Supernova-produced ²⁶Al and ⁶⁰Fe in deep-sea sediments from the Indian Ocean

The long-lived radionuclides ²⁶Al (t_1/2 = 0.72 Myr) and ⁶⁰Fe (t_1/2 = 2.6 Myr) 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 [1,2] evidences an ⁶⁰Fe concentration enhancement ~2-3 Myr ago. This radionuclide does not have terrestrial sources and is suggested to originate from one or more SNe [1]. Depth profiles with ~100 individual samples from deep-sea sediment cores (Indian Ocean) are studied to obtain a detailed data set of ²⁶Al and ⁶⁰Fe concentrations within the time period of the ⁶⁰Fe signal in the crust. The targets were measured using accelerator mass spectrometry [3]. 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 [4]. The major source of ²⁶Al is spallogenic production by cosmic-rays in the Earth’s atmosphere. This first full history of precise ²⁶Al and ⁶⁰Fe data over a time period of 2 Myr for two sediment cores is compared to theoretical estimations of a SN-produced radionuclide deposition on Earth considering different nucleosynthesis models and SN signal widths.
[1] Knie et al., Phys. Rev. Lett 93 (2004)
[2] Fitoussi et al., Phys. Rev. Lett 101 (2008)
[3] Wallner er al., this conf.
[4] Feige et al., EPJWC, 63 (2013)