Speaker
Description
Earth is exposed to nearby cosmic events. Freshly produced radionuclides in the interstellar medium contain information about how and where the heavy elements are made in nature. The solar system moves through the interstellar medium (ISM) and collects interstellar dust particles that contain fresh nucleosynthetic signatures, including the radionuclides Fe-60 (t${_{1/2}}$=2.6 Myr) and Pu-244 (t${_{1/2}}$=81 Myr) or Cm-247 (t${_{1/2}}$=15.7 Myr). These nuclides are incorporated into terrestrial archives over millions of years.
Detection of interstellar nuclides remains extremely challenging and so far was successful only with Accelerator Mass Spectrometry (AMS). Recent technical developments have seen an exceptional gain in measurement efficiency and sensitivity for smaller AMS systems, in particular for actinides, including Pu-244 and Cm-247; and more recently for Hf-182 (t${_{1/2}}$=9 Myr). On the other hand, very large accelerators with >10 million volts terminal voltage are required for the identification of small traces of interstellar Fe-60.
Recent data demonstrate a global Fe-60 influx and is evidence for exposure of Earth to recent (<10 Myr) supernova explosions. In addition, search in deep-sea archives and in lunar soil samples provides the first clear detection of interstellar Pu-244, an actinide nuclide exclusively produced by rapid-neutron capture (r-process), supporting the hypothesis that the dominant heavy element r-process nucleosynthesis is a rare process.
Besides new data for the direct search for interstellar signatures, including Fe-60, Pu-244 and the first search for Cm-247, I will also present preliminary results of recent laboratory measurements using AMS for understanding Fe-60 and Hf-182 production in massive stars - predominantly produced via double neutron capture reactions.
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