Freeze-out yields of radioactivities in core-collapse supernovae

TL;DR

This paper investigates how different freeze-out expansion mechanisms in core-collapse supernovae influence nucleosynthesis, identifying two isotope families and demonstrating the effects of non-monotonic profiles on radioactivity production.

Contribution

It introduces non-monotonic freeze-out profiles to study their impact on nucleosynthesis, revealing new isotope production pathways and the significance of reverse shocks and asymmetries.

Findings

Isotopes in 12<=A<=122 form two families with distinct evolutionary profiles.

Non-monotonic profiles enhance radioactivity production compared to monotonic ones.

Reverse shocks and asymmetries significantly influence nucleosynthesis outcomes.

Abstract

We explore the nucleosynthesis trends from two mechanisms during freeze-out expansions in core-collapse supernovae. The first mechanism is related to the convection and instabilities within homogeneous stellar progenitor matter that is accreted through the supernova shock. The second mechanism is related to the impact of the supersonic wind termination shock (reverse shock) within the tumultuous inner regions of the ejecta above the proto-neutron star. Our results suggest that isotopes in the mass range 12<=A<=122 that are produced during the freeze-out expansions may be classified in two families. The isotopes of the first family manifest a common mass fraction evolutionary profile, whose specific shape per isotope depends on the characteristic transition between two equilibrium states (equilibrium state transition) during each type of freeze-out expansion. The first family includes the majority of isotopes in this mass range. The second family is limited to magic nuclei and isotopes in their locality, which do not sustain any transition, become nuclear flow hubs, and dominate the final composition. We use exponential and power-law adiabatic profiles to identify dynamic large-scale and small-scale equilibrium patterns among nuclear reactions. (truncated abstract) In addition, we introduce non-monotonic parameterized profiles to probe the impact of the reverse shock and multi-dimensional explosion asymmetries on nucleosynthesis. Cases are shown in which the non-monotonic profiles favor the production of radioactivities. Non-monotonic freeze-out profiles involve longer non-equilibrium nucleosynthesis intervals compared with the exponential and power-law profiles, resulting in mass fraction trends and yield distributions that may not be achieved by the monotonic freeze-out profiles.