Origin of Plutonium-244 in the Early Solar System

Lugaro, Maria and Lopez, Andres Yague and Soos Benjamin, Benjamin and Coté, Benoit and Pető, Mária and Wehmeyer, Benjamin and Pignatari, Marco (2022) Origin of Plutonium-244 in the Early Solar System. UNIVERSE, 8 (7). ISSN 2218-1997

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Abstract

We investigate the origin in the early Solar System of the short-lived radionuclide Pu-244 (with a half life of 80 Myr) produced by the rapid (r) neutron-capture process. We consider two large sets of r-process nucleosynthesis models and analyse if the origin of Pu-244 in the ESS is consistent with that of the other r and slow (s) neutron-capture process radioactive nuclei. Uncertainties on the r-process models come from both the nuclear physics input and the astrophysical site. The former strongly affects the ratios of isotopes of close mass (I-129/I-127, Pu-244/U-238, and Pu-247/U-235). The I-129/Cm-247 ratio, instead, which involves isotopes of a very different mass, is much more variable than those listed above and is more affected by the physics of the astrophysical site. We consider possible scenarios for the evolution of the abundances of these radioactive nuclei in the galactic interstellar medium and verify under which scenarios and conditions solutions can be found for the origin of Pu-244 that are consistent with the origin of the other isotopes. Solutions are generally found for all the possible different regimes controlled by the interval (delta) between additions from the source to the parcel of interstellar medium gas that ended up in the Solar System, relative to decay timescales. If r-process ejecta in interstellar medium are mixed within a relatively small area (leading to a long delta), we derive that the last event that explains the I-129 and Cm-247 abundances in the early Solar System can also account for the abundance of Pu-244. Due to its longer half life, however, Pu-244 may have originated from a few events instead of one only. If r-process ejecta in interstellar medium are mixed within a relatively large area (leading to a short delta), we derive that the time elapsed from the formation of the molecular cloud to the formation of the Sun was 9-16 Myr.

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