Mid Term Review

A 10-million year time profile of interstellar influx to Earth mapped through long-lived Fe-60 and Pu-244

Mr Dominik Koll
Department Nuclear Physics

Where do all the elements on Earth come from?
The lightest elements up to Li-7 are synthesised in the big bang, elements up to Fe in either stellar nucleosynthesis by charged particle fusion or by cosmic-ray spallation. Production of the majority of the elements heavier than the iron group needs, however, free neutrons to surpass the increasing Coulomb barrier for charged particle fusion. The slow neutron-capture process up to the element Bi-209 happens in late stellar burning, but the site for the rapid neutron-capture process, exclusively responsible for the synthesis of all elements heavier than Bi-209 including the actinides, is still unknown. The most promising candidates are rare supernovae such as hypernovae and neutron star mergers. A direct observation of a concomitant influx of stellar synthesised radioisotopes and r-process synthesised actinides onto Earth would be a smoking gun for the stellar r-process in supernovae.

In this talk, I will describe the pioneering work that has been done over the last 20 years to detect live supernova Fe-60 and/or r-process synthesised Pu-244 in deep-sea archives, Antarctic snow and lunar samples by Accelerator Mass Spectrometry (AMS).

Within my project, I will attempt to detect Be-10, Fe-60 and Pu-244 in the largest ferromanganese crust ever used with a time resolution better than 1 Myr to deduce for the first time the temporal signature of interstellar Pu-244 influx onto Earth over the past 20 Myr. This will allow us to distinguish between a constant r-process nuclide abundance in the interstellar medium and peaks of Pu-244 related to supernovae if concomitant with Fe-60 or from other explosive scenarios if independent. Preliminary data of the AMS measurements at ANU, ANSTO and HZDR (Germany) will be presented and the experimental challenges of this project will be highlighted.

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