inter alia, these results.
The molecular hydride negative ions of mass 129 amu, 127IH2−, 127ID− and 128TeH−, have been studied in order better to understand potential backgrounds in AMS measurements of 129I. All three of these ...ions appear to be stable or, if metastable, to have lifetimes that are sufficiently long to allow at least some of them to reach the high voltage terminal of the accelerator. It is found, however, that these make only a minor contribution to the combined rate of 127I7+ and 128Te7+ ions that pass around the analysing magnet when it is set for 129I7+ detection. The principal contribution comes instead from the injection of 127I− ions into the accelerator along with the 129I− ions, despite the use of a low Cs sputtering energy in the ion source that was intended to eliminate them. This contribution is, however, small and is effectively removed by a Wien filter. In addition, a sample of Woodward iodine, obtained from the University of Arizona, was found to have an 129I/127I ratio of (13.3 ± 0.9) × 10−15. This is the lowest ratio so far reported. In contrast, the batch of Woodward iodine that was being used as an iodine carrier in our laboratory was found to have a much higher ratio of (78.2 ± 2.4) × 10−15. A search for a lower ratio blank failed to find a suitable material.
Accelerator Mass Spectrometry (AMS) at the Department of Nuclear Physics and Accelerator Applications (Australian National University) is based on a 14UD tandem accelerator. The 14UD has demonstrated ...exceptional accelerator performance over more than three decades of AMS, e.g. by running regularly above 14 MV. We present the actual performance for the whole range of measured radionuclides and the potential of this specialised high-energy AMS facility - demonstrating the continuing need for such a system. Focus here will be also on the unique setup comprising an Enge split-pole spectrograph used as a gas-filled magnet (GFM). The GFM has seen growing importance at ANU over the years as a means for providing an efficient reduction of isobaric background. We use the Enge now routinely for 10Be, 26Al, 32Si, 53Mn and 60Fe measurements.
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