Thu·Jan 23, 2020Thursday·January 23, 2020

1. 01*

   Investigation of the one-neutron transfer in ${}^{13}$C + ${}^{28}$Si at E${}_{lab}$ = 30 and 34 MeV

   R. Linares · C. C. Seabra · V. A. B. Zagatto🇧🇷 · V. Scarduelli · L. Gasques · L. C. Chamon · B. R. Gonçalves · D. R. Mendes Junior · A. Lépine-Szily

   Background: Neutron transfer measurements for the ${}^{18}$O + ${}^{28}$Si system have shown that the experimental one-neutron and two-neutron transfer cross sections are well reproduced with spectroscopic amplitudes from two different shell model interactions for the Si isotopes: \textit{psdmod} for the two-neutron transfer, and \textit{psdmwkpn} for the one-neutron transfer. Purpose: The origin of this ambiguity can be related to a more complex mechanism in the one-neutron transfer that requires the unpairing of neutrons prior to its transfer in the (${}^{18}$O,${}^{17}$O) reaction. Studying a nucleus where this characteristic is absent (${}^{13}$C) should help to elucidate this question. Method: One-neutron transfer cross sections were measured for the ${}^{13}$C + ${}^{28}$Si at E${}_{lab}$ = 30, and 34 MeV, and compared with coupled reaction channel calculations using spectroscopic amplitudes derived from the \textit{psdmod} and \textit{psdmwkpn} shell model interactions. Results: The spectroscopic amplitudes from the \textit{psdmod} interaction for the relevant states in ${}^{29}$Si provide a good description of the experimental data and the corresponding values agree with previous estimates obtained from the (d,p) reaction. Conclusions: The experimental data for the one-neutron transfer to ${}^{28}$Si induced by (${}^{13}$C,${}^{12}$C) reaction is well reproduced using spectroscopic amplitudes from the \textit{psdmod}.

   nucl-exnucl-thPRC(2020)·10 citations
2. 02*

   Decay properties of ${}^{22}\mathrm{Ne}+\alpha$ resonances and their impact on $s$-process nucleosynthesis

   S. Ota🇯🇵 · G. Christian🇨🇦 · G. Lotay🇬🇧 · W. N. Catford🇬🇧 · E. A. Bennett · S. Dede🇺🇸 · D. T. Doherty🇫🇷 · S. Hallam🇨🇦 · J. Hooker🇺🇸 · C. Hunt🇺🇸 · H. Jayatissa🇺🇸 · A. Matta🇬🇧 and 6 other authors

   The astrophysical $s$-process is one of the two main processes forming elements heavier than iron. A key outstanding uncertainty surrounding $s$-process nucleosynthesis is the neutron flux generated by the ${}^{22}\mathrm{Ne}(\alpha ,n){}^{25}\mathrm{Mg}$ reaction during the He-core and C-shell burning phases of massive stars. This reaction, as well as the competing ${}^{22}\mathrm{Ne}(\alpha ,\gamma ){}^{26}\mathrm{Mg}$ reaction, is not well constrained in the important temperature regime from $\sim 0.2$--$0.4$~GK, owing to uncertainties in the nuclear properties of resonances lying within the Gamow window. To address these uncertainties, we have performed a new measurement of the ${}^{22}\mathrm{Ne}({}^6\mathrm{Li},d){}^{26}\mathrm{Mg}$ reaction in inverse kinematics, detecting the outgoing deuterons and ${}^{25,26}\mathrm{Mg}$ recoils in coincidence. We have established a new $n/\gamma$ decay branching ratio of $1.14(26)$ for the key $E_x=11.32$ MeV resonance in ${}^{26}\mathrm{Mg}$, which results in a new $(\alpha ,n)$ strength for this resonance of $42(11)\mu$eV when combined with the well-established $(\alpha ,\gamma )$ strength of this resonance. We have also determined new upper limits on the $\alpha$ partial widths of neutron-unbound resonances at $E_x=11.112,$ $11.163$, $11.169$, and $11.171$ MeV. Monte-Carlo calculations of the stellar ${}^{22}\mathrm{Ne}(\alpha ,n){}^{25}\mathrm{Mg}$ and ${}^{22}\mathrm{Ne}(\alpha ,\gamma ){}^{26}\mathrm{Mg}$ rates, which incorporate these results, indicate that both rates are substantially lower than previously thought in the temperature range from $\sim 0.2$--$0.4$~GK.

   nucl-exastro-ph.SRnucl-thPLB(2020)·26 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.