Astrophysics and Meteorites

Where do the chemical elements come from? Nuclear astrophysics is the discipline to answer this question by reproducing conditions of the early universe and stars on Earth and by establishing reliable models for nucleosynthesis of isotopes and chemical enrichment of galaxies.

Accelerator Mass Spectrometry is used to directly search for nucleosynthesis products in the form of long-lived radionuclides in geological samples. Directly related to the search in geological samples is the establishment of production rates and irradiation histories of meteorites with long-lived isotopes. Another application is the "activation + AMS" approach to determine astrophysical reaction cross-sections, complementary to online in-beam facilities.

Applications

Search for interstellar radionuclides produced in nearby supernovae. AMS is used for the direct detection of nucleosynthesis products on Earth. The long-lived radionuclide ⁶⁰Fe (half-life of 2.6 Myr) is not abundant on Earth. It is dominantly produced in stars by stellar burning and supernovae and by cosmic-ray spallation in meteorites and cosmic dust. Searches for ⁶⁰Fe in ferromanganese crusts and nodules, deep-sea sediments, lunar rock and Antarctic snow showed that there have been several interstellar ⁶⁰Fe influxes in the past and continues until today. In collaboration with the AMS group of ANU at the Heavy Ion Accelerator facility in Canberra, we are successfully detecting ⁶⁰Fe from recent supernovae in several samples, and this collaboration is currently the only research group world-wide capable in doing so.

Constrain the sites of the astrophysical r-process. We also focus on the long-lived radionuclide ²⁴⁴Pu (half-life of 81 Myr), which is produced in the astrophysical r-process. The detection of a concomitant influx of stellar nuclides (e.g. ⁶⁰Fe) and r-process nuclides (e.g. ²⁴⁴Pu or ²⁴⁷Cm) may link supernovae and the various candidates for r-process sites. The goal is to establish a history of interstellar radionuclide influxes with different half-lives as chrono-markers and different origins to understand how the solar neighbourhood was formed, how stellar explosions impact the Earth and most importantly where the heavy elements in the universe are formed.

Irradiation histories and production rates in meteorites. The group is working on identifying and categorising meteorites by their radionuclide inventory to establish a global meteorite database. For the radionuclides ⁵³Mn and ⁶⁰Fe the group has been leading work that provided more than 2/3 of the global meteorite data. Meteorites have been used to distinguish between interstellar and interplanetary ⁶⁰Fe by the knowledge of production rates of cosmogenic radionuclides. Constancy of galactic cosmic ray intensity as well as irradiation histories of single meteorites can be studied with the help of long-lived radionuclides in and out of equilibrium.

Astrophysical reaction cross-sections. Besides the direct search for nucleosynthesis products on Earth, the group works on one of the main experimental inputs for nuclear models, namely cross-sections for charged particle and neutron induced reactions. Stellar particle energies can be simulated in accelerator based irradiation facilities after the irradiation of samples. AMS is then used to determine the ratio between the seed isotope and the reaction product, which allows to determine the cross section for astrophysical environments.

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User Information

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Projects and Collaborations

Joint PhD student with the Australian National University (Dominik Koll, start 2018): A 10-million year time profile of interstellar influx to Earth mapped through supernova 60Fe and r-process 244Pu Supported by the Australian Institute of Nuclear Science and Engineering (AINSE) PhD student (Sebastian Zwickel, start 2022): Interstellar and cosmogenic radioisotopes on the surface of the Moon Collaborations with the Australian National University (for 60Fe), Australia's Nuclear Science and Technology Organisation (for 244Pu and 247Cm) and the University of Vienna (for 182Hf)

Further Reading

Fundamentals

Iliadis, C. (2015). Nuclear Physics of Stars. Wiley https://doi.org/10.1002/9783527692668 Xilu W., Clark, A.M., Ellis, J., Ertel, A.F., Fields, B.D., Fry, B.J., Liu, Z., Miller, J.A. and Surman, R. (2021). r-Process radioisotopes from near-Earth supernovae and kilonovae. The Astrophysical Journal, 923(2), p. 219. https://doi.org/10.3847/1538-4357/ac2d90 Ellis, J., Fields, B.D. and Schramm, D.N. (1996). Geological isotope anomalies as signatures of nearby supernovae. The Astrophysical Journal, 470, 1227. https://doi.org/10.1086/177945

Own publications (see also here)

Wallner, A., Feige, J., Kinoshita, N., Paul, M., Fifield, L. K., Golser, R., Honda, M., Linnemann, U., Matsuzaki, H., Merchel, S., Rugel, G., Tims, S.G., Steier, P., Yamagata, T. and Winkler, S.R. (2016). Recent near-Earth supernovae probed by global deposition of interstellar radioactive 60Fe. Nature, 532, 69–72. https://doi.org/10.1038/nature17196 Koll, D., Korschinek, G., Faestermann, T., Gómez-Guzmán, J.M., Kipfstuhl, S., Merchel, S. and Welch, J.M. (2019). Interstellar 60Fe in Antarctica. Physical Review Letters, 123(072701). https://doi.org/10.1103/PhysRevLett.123.072701 Wallner, A., Froehlich, M.B., Hotchkis, M.A.C., Kinoshita, N., Paul, M., Martschini, M., Pavetich, S., Tims, S.G., Kivel, N., Schumann, D., Honda, M., Matsuzaki, H. and Yamagata, T. (2021). 60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae. Science, 372(6543). https://doi.org/10.1126/science.aax3972 Bischoff, A., Alexander, C.M. O'D., Barrat, J.-A., Burkhardt, C., Busemann, H., Degering, D., Di Rocco, T., Fischer, M., Fockenberg, T., Foustoukos, D.I., Gattacceca, J., Godinho, J.R.A., Harries, D., Heinlein, D., Hellmann, J.L., Hertkorn, N., Holm, A., Jull, A.J.T., Kerraouch, I., King, A.J., Kleine, T., Koll, D., Lachner, J., Ludwig, T., Merchel, S., Mertens, C.A.K., Morino, P., Neumann, W., Pack, A., Patzek, M., Pavetich, S., Reitze, M.P., Rüfenacht, M., Rugel, G., Schmidt, C., Schmitt-Kopplin, P., Schönbächler, M., Trieloff, M., Wallner, A., Wimmer, K. and Wölfer, E. (2021). The old, unique C1 chondrite Flensburg – Insight into the first processes of aqueous alteration, brecciation, and the diversity of water-bearing parent bodies and lithologies. Geochimica et Cosmochimica Acta, 293, 142-186. https://doi.org/10.1016/j.gca.2020.10.014 Feige, J., Wallner, A., Fifield, L.K., Merchel, S., Rugel, G., Steier, P., Tims, S.G., Winkler, S.R. and Golser, R. (2018). Limits on 60Fe/26Al nucleosynthesis ratios from deep-sea sediment AMS measurements. Physical Review Letters 121, 221103. https://doi.org/10.1103/PhysRevLett.121.221103 Wallner, A., Feige, J., Fifield, L.K., Froehlich, M.B., Golser, R., Hotchkis, M.A.C., Koll, D., Leckenby, G., Martschini, M., Merchel, S., Panjkov, S., Pavetich, S., Rugel, G., Tims, S.G. (2020). 60Fe deposition during the late Pleistocene and the Holocene echoes past supernova activity. Proceedings of the National Academy of Sciences (PNAS) 201916769. https://doi.org/10.1073/pnas.1916769117