New Nuclear Reaction Flow duringr‐Process Nucleosynthesis in Supernovae: Critical Role of Light, Neutron‐rich Nuclei

Abstract

We study the role of light neutron-rich nuclei during r-process nucleosynthesis in supernovae. Most previous studies of the r-process have concentrated on the reaction flow of heavy unstable nuclei. Although the nuclear reaction network includes a few thousand heavy nuclei, only limited reaction flow through light-mass nuclei near the stability line has been used in those studies. However, in a viable scenario of the r-process in neutrino-driven winds, the initial condition is a high-entropy hot plasma consisting of neutrons, protons, and electron-positron pairs experiencing an intense flux of neutrinos. In such environments light-mass nuclei as well as heavy nuclei are expected to play important roles in the production of seed nuclei and r-process elements. Thus, we have extended our fully implicit nuclear reaction network so that it includes all nuclei up to the neutron drip line for Z ≤ 10, in addition to a larger network for Z ≥ 10. In the present nucleosynthesis study, we utilize a wind model of massive SNeII explosions to study the effects of this extended network. We find that a new nuclear-reaction flow path opens in the very light neutron-rich region. This new nuclear reaction flow can change the final heavy-element abundances by as much as an order of magnitude.

Astrophysical reaction rate for α(αn,γ)9Be by photodisintegration

“…These possible implications should be studied in detail by using the present new reaction rate. It is to be clarified quantitatively if the α(αn, γ) 9 Be reaction path still predominates the seed production and to what extent the final r-process yields may change by including the present reaction rate and also newly-identified competing reactions 6,7] in the nuclear reaction network.…”

“…The necessary expansion time is determined in comparison with the reaction time scale of the ααn reaction [4]. A more recent study reveals that the reaction flow can go through the neutron-rich region of light elements in the rapidly expanding wind [6,7]. Therefore, the competition of the ααn reaction with other bypass reactions in the short expansion time should be carefully considered.…”

R-process nucleosynthesis in core-collapse supernova explosion

“…However, we have recently found [18,19] that even light neutron-rich nuclei progressively play the significant roles in the production of seed nuclei. The nuclear reaction network used in the previous studies [3,11] included only limited number of light unstable nuclei, 3 H, 7 Be, 8,9 B, 11,14 C, 13 N, 15 O, 18,20 F, 23,24 Ne, and so on.…”

“…There are plenty of protons and α-particles as well as neutrons at this epoch, and the main reaction flow is triggered by 4 Figure 4. Extended nuclear reaction network for explosive nucleosynthesis [19]. For α-process conditions at earlier times the main reaction flows are triggered by the 4 He(αn, γ) 9 Be reaction and two flow paths (4) and (5) follow.…”

Structure and Decay Pattern of Linear-Chain States in Neutron-Rich Carbon Isotopes

“…Light neutron-rich nuclei play an important role in r-process nucleosynthesis [1,2]. The excited states of light nuclei manifest strong α clustering and have been studied for a long time.…”