Speaker
Description
The intermediate neutron-capture process (i process) produces a distinct pattern of rare isotopes at neutron densities between the s and r process. Two candidate sites with predicted rapid mass ejections in the solar neighborhood are post-AGB stars undergoing very-late thermal pulses (e.g. Sakurai's object) and rapidly-accreting white dwarfs (RAWDs). Our 1D and 3D simulations show that the convective-reactive fluid dynamics driving i-process nucleosynthesis leads to violent, non-radial outbursts that eject radioactive material. We calculate ejected yields for isotopes with gamma-ray lines in the 0.5–2 MeV range, including $^{22}$Na, $^{89}$Sr, $^{95}$Zr, and $^{137}$Cs. We estimate that the probability of detecting i-process gamma-ray emission during COSI's prime mission is up to ~1%, rising to ~11% for $^{89}$Sr if the event is caught within days, and ~5% for long-lived $^{22}$Na. Detection of neutron-rich $^{137}$Cs would provide the first direct gamma-ray signature distinguishing intermediate neutron-density nucleosynthesis from s- and r-process pathways, opening a new multi-messenger window on dynamic stellar nucleosynthesis. Future $\gamma$-ray telescopes employing focusing Laue or Fresnel lenses, or liquid-Ar all-sky detectors, could achieve a fiftyfold sensitivity improvement and raise detection probabilities to several tens of percent.
| Career stage | Tenured mid-to-late-career researcher |
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