EuroGenesis_Supernova-produced radionuclides and trace-elements (CoDustMas)

We propose within the Collaborative Research Programme `Cosmic Dust as a Diagnostic for Massive Stars` the laboratory study of cosmic dust via accelerator mass spectrometry (AMS) measurements at the Vienna Environmental Research Accelerator (VERA) of the University of Vienna. This project tackles two aspects: (1) the measurement of trace element isotope ratios in presolar nanodiamonds isolated from meteorites (stardust), e.g. isotope ratios of rare-earth elements (REE) and uranium, to extract r-process nucleosynthesis signatures; and (2) the search for live supernova (SN)-produced radionuclides in terrestrial deep-sea archives, more specifically search for the isotopes of e.g. 26Al, 182Hf, 244Pu and 247Cm. Pre-solar grains contain valuable information about the conditions of the conditions and evolution of dust in SN ejecta and remnants. Using the isotopic pattern of stable isotopes, which has been measured with high precision using high-resolution Secondary Ion Mass Spectrometry (SIMS), contributions from the nucleosynthesis processes (s-, p- and r-process) have been obtained. Ultra-sensitive techniques such as accelerator mass spectrometry (AMS) allow the analysis of rare trace elements in presolar dust through isotope ratio measurements being free of molecular isobaric background. This project aims at better understanding of nucleosynthesis and mixing in supernovae through studies of nanodiamonds isolated from meteorites (in cooperation with MPI Mainz, Germany) with state-of-the-art AMS techniques. Such laboratory studies will assess the isotopic signature of SN dust and its chemical nature. Results will be incorporated at MPI Mainz for network calculations of r-process nucleosynthesis. In addition, as dust formed in the ejecta of a SN contains freshly produced long-lived radionuclides, there might be a chance of finding such radionuclides live in dust particles deposited into terrestrial archives. Stellar nucleosynthesis processes and SN dust formation and its transport into the solar system can be traced through the search for live radionuclides in terrestrial archives, like 60Fe, 26Al, 182Hf, and 244Pu using AMS. Similar to the analysis of stable isotopes in presolar grains, AMS techniques at VERA will be exploited in the search for minute traces of such long-lived isotopes. An example is the recent discovery of live 60Fe on the Pacific ocean floor showing that isotopes produced in SN explosions were able to find their way to Earth. The search for other SN-radionuclides like 26Al, 182Hf, 244Pu, or 247Cm at VERA will complement the 60Fe discovery at TU Munich and will provide direct clues on the nucleosynthesis of massive stars. One important issue is the experimental proof of r-process scenarios via the direct observation of nuclides generated in the r-process. We will continue to search for 244Pu (t1/2 = 81 Ma) and 247Cm (t1/2 = 15.6 Ma) in such archives in close collaboration with TU Munich and Hebrew University. Hence, studying the chemical and isotopic composition of stardust extracted both from meteorites and from terrestrial samples, by AMS technique at VERA, is an excellent means to investigate the mixing that takes place during and after SN explosion as well as the nucleosynthesis in the massive progenitor and during the explosive events.

We performed laboratory studies of cosmic dust via ultra-sensitive accelerator mass spectrometry (AMS) measurements at the University of Vienna (VERA), The Australian National University (ANU, Canberra) und at the Helmholtz Centre Dresden-Rossendorf (HZDR). This project tackled two aspects: (1) Trace element isotope ratios in presolar material (stardust), which was kept unchanged since their production prior to the formation of the SS. We studied nanodiamonds (nanometer-sized diamonds) with the extremely sensitive method of AMS at the VERA facility. That material was isolated from meteorites (Murchison and Allende) and investigated for deviations in their Platinum isotope signatures. The study of the isotopic composition of stardust is an excellent method to investigate the nucleo-synthesis processes, mixing time-scales and dust formation during and shortly after a SN explosion. We found some evidence for small abundance deviations for the heaviest isotope, 198Pt, as expected from some SN-models; however, using other meteorite fractions, the results are not fully conclusive yet.(2) The search for live supernova (SN)-produced radionuclides in terrestrial deep-sea archives. Such radionuclides, if produced in a SN event during the last few million years (Myr) and in close distance to the solar system (SS), i.e. within ~300 light years, might be incorporated live into terrestrial archives. Similarly, longer-lived nuclides, present in the interstellar medium, can be trapped in such archives as well over longer time scales. An example is the recent discovery of live 60Fe on the Pacific ocean floor showing that isotopes produced in SN explosions were able to find their way to Earth. The search for SN-produced radionuclides in terrestrial archives was the main emphasis of our studies: (2a) One important aspect is the experimental proof of r-process scenarios via the direct observation of nuclides generated in this process - that is responsible for the production of about half of all heavy elements (above iron). However, we do not know the site and history: candidates are SNe or mergers of neutron stars. We analysed a large deep-ocean crust sample from the Pacific for its content of a long-lived Pu isotope (244Pu, half-life = 81 Myr). This crust had grown extremely slowly over 25 Myr. Using 244Pu we could trace its production back in time over several 100 Myr; reflecting its concentration in the interstellar medium. 244Pu is a perfect marker for studying the r-process (in particular actinide production). Our experimental result, more than 100 more sensitive than previous studies, demonstrates for the first time that actinide production has been very rare during the last few 100 Myr.(2b) We analysed 4 different deep-sea sediments from the Indian Ocean over a time period of 8 Myr. Our main aim was the search for radionuclides produced in a close-by SN. We analysed ~100 samples for any evidence of an extraterrestrial signature of 26Al and 60Fe, both are produced in large quantities in SNe. The samples were measured at VERA (26Al), at HZDR (dating) and 60Fe was measured at the ANU. We found a clear signal of 60Fe with unsurpassed time resolution for the time period between 1.7 and 3.1 million years which confirms a previous first assumption deduced from a less time-resolved measurement in a deeps-sea crust. That 60Fe could not be produced on Earth and is a clear evidence for a SN-activity a few Myr ago in relative proximity to our SS.