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Abstract This review summarizes the state of knowledge of the$$^{12}$$ $_{}^{12}$C+$$^{12}$$ $_{}^{12}$C fusion reaction and its impact on stellar carbon burning environments. 

Abstract We investigate nuclear reactions and feedback in hyperaccreting neutron star environments, considering accretion rates in the range 0.3–3 × 10⁴M_⊙yr⁻¹, typical of short-period compact-object binaries in common envelopes. Our models account for weak reactions, neutrino energy loss, nuclear energy release, pair production, degenerate equations of state, and general relativistic hydrodynamics. Depending on the accretion rates, these systems can develop both proton- and neutron-rich atmospheres with strong convective instabilities linking the neutrino sphere to the outgoing accretion shock inside the radiation trapping zone. Convection drives nucleons through multiple heating and cooling cycles, with photodisintegration dominating during the heating phase and heavy element synthesis during the cooling phase, ejecting material with abundances that depend on the accretion rate and depth of the final decompression trajectory. The turbulent nature of convective currents is conducive to creating a wide range of nuclear products through a variety of effects, including nuclear statistical equilibrium freeze-out and ther-,p-, andγ-processes. We also observe a novel multistep process in reheated trajectories, consisting of proton-capture and photodissociation reactions operating onr-process seeds, producing overall neutron-deficient isotopes. A significant amount of infalling gas experiences high entropy and short (millisecond) freeze-out timescales capable of makingr-process elements with high overabundances through a disequilibrium effect between neutrons andα-particles that does not require an excess of neutrons. 

Abstract Neutron-induced reactions play an important role in fundamental nuclear physics, nuclear astrophysics, and applications. In the case of reactions on rare isotopes, there are limited options for direct experimental measurements. The Neutron Target Demonstrator project at Los Alamos National Laboratory seeks to test the feasibility of moderating spallation neutrons within a 1 m$$^3$$ $_{}^3$graphite cube to create a standing neutron target for neutron-induced reaction measurements in inverse kinematics. This paper presents the results of experimental neutron flux distribution tests using neutron sources (ranging from 1 keV to 50 MeV) created by accelerators at the University of Notre Dame and Texas A&M University. Measurements were made with both the full graphite cube as well as a ”half cube” setup in which half of the graphite cube was removed. The measured distributions agree with simulated distributions in the case of the full cube moderator, although there remain discrepancies in certain cases for the half cube moderator. The results shown here will provide useful information for an upcoming experimental campaign to test the neutron target proof-of-principle. 

Abstract This paper is in memory of Roberto Gallino, a long-time collaborator on questions of neutron sources and neutron-induced reactions in stellar nucleosynthesis. We therefore discuss a topic that was of great interest to him, the correlation between neutron sources that provide the neutron flux for the production of heavy elements in thes-process and neutron poison reactions that reduce the number of neutrons in the stellar environment. Neutron poisons play a role in alls-process environments, such as the final phase of core helium burning of massive stars or the carbon pocket in hydrogen-helium intershell environment of low-mass AGB stars, originally proposed by Gallino and his co-workers more than 40 years ago. This paper will argue that neutron poison reactions serve as a neutron storage mechanism through which neutron sources can be fueled to provide a delayed neutron release. 

Abstract Model-observation comparisons of type-I X-ray bursts (XRBs) can reveal the properties of accreting neutron star systems, including the neutron star compactness. XRBs are powered by nuclear burning, and a handful of reactions have been shown to impact the model results. Reactions in the NiCu cycles, featuring a competition between⁵⁹Cu(p,γ)⁶⁰Zn and⁵⁹Cu(p,α)⁵⁶Ni, have been shown to be among the most important reactions as they are a critical checkpoint inrp-process flow and significantly impact the light curves and burst ashes. We report a direct measurement of⁵⁹Cu(p,α)⁵⁶Ni, bringing stringent constraints on this reaction rate. New results rule out a strong NiCu cycle in XRBs, with a negligible degree of recycling, ≤5% up to 1.5 GK. The new reaction rate, when varied within new uncertainty limits, shows no impact on one-zone XRB model light curves tailored for clocked-bursterGS1826–24, hence removing an important nuclear physics uncertainty in the model-observation comparison. 

Abstract Lifetimes of excited states in$$^{162}$$ $_{}^{162}$Dy were measured using the (n,n’$$\gamma $$ $\gamma$) reaction with the Doppler-Shift Attenuation Method (DSAM) at the University of Kentucky’s Accelerator Laboratory. A total of eighteen level lifetimes were obtained, including eleven negative-parity states, seven of which are new. These measurements significantly expand the experimental database of transition probabilities for negative-parity bands in the well-deformed rare earth region of nuclei. The extracted B(E1) and B(E2) values reveal enhanced interband E1 ($$10^{-3}$$ ${10}^{-3}$or$$10^{-4}$$ ${10}^{-4}$) W.u. and E2 strengths (several W.u.) between negative- and positive parity bands, particularly for the KEquation missing<#comment/>bands decaying to the the K$$^{\pi }=2^+_{\gamma }$$ $_{}^{\pi }=2_{\gamma }^{+}$band, consistent with signatures of octupole-quadrupole coupling. In contrast, the K$$^{\pi }=0^-_1$$ $_{}^{\pi }=0_1^{-}$and K$$^{\pi }=1^-_3$$ $_{}^{\pi }=1_3^{-}$bands, which exhibit strong E1 transitions to the ground state band, are indicative of octupole-vibrational excitations built on the deformed ground state. Comparison of transition rates with Alaga rules supports this interpretation and distinguishes collective excitations from likely quasi-particle states. These new results establish$$^{162}$$ $_{}^{162}$Dy as the most extensively characterized rare-earth nucleus for negative parity lifetimes and provide critical experimental benchmarks for theoretical models. 

Abstract A simple optical model (OPM) method using non-monotonic (NM) potentials characterized by a repulsive core from the microscopic theory of the Pauli-led energy-density functional (EDF) has been developed to investigate the¹⁶O+¹⁶O fusion at sub-Coulomb energies relevant to the oxygen burning. The study involves the analysis of the experimental fusion cross-section (FCS) data in energy range 6.92 ≤E_cm≤ 13.83 MeV, which includes the Coulomb barrier regionE_cm= 10.0–11.92 MeV. Apart from an excellent description of the existing FCS data in the studied energy range, the associated hindrance, characterized by theS-factor reaching a maximum and then gradually falling off at lower energies, so far suggested empirically for the system, is reproduced down to 4 MeV for the first time in the simple OPM. AnS-factor maximum ofS₀ = 3.15 × 10²⁵MeV.b atE₀ = 7.14 MeV is observed withT ≃ 2.6 GK, which conforms to the values reported for quiescent and explosive burning. Our reaction rate, deduced from the NM potential, compares well with the Caughlan and Fowler data. Dominant partial waves implicit in the observed maximumS-factor in the studied Gamow range are also explored. Our present findings, with the success of NM potentials, suggest thatthe nucleus–nucleus potential is non-monotonic. 

Abstract Reactions between atomic nuclei are measured in great detail in terrestrial laboratory experiments; transferring and extrapolating this knowledge to how the same reactions act within cosmic environments presents major challenges. Cross-disciplinary efforts are needed in view of the many nuclear reactions that govern the chemical evolution of the universe, and occur in a broad range of stellar plasma conditions that require astrophysical exploration. The variety of quiescent and explosive astrophysical environments for nuclear processes reaches from Big Bang conditions through stellar interiors to a multitude of explosive processes of and near compact stars. Since the early identification of ’processes’ associated with the buildup of elements or nucleosynthesis, new insights have been obtained on the complexity of nuclear reaction mechanisms. This article will provide an overview in nuclear processing shaped by reactions during near equilibrium conditions, cooling and freeze out times. The emergence of molecular-like nucleon configurations within nuclei incurs important features at the low energies given in stellar interiors. Multiple capture and fusion reactions are key in the overall nucleosynthesis patterns. Here we use$$^{12}$$ $_{}^{12}$C induced capture and fusion processes to illustrate the challenge of low-energy measurements and the challenges of using theoretical methods to extrapolate measurements towards energy regimes within cosmic sources. Slow and rapid neutron captures processes facilitate the gradual buildup of heavy elements. Particle beam experiments at accelerator facilities above and deep underground simulate stellar reactions, and new experimental facilities and methods complement these by providing short-lived isotope-separated beams and high-flux photon and neutron sources in a new generation of laboratories, with laser driven plasma facilities and particle storage rings as the latest tools for the experimenters. This is complemented by improved theoretical tools to calculate the quantum effects of nuclear reactions at the various cosmic conditions. Astronomical signatures of nuclear reactions from within cosmic sources are deduced through a growing range of observational tools. This ranges from the determination of rapidly changing light curves characterizing cosmic explosions from supernova, novae, and kilonovae, through gamma-ray lines and presolar grains to the detection of rare neutrino particles from our Sun to distant cosmic events. High resolution spectroscopy of distant stars has been expanded to objects and transient events measured in the X-ray and the gamma energy range of the electromagnetic spectrum. The analysis of vibrational behavior of stars in astro-seismology provides new tools in probing stellar interiors. The isotopic analysis of meteoritic inclusions provides detailed information about various nucleosynthesis sources, which are important tools for the understanding of complex dynamic convection and mixing processes in the interior of stars. While requiring care in interpreting observational data, to account for various biases and systematics, this variety of tools provides new opportunities and synergies. Chemical-evolution models provide a bridge through stellar-abundance archeology and have recently developed to also describe the complex dynamics during the evolution of galaxies. This article seeks to summarize the efforts to determine experimental and theoretical efforts for a better understanding of the complex mechanisms that lead to the compositional evolution of our universe, supplemented by an overview of the broad range of observational tools that have been developed to test the experimental data and the theoretical interpretation of nuclear processes in the cosmos. 

Abstract This paper reports on the possible role of tritium-induced reactions of light nuclei, which may influence nucleosynthesis in short-lived environments such as the third minute of the Big Bang. They may also play a role during the emergence of the neutrino-driven shock front in core collapse supernovae or merging neutron stars at extreme densities. The production of tritium requires a very dynamic and neutron-rich environment; under such conditions tritium-induced reactions are expected to play an important role in the development of specific reaction patterns that could lead to a delayed release of neutrons influencing the associated nucleosynthesis. Here, we summarize different possible reaction sequences and discuss the strength and impact of tritium cluster resonances that occur near the tritium threshold in the respective compound systems. 

Abstract Carl Friedrich von Weizsäcker published two important papers on topics of nuclear astrophysics in 1937 and 1938 before he turned his attention elsewhere motivated by the discovery of fission and the outbreak of war in 1939. It seems, however, that he continued to actively think about issues related to astrophysics, namely the discussion and role of neutron stars and cosmology. Both are contemporary topics today. This paper presents the development of Weizsäcker’s thoughts in the years between 1935 and 1945, making use of his personal notes and letters.