Limits on ⁶⁰Fe/²⁶Al nucleosynthesis ratios from deep-sea AMS measurements

The long-lived radionuclide ²⁶Al (t_1/2=~0.7 Myr) has been observed throughout our galaxy, reflecting ongoing nucleosynthesis over the past few million years [1]. It is produced and ejected into the interstellar medium by stellar winds and during supernova explosions. A nearby supernova may leave an imprint of ²⁶Al in terrestrial archives, complementing the observation of supernova-produced ⁶⁰Fe in deep-sea samples. The same set of sediment samples from the Indian Ocean that showed a distinct ⁶⁰Fe-signature in layers of ages between 1.7 and 3.2 Myr [2] was also analyzed for ²⁶Al. However, additional terrestrial sources producing ²⁶Al on Earth, such as cosmogenic production in the atmosphere and in-situ production within the sediment, may obscure a supernova imprint. We used our experimental ²⁶Al data to infer lower limits on ⁶⁰Fe/²⁶Al nucleosynthesis ratios by comparing the width and the strength of the previously measured ⁶⁰Fe-signal to our ²⁶Al data. We find that our results generally favour the higher theoretical isotopic supernova ratios and deviate from the observed galactic ⁶⁰Fe/²⁶Al flux ratio by 2-3 times of the measurement uncertainty.

[1] Diehl et al., New Astron. Rev., 52, 440 (2008)
[2] Wallner, Feige et al., Nature, 532, 69 (2016)