Interstellar 60Fe detected on Earth - but where is the r-process nuclide 244Pu?

Interstellar 60Fe detected on Earth - but where is the r-process nuclide 244Pu?

Wallner, A.; Kinoshita, N.; Feige, J.; Froehlich, M.; Hotchkis, M.; Paul, M.; Fifield, L. K.; Golser, R.; Honda, M.; Kivel, N.; Linnemann, U.; Matsuzaki, H.; Merchel, S.; Pavetich, S.; Rugel, G.; Schumann, D.; Tims, S. G.; Steier, P.; Winkler, S. R.; Yamagata, T.

The Interstellar Medium (ISM) is continuously fed with new nucleosynthetic products. The solar system moves through the ISM and collects dust particles. Therefore, direct detection of freshly produced radionuclides on Earth, before decaying, provides insight into recent and nearby nucleosynthesis [1,2]. Indeed, a pioneering work at Munich [3], using AMS for ocean crust-samples, showed an enhanced 60Fe signal of extraterrestrial origin.

Within an international collaboration we have continued to search for ISM radionuclides trapped in deep oceanarchives. We have analyzed sediments, crusts and nodules for extraterrestrial 60Fe (t1/2=2.6 Myr), 26Al (0.7 Myr) and 244Pu (81 Myr) [4-7] complemented by independent work at Munich [8-10]. We demonstrated that multiple events happened in our galactic neighbourhood and left their fingerprint on Earth. A global 60Fe influx is evidence for exposure to recent (<10 Myr) supernova explosions.

The site where the heaviest elements are made in nature is, however, still unknown. The low concentrations measured for 244Pu suggest an unexpectedly low abundance of interstellar 244Pu [5]. It signals a rarity of actinide r-process nucleosynthesis, which is incompatible with the rate and expected yield of supernovae as the predominant actinide-producing sites.

We will present new results for 60Fe measured at the ANU and 244Pu at ANSTO with unprecedented sensitivity.
These data provide new insights into their concomitant influx and their ISM concentrations over a time period of the last 11 Myr.

[1] Korschinek et al., Radiocarbon38 68, ‘96 [2] Ellis et al., ApJ.470 1227, ‘96 [3] Knie et al., PRL83, 18 (‘99) & PRL93 171103, ‘04 [4] Wallner et al., Nature Comm.6 5956, ‘15 [5] Feige et al., EPJ63 3003, ‘13 [6] Wallner et al., Nature532 69, ‘16 [7] Paul et al. ApJL558 L133, ‘01 [8] C. Wallner et al. NAstrRev48, 145150, ‘04 [9] Fimiani et al., PRL16 151104, ‘16 [10] Ludwig et al., PNAS113 9232, ‘16

Keywords: AMS; supernova; interstellar medium

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Publ.-Id: 25521