Speaker
Description
The radionuclide $^{60}$Fe(t$_{1/2}$ = 2.6 Myr) is a tracer for recent nucleosynthesis in massive stars and core-collapse supernovae, whereas the longer-lived radionuclide $^{244}$Pu (t$_{1/2}$ = 81 Myr) is synthesized in the astrophysical r-process. The nucleosynthesis site of the r-process is heavily debated in the astrophysics community with rare supernovae and neutron star mergers being the prime candidate sites.
In contrast to freshly synthesised $^{60}$Fe, $^{244}$Pu, due to its much longer half-life, could accumulate in the interstellar medium over geological timescales. A time-resolved profile of $^{60}$Fe and $^{244}$Pu abundances would provide important information about the site of the r-process and interstellar medium dynamics. The r-process nuclide $^{247}$Cm (t$_{1/2}$ = 15.6 Myr) with a shorter half-life than $^{244}$Pu could additionally serve as an independent clock for r-process nucleosynthesis in the galaxy when compared to $^{244}$Pu.
The search for $^{60}$Fe and $^{244}$Pu on Earth with AMS resulted in the discovery of both interstellar radionuclides. Two distinct global influxes of interstellar $^{60}$Fe around 2.4 Myr [e.g. 1,2] and 7 Myr ago [e.g. 2,4] into marine archives, a recent $^{60}$Fe influx into Antarctic snow [3] as well as a corresponding influx of interstellar $^{244}$Pu into a marine ferromanganese crust [4] were reported. The time-resolution of the $^{244}$Pu profile was so far insufficient to fully relate the influx characteristics of $^{244}$Pu to that of $^{60}$Fe. Up to now, no interstellar $^{247}$Cm has been detected on Earth.
In this contribution, we report on a new time-profile of $^{60}$Fe and $^{244}$Pu in a Pacific ferromanganese crust. The acquired $^{60}$Fe profile shows two pronounced peaks of $^{60}$Fe influxes with improved timing. A continuous r-process $^{244}$Pu influx was discovered with a time-resolution of 1 Myr over the last 10 Myr owing to the extraordinarily high total efficiency of Pu AMS of 1% achieved in this project. Recent work on detecting interstellar $^{247}$Cm in the same archive will be presented.
[1] Knie et. al., Phys. Rev. Lett. 93 (2004).
[2] Wallner et al., Nature 532 (2016).
[3] Koll et al., Phys. Rev. Lett. 123 (2019).
[4] Wallner et al., Science 372 (2021).
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