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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - IPUSS (The initial 244Pu abundance of the Solar System)

Teaser

Summary

The increasing knowledge of the short-lived radioactive isotope systems allows us to decipher the nature and timing of chemical variation during the first few hundred million years following the formation of the Solar System and even to constrain the pre-solar history of the Solar System matter. However, to obtain a consistent picture of the earliest processes, the abundance of each short lived radionuclide at the time of the formation of the Sun has to be inferred with very high accuracy. Plutonium-244 (244Pu) is one of the short-lived radionuclides (with a half-life of 80 million years) that is produced by the rapid neutron-capture process (the r process) within neutron star mergers and rare supernovae.
The goal of the IPUSS 753276 project was to obtain the best estimate of the initial 244Pu content of the Solar System. In addition, the project proposed to use the initial abundance estimate to constrain the time of the last stellar event that added r-process nuclides to the pre-solar nebula. In principle, the 244Pu-Xe system can also be used as chronometer to date early volatile loss events in Solar System solids. IPUSS proposed to evaluate this chronometer using the new uncertainties of the improved estimate.
The main objective regarding transfer of knowledge was to bridge the gap between cosmochemistry and the theoretical astrophysics field of galactic chemical evolution.
PetÅ‘ connected the local team at the Konkoly Observatory to the European community of cosmochemistry. The supervisor Maria Lugaro, who is a leading scientist in stellar evolution and nucleosynthesis, connected PetÅ‘\'s research to already existing research directions on short-lived radioactive nuclei at the institute and integrated PetÅ‘ within the local scientific community in Hungary.

Work performed

Analytical work (see details at project website https://konkoly.hu/staff/peto.maria/IPUSS/):

The IPUSS project studied high metamorphic grade ordinary chondrites, phosphate mineral separates, Calcium Aluminum rich inclusions (CAIs) from CV3 primitive carbonaceous chondrites and differentiated meteorites. Trace element data was obtained on the same sample aliquots destroyed for noble gas analysis. Most data was obtained with quadrupole inductively coupled mass spectrometry and for phosphates with neutron activation analysis. The analytical work also involved successful neutron irradiation of some of the studied samples. The noble gas analysis on CAIs was obtained on exceptionally large amount of material, and Mg isotope analysis was necessary for mapping out nucleosynthetic variations of studied inclusions. Noble gas isotope analysis at the secondment included furnace experiments, laser extraction development and testing, and laser experiments. Noble gas isotope data has been obtained on ordinary chondrites, CAIs and phosphates. Although the dataset for the latter two sample group is incomplete, we have the funds to complete the experiments at the secondment within 8 months from the end date of the MSCA.

Results (including exploitations and dissemination)

1. The project obtained a complementary set of meteorite samples that is for the first time adequate to explain the variation of the initial Pu/U ratio in the early Solar System. The project successfully developed a comprehensive experimental approach that includes high precision noble gas isotope analysis in combination with trace element analysis on the very same samples. The dataset will be published shortly as a first-author paper (PetÅ‘ M. K., Busemann H., Jacobsen S., Wang K., Wehmeyer B,. Sedagatpour F., Lugaro M., Gmeling K., Petaev M., Ott U. A new estimate of the initial 244Pu content of the early Solar System, to be submitted to Geochimica et Cosmochimica Acta)
2. The project mapped the high precision Mg isotopic composition of 22 CAIs, which lead to the unexpected discovery of strong nucleosynthetic anomaly in a â€œFUNâ€ CAI. The finding is unique and exciting because this type of anomalous material could be dated with U-Pb for the first time, and can shed light on the timing of the addition of another short-lived radioactive nucleus 26Al to the pre-solar nebula, whose decay acted as the main heat source in the first few million years. PetÅ‘ has been involved in the Mg and Ca isotopic characterization of the FUN CAI. The result was presented as an invited talk at Goldschmidt Conference in 2018 and will be published as a first-author paper (PetÅ‘ M. K., Sedagatpour., Jacobsen S B. A new type of FUN CAI, to be submitted to Geochimica et Cosmochimica Acta)
3. PetÅ‘ has co-authored an invited review paper in the journal Lithos that summarizes recent observations and the current understanding of the degassing history of the Earthâ€™s mantle. This work is a milestone for her ongoing modeling of terrestrial volatile degassing and the re-evaluation of the Pu-I-Xe chronometry.
(Parai R., et al., 2019, The emerging portrait of an ancient, heterogeneous and continuously evolving plume source. Lithos 346-347, 1-16.)
4. PetÅ‘ has been actively involved in the scientific discussions on the origin of r-process nuclei and galactic chemical evolution within the host group at Konkoly Observatory. She collaborates more closely with Benjamin Wehmeyer, with whom she is developing a simplified Galaxy model that includes some of the recently understood features of heterogeneaous galactic chemical evolution. This model will be used within the paper in preparation to interpret the new 244Pu analytical data.
5. Additional collaborative work of PetÅ‘ with University of St Louis, USA involved characterizing the cosmogenic noble gas nuclide abundances and exposure ages in meteorites suitable for K isotope research (Zhao C., et al., 2019 Potassium isotopic compositions of enstatite meteor

Final results

Combining the seemingly distinct fields of solid Earth geochemistry, cosmochemistry and astrophysics allows to properly interpret the chemical data of meteorites and its diverse implications. Our approach in the IPUSS project greatly improves our understanding of how the short lived radionuclides (including 244Pu investigated by the action) were delivered to the early Solar System. Information on the 244Pu content also constrains the timing of volatile depletion in meteorites and planetary objects. This and similar studies will add extra pieces of the puzzle tracing the origin of material in our Solar System.