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1. Shell-model study of weak β-decays relevant to astrophysical processes

   https://doi.org/10.3389/fphy.2024.1434598  

   Suzuki, Toshio; Shimizu, Noritaka (August 2024, Frontiers in Physics)

   Shell-model studies on the weak $\beta$-decay in nuclei relevant to astrophysical processes are carried out. The $\beta$-decay rates, as well as electron-capture rates in the $sd$- $pf$shell induced by Gamow–Teller (GT) transition, are evaluated in astrophysical environments. The weak rates for the Urca pair of nuclei with $A$= 31 in the island of inversion, which are important for the nuclear Urca processes in neutron star crusts, are investigated by shell-model calculations in the $sd$– $pf$shell. The GT strength is evaluated in the $sd$– $pf$shell for selected $\beta$-decays in the $sd$-shell nuclei, and the effects of the expansion of the configuration space on the quenching of the axial–vector coupling are examined. $\beta$-decay rates induced by first-forbidden (FF) transitions are studied by the Behrens–Bühring (BB) method for the isotones with $N$= 126 and compared with the Walecka method. The important role of the electron distortions in the $\beta$-decays of²⁰⁶Hg and²⁰⁷Tl is pointed out. 

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2. Origin of the elements

   https://doi.org/10.1007/s00159-022-00146-x  

   Arcones, Almudena; Thielemann, Friedrich-Karl (December 2023, The Astronomy and Astrophysics Review)

   Abstract What is the origin of the oxygen we breathe, the hydrogen and oxygen (in form of water H 2 O) in rivers and oceans, the carbon in all organic compounds, the silicon in electronic hardware, the calcium in our bones, the iron in steel, silver and gold in jewels, the rare earths utilized, e.g. in magnets or lasers, lead or lithium in batteries, and also of naturally occurring uranium and plutonium? The answer lies in the skies. Astrophysical environments from the Big Bang to stars and stellar explosions are the cauldrons where all these elements are made. The papers by Burbidge (Rev Mod Phys 29:547–650, 1957) and Cameron (Publ Astron Soc Pac 69:201, 1957), as well as precursors by Bethe, von Weizsäcker, Hoyle, Gamow, and Suess and Urey provided a very basic understanding of the nucleosynthesis processes responsible for their production, combined with nuclear physics input and required environment conditions such as temperature, density and the overall neutron/proton ratio in seed material. Since then a steady stream of nuclear experiments and nuclear structure theory, astrophysical models of the early universe as well as stars and stellar explosions in single and binary stellar systems has led to a deeper understanding. This involved improvements in stellar models, the composition of stellar wind ejecta, the mechanism of core-collapse supernovae as final fate of massive stars, and the transition (as a function of initial stellar mass) from core-collapse supernovae to hypernovae and long duration gamma-ray bursts (accompanied by the formation of a black hole) in case of single star progenitors. Binary stellar systems give rise to nova explosions, X-ray bursts, type Ia supernovae, neutron star, and neutron star–black hole mergers. All of these events (possibly with the exception of X-ray bursts) eject material with an abundance composition unique to the specific event and lead over time to the evolution of elemental (and isotopic) abundances in the galactic gas and their imprint on the next generation of stars. In the present review, we want to give a modern overview of the nucleosynthesis processes involved, their astrophysical sites, and their impact on the evolution of galaxies. 

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3. 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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4. 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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5. Progress on nuclear reaction rates affecting the stellar production of ²⁶ Al

   https://doi.org/10.1088/1361-6471/ac9cf8  

   Laird, A M; Lugaro, M; Kankainen, A; Adsley, P; Bardayan, D W; Brinkman, H E; Côté, B; Deibel, C M; Diehl, R; Hammache, F; et al (January 2023, Journal of Physics G: Nuclear and Particle Physics)

   Abstract The radioisotope 26 Al is a key observable for nucleosynthesis in the Galaxy and the environment of the early Solar System. To properly interpret the large variety of astronomical and meteoritic data, it is crucial to understand both the nuclear reactions involved in the production of 26 Al in the relevant stellar sites and the physics of such sites. These range from the winds of low- and intermediate-mass asymptotic giant branch stars; to massive and very massive stars, both their Wolf–Rayet winds and their final core-collapse supernovae (CCSN); and the ejecta from novae, the explosions that occur on the surface of a white dwarf accreting material from a stellar companion. Several reactions affect the production of 26 Al in these astrophysical objects, including (but not limited to) 25 Mg( p , γ ) 26 Al, 26 Al( p , γ ) 27 Si, and 26 Al( n , p / α ). Extensive experimental effort has been spent during recent years to improve our understanding of such key reactions. Here we present a summary of the astrophysical motivation for the study of 26 Al, a review of its production in the different stellar sites, and a timely evaluation of the currently available nuclear data. We also provide recommendations for the nuclear input into stellar models and suggest relevant, future experimental work. 

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