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.
93Zr (t1/2=1.6Ma) is mostly produced by the main s-process in low-to-intermediate mass AGB stars. Large uncertainty exists in the current 92Zr(n,γ)93Zr Maxwellian Average cross section. This could ...have significant impact on nucleosynthesis calculations. Large amounts of 93Zr are also produced in nuclear reactors and pose long-term environmental radioactivity. Hence, measurement of 93Zr by the AMS is important for both fields above. We report here on progress in the development of AMS method to measure 93Zr. Compared with 98MeV beam energy, Zr/Nb isobar position separation was improved using 155.2MeV beam energy and Gas-Filled Magnet. Energy loss measurement with increased beam energy inside the detector indicates that higher beam energy can improve isobar energy loss separation. A chemical procedure to reduce the Nb content in Zr samples has been developed and tested. It reduces the 93Nb content by a factor of 1000.
Fluoride molecular anions have emerged as a potential alternative to oxides for the analysis of actinides in AMS. Research at the Vienna Environmental Research Accelerator (VERA) has focused on ...mixing samples prepared in an Fe2O3 matrix with PbF2 for in situ fluoridation during the sputter process. The relative formation probabilities for a range of (oxy-)fluoride molecular anions of uranium, neptunium, plutonium, and americium have been found to be characteristic for each of the actinides investigated. These data can help to identify isobaric interference for the mentioned actinides. A first application is monitoring of the 236U co-production with 236Np during Th irradiation. Extracting these actinides in the form of tetrafluoride anions allows the suppression of U by an order of magnitude relative to Np.
Selective laser photodetachment of anions is a novel technique for isobar suppression in Accelerator Mass Spectrometry (AMS). Ion-laser interaction times on the order of ms required for near-complete ...isobar suppression are achieved by retarding the ions in a gas-filled radio frequency quadrupole cooler. Inside this RFQ, the cooled anion beam is overlapped collinearly with an intense cw-laser beam. Within the Ion Laser InterAction Mass Spectrometry (ILIAMS) project at the University of Vienna, a dedicated injector beamline has been coupled to the VERA-AMS facility to explore and develop this method. In this work, experimental investigations on ion beam transmission, stability and elemental selectivity of the new setup are presented.
A 532 nm laser at 10 W transmitted power provides suppression factors larger than ten orders of magnitude for S− and MgO− under AMS conditions with simultaneous beam transmission for the ions of interest of up to 80%. The excellent ion identification capabilities of the subsequent AMS system also facilitate the study of destruction and formation of molecular anions inside the ion cooler. These kinetic and chemical reactions with the buffer gas provide additional elemental selectivity in certain cases, whereas others constitute a source of background.
Reassessment of 182Hf AMS measurements at VERA Forstner, O.; Gnaser, H.; Golser, R. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
2011, Letnik:
269, Številka:
24
Journal Article
Recenzirano
The radioisotope
182Hf (
t
1/2
=
8.9
Ma) is of great interest for astrophysical applications as a chronometer for the early solar system or as possible live supernova remnant on earth. However, AMS ...measurements of
182Hf are seriously influenced by the presence of the stable isobar
182W, which cannot be separated at typical AMS energies. Previous studies revealed a possible suppression of
182W against
182Hf by extracting the negatively charged pentafluoride
HfF
5
-
from the ion source, leading to a detection limit for
182Hf/
180Hf in the order of 10
−11. However, this suppression behavior is in contrast to theoretical calculations of the electron affinity and recent measurements using SIMS instruments, where the achieved suppression cannot be reproduced. The aim of our study is to determine the effects of ion source background as well as further investigate the suppression of tungsten against hafnium by extracting negatively charged fluoride ions from different sample materials. The previously reported suppression factor of about 6000 could be increased to 36000 by careful tuning of the ion source using HfF
4 as sample material. The trend of the theoretical electron affinities could be reproduced using atomic tungsten and hafnium instead of HfF
4 as sample material. This supports the assumption that the major contribution of the tungsten background is not sputtered from the target matrix but comes from somewhere else in the ion source. Measurements from the second ion source show a higher background of tungsten and a lower suppression factor, i.e. careful design of the ion source is crucial. Moving the sputter beam over the target surface extending over the wheel holding the targets revealed the highest tungsten background was detected outside the sputter target position. Further investigations are necessary to locate the origin of the tungsten background in the ion source. Possible sources are the material used for the ion source construction or contaminations in the cesium used for sputtering.
An advanced radio-frequency quadrupole (RFQ) ion cooler was developed for accelerator mass spectrometry to use element-selective laser photodetachment and ion-molecule reactions for isobar ...suppression. The system will be installed as a central part of the new Anion Laser Isobar Separator (ALIS) at the 6 MV AMS system of CologneAMS.
The new RFQ design intends to solve the technical challenge of the deceleration and trapping of heavy molecular ion beams with high emittance. Therefore, an elliptical injection electrode was developed to slow down the ions far away from the central entrance aperture. A new and easy-to-manufacture guide-field assembly was developed. For this purpose, diagonally-split cylindrical surface electrodes are capacitively coupled to a core rod that is carrying the RF signal. Consequently, only low DC voltages are needed to create a gradually changing potential in the longitudinal direction. The RFQ and the acceleration electrodes are installed in a self-aligned structure.
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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