Multiple radionuclide study of a recent supernova event in deep-sea sediments with AMS

Long-lived radionuclides such as ²⁶Al, ⁵³Mn, and ⁶⁰Fe are generated in massive stars and ejected into space by stellar winds and explosions. If a star ends its life in a supernova (SN) explosion close to the solar system, a fraction of these elements might be deposited in terrestrial archives. Recent analysis of a ferromanganese crust [1], fossilized bacteria in deep-sea sediments [2] and lunar samples [3] evidence a ⁶⁰Fe concentration enhancement ~2-3 Myr ago, suggesting to originate from one or more SNe [1].
We expanded this work to a comprehensive and detailed study of a full set of SN-related radionuclides. Detailed depth profiles of ¹⁰Be, ²⁶Al, ⁵³Mn and ⁶⁰Fe concentrations were measured at three different AMS laboratories for ~100 individual samples from four deep-sea sediment cores from the Indian Ocean. In contrast to our ⁶⁰Fe data, which shows a clear signal without terrestrial background, a possible ²⁶Al signal from a SN event is hidden within a non-negligible terrestrial background production. The major source of ²⁶Al is spallogenic production by cosmic-rays in the Earth's atmosphere.
We obtained isotope ratios ²⁶Al/²⁷Al of ~10^-14 with regularly <10% statistical uncertainty [4]. This allowed us to generate for the first time a full history of precise ²⁶Al data over a time period of 2 Myr for two sediment cores revealing an unexpected smooth depth dependence. We took advantage of it and applied the ²⁶Al/²⁷Al ratio as an independent and enhanced dating tool, comparable to ¹⁰Be/⁹Be but without needing stable isotope measurements. Comparative measurements of ¹⁰Be/⁹Be at the DREAMS and VERA facilities show a very good agreement (~5 %).
[1] Knie et al., Phys. Rev. Lett 93, 2004, [2] Ludwig et al., AMS-13, [3] Fimiani et al., LPSC 1659, 2012, [4] Feige et al., EPJWC,63 2013