Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Earth is exposed to nearby cosmic events. The solar system moves through the interstellar medium and collects interstellar dust particles that contain unique signatures of ongoing nucleosynthesis in nearby supernovae or rare cosmic explosions. Such particles may accumulate over million years in deep-ocean archives and in lunar soil, imprinting isotopic fingerprints of specific interstellar radionuclides in the geological record. The most prominent radionuclides are 60Fe (t1/2=2.6 Myr) and 244Pu (81 Myr). Both do not exist naturally on Earth. They can be measured with high sensitivity via accelerator mass spectrometry (AMS). Indeed, both nuclides have been found on Earth or the Moon.
AMS measurements of 60Fe from terrestrial and lunar archives demonstrate a clear exposure of Earth to recent (<10 Myr) cosmic explosions, suggesting close-by supernova activity ~2–3 and ~6 million years ago. In addition, recent detection of interstellar 244Pu, exclusively produced by the rapid neutron capture (r-)process, allows to link supernovae and r-process. This latter process is far from being fully understood. Interstellar 244Pu can place constraints on r-process frequency and production yields over the last few 100 Myr. The measured 244Pu influx was found lower than expected if supernovae dominate r-process nucleosynthesis, implying contributions from additional sources.
In this chapter we follow the journey of such radionuclides after production in massive stars or compact objects, from the interstellar medium to their incorporation in geological archives, resulting finally in the detection of a few atoms via a direct atom counting. These experimental results provide unique insights into recent and nearby nucleosynthesis events.