Single Atom Counting of Stellar and r-Process Nuclei in Time-Resolved Deep-Sea Archives

Stars are the major element factories in the universe. In 1999, live supernova Fe-60 (t1/2 =2.6 Myr) was detected in a deep-sea ferromanganese crust (1 ) indicating the accumulation of supernova dust on Earth about 2 million years ago. This was followed by several projects reinforcing the initial evidence for a global influx of supernova Fe-60. Recently, a much younger continuous influx was found in Antarctic snow and in deep-sea sediments (2 –4 ) and an older peak around 6 - 8 Myr in deep-sea crusts (5 , 6 ). In contrast to the well-known production mechanism and synthesis site of Fe-60, the long-lived plutonium isotope Pu-244 (t1/2 =80 Myr) is a pure r-process nucleus. The nucleosynthesis site for the astrophysical r-process is still debated in the astrophysics community. Potential candidates involve rare supernovae and neutron star mergers. To date no evidence was presented that would point to an exclusive r-process site and combinations of different sites are considered. Experimentally, we can search for Pu-244 signatures in samples with known Fe-60 signatures to test for either common influx patterns or independent Pu-244 influxes disentangled from stellar Fe-60. Accordingly, this information provides a unique and direct experimental approach for identifying the production site of the heavy elements. Based on the recent publication of the first detection of interstellar Pu-244 in a ferromanganese crust with a time resolution of 4.5 Myr (integrating over much shorter Fe-60 influxes) (6 ), we are now working on a highly time-resolved profile of Fe-60 and Pu-244 in the large ferromanganese crust VA13/237KD. This direct experimental input will further constrain models for r-process nucleosynthesis in the galaxy. The recently determined profile of Fe-60 clearly shows two influxes, one at 2 Myr, the other at 7 Myr, confirming and refining previous results. Preliminary data on Pu-244 and an outlook for future measurement campaigns will be given. References 1. K. Knie