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1. Beyond-mean-field calculations of allowed and first-forbidden β − decays of r -process waiting-point nuclei

   https://doi.org/10.1051/epjconf/202226003002  

   Robin, Caroline ; Litvinova, Elena ; Martínez-Pinedo, Gabriel ( January 2022 , EPJ Web of Conferences)

   Liu, W. ; Wang, Y. ; Guo, B. ; Tang, X. ; Zeng, S. (Ed.)

   β -decay rates of neutron-rich nuclei, in particular those located at neutron shell closures, play a central role in simulations of the heavy-element nucleosynthesis and resulting abundance distributions. We present β -decay half-lives of even-even N = 82 and N = 126 r -process waiting-point nuclei calculated in the approach based on relativistic quasiparticle random phase approximation with quasiparticle-vibration coupling. The calculations include both allowed and first-forbidden transitions. In the N = 82 chain, the quasiparticlevibration coupling has an important impact close to stability, as it increases the contribution of Gamow-Teller modes and improves the agreement with the available data. In the N = 126 chain, we find the decay to proceed dominantly via first-forbidden transitions, even when the coupling to vibrations is included. 

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2. Weak Interaction Physics at TwinSol

   https://doi.org/10.1051/epjconf/202125203001  

   Kolata’, J. J. ; Brodeur, Maxime ; Ahn, Tan ; Bardayan, Dan ; O’Malley, Patrick ; Randhawa, J. S. ( January 2021 , EPJ Web of Conferences)

   Pakou, A. ; Bonatsos, D. ; Lalazissis, G. ; Souliotis, G. (Ed.)

   A program to investigate the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix by studying super-allowed mixed mirror β decays has been initiated at the TwinSol facility at Notre Dame. These mixed Fermi/Gamow-Teller (F-GT) decays, occurring between T=1/2 isospin doublets in mirror nuclei, provide a complimentary check on the data from super-allowed pure Fermi decays from 0 + to 0 + states. The first part of the program, involving the measurement of the lifetimes of the relevant nuclei to the required accuracy of one part in 10 3 or better, has nearly been completed. However, the additional complication introduced by F-GT mixing requires the use of an ion trap to measure the mixing ratio ρ with similar accuracy. The lifetime measurements, as well as progress in installing an ion trap at TwinSol , will be discussed. In addition, since the ion trap will require a dedicated beam line for its operation, an opportunity presented itself to greatly improve the performance of TwinSol for reaction studies with exotic nuclei. This took the form of an added dipole switching magnet coupled to a third solenoid to form the new TriSol facility currently under construction. The expected properties of TriSol , and its application to reaction studies of interest for nuclear astrophysics, will also be discussed. 

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3. Constraining the Rapid Neutron-Capture Process with Meteoritic I-129 and Cm-247

   Cote, B. ; Eichler, M. ; Yagüe, A. ; Vassh, N. ; Mumpower, M.R. ; Világos, B. ; Soós, B. ; Arcones, A. ; Sprouse, T.M. ; Surman, R. ; et al ( June 2020 , ArXivorg)

   Meteoritic analysis demonstrates that radioactive nuclei heavier than iron were present in the early Solar System. Among them, 129I and 247Cm both have a rapid neutron-capture process (r process) origin and decay on the same timescale (≃ 15.6 Myr). We show that the 129I/247Cm abundance ratio in the early Solar System (438±184) is immune to galactic evolution uncertainties and represents the first direct observational constraint for the properties of the last r-process event that polluted the pre-solar nebula. We investigate the physical conditions of this event using nucleosynthesis calculations and demonstrate that moderately neutron-rich ejecta can produce the observed ratio. We conclude that a dominant contribution by exceedingly neutron-rich ejecta is highly disfavoured. 

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4. Impact of systematic nuclear uncertainties on composition and decay heat of dynamical and disc ejecta in compact binary mergers

   https://doi.org/10.1093/mnras/stad1458  

   Kullmann, I. ; Goriely, S. ; Just, O. ; Bauswein, A. ; Janka, H-T ( May 2023 , Monthly Notices of the Royal Astronomical Society)

   Theoretically predicted yields of elements created by the rapid neutron capture (r-)process carry potentially large uncertainties associated with incomplete knowledge of nuclear properties and approximative hydrodynamical modelling of the matter ejection processes. We present an in-depth study of the nuclear uncertainties by varying theoretical nuclear input models that describe the experimentally unknown neutron-rich nuclei. This includes two frameworks for calculating the radiative neutron capture rates and 14 different models for nuclear masses, β-decay rates, and fission properties. Our r-process nuclear network calculations are based on detailed hydrodynamical simulations of dynamically ejected material from NS–NS or NS–BH binary mergers plus the secular ejecta from BH–torus systems. The impact of nuclear uncertainties on the r-process abundance distribution and the early radioactive heating rate is found to be modest (within a factor of ∼20 for individual A > 90 abundances and a factor of 2 for the heating rate). However, the impact on the late-time heating rate is more significant and depends strongly on the contribution from fission. We witness significantly higher sensitivity to the nuclear physics input if only a single trajectory is used compared to considering ensembles with a much larger number of trajectories (ranging between 150 and 300), and the quantitative effects of the nuclear uncertainties strongly depend on the adopted conditions for the individual trajectory. We use the predicted Th/U ratio to estimate the cosmochronometric age of six metal-poor stars and find the impact of the nuclear uncertainties to be up to 2 Gyr.

    

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5. The impact of (n,γ) reaction rate uncertainties of unstable isotopes on the i -process nucleosynthesis of the elements from Ba to W

   https://doi.org/10.1093/mnras/stab772  

   Denissenkov, Pavel A ; Herwig, Falk ; Perdikakis, Georgios ; Schatz, Hendrik ( April 2021 , Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT The abundances of neutron (n)-capture elements in the carbon-enhanced metal-poor (CEMP)-r/s stars agree with predictions of intermediate n-density nucleosynthesis, at Nn ∼ 1013–1015 cm−3, in rapidly accreting white dwarfs (RAWDs). We have performed Monte Carlo simulations of this intermediate-process (i-process) nucleosynthesis to determine the impact of (n,γ) reaction rate uncertainties of 164 unstable isotopes, from 131I to 189Hf, on the predicted abundances of 18 elements from Ba to W. The impact study is based on two representative one-zone models with constant values of Nn = 3.16 × 1014 and 3.16 × 1013 cm−3 and on a multizone model based on a realistic stellar evolution simulation of He-shell convection entraining H in a RAWD model with [Fe/H] = −2.6. For each of the selected elements, we have identified up to two (n,γ) reactions having the strongest correlations between their rate variations constrained by Hauser–Feshbach computations and the predicted abundances, with the Pearson product–moment correlation coefficients |rP| > 0.15. We find that the discrepancies between the predicted and observed abundances of Ba and Pr in the CEMP-i star CS 31062−050 are significantly diminished if the rate of 137Cs(n,γ)138Cs is reduced and the rates of 141Ba(n,γ)142Ba or 141La(n,γ)142La increased. The uncertainties of temperature-dependent β-decay rates of the same unstable isotopes have a negligible effect on the predicted abundances. One-zone Monte Carlo simulations can be used instead of computationally time-consuming multizone Monte Carlo simulations in reaction rate uncertainty studies if they use comparable values of Nn. We discuss the key challenges that RAWD simulations of i process for CEMP-i stars meet by contrasting them with recently published low-Z asymptotic giant branch (AGB) i process. 

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