Neutron-induced reaction rates, including fission, are calculated in the temperature range 1.d8 <T (K) < 1.d10 within the framework of the statistical model for targets with atomic number 83 < Z < 119 (from Po to Uuo) from the neutron to the proton drip-line. Four sets of rates have been calculated, utilizing - where possible - consistent nuclear data for neutron separation energies and fission barriers from Thomas-Fermi (TF), Extended Thomas-Fermi plus Strutinsky Integral (ETFSI), Finite-Range Droplet Model (FRDM) and Hartree-Fock-Bogolyubov (HFB) predictions. Tables of calculated values as well as analytic seven parameter fits in the standard REACLIB format are supplied. We also discuss the sensitivity of the rates to the input, aiming at a better understanding of the uncertainties introduced by the nuclear input.
Within the potential cluster model with Pauli forbidden states the possibility of description of the experimental data on the total radiative n12C- and n13C-capture cross sections in the astrophysical energy range from 25 meV to 1.0 MeV is presented. The E1-transition covers the capture data from the scattering states to the ground one of 13C and 14C nuclei. Capture on the three low laying excited states 1/2+, 3/2- and 5/2+ of 13C was calculated.
In dense astrophysical plasmas, neutron capture populates highly excited nuclear states close to the neutron threshold. The impact of additional low-energy nuclear excitations via coupling to the atomic shell on the ability of the so-formed compound nucleus to retain the captured neutron is investigated. We focus on the mechanism of nuclear excitation by electron capture in plasmas characterized by electron fluxes typical for the slow neutron capture process of stellar nucleosynthesis. The small effect of this further excitation on the neutron capture and gamma decay sequence relevant for nucl…
A small number of naturally occurring, proton-rich nuclides (the p-nuclei) cannot be made in the s- and r-process. Their origin is not well understood. Massive stars can produce p-nuclei through photodisintegration of pre-existing intermediate and heavy nuclei. This so-called gamma-process requires high stellar plasma temperatures and occurs mainly in explosive O/Ne burning during a core-collapse supernova. Although the gamma-process in massive stars has been successful in producing a large range of p-nuclei, significant deficiences remain. An increasing number of processes and sites has been …
Background: The density dependence of nuclear symmetry energy is crucial in determining several properties of finite nuclei to the neutron stars with mass $\sim$ 1.4 $M_\odot$. The values of neutron skin thickness, isovector giant dipole resonances energies and various nuclear reaction cross-sections in asymmetric nuclei have been utilized to determine the slope of symmetry energy ($L_0$) at the saturation density. Recent PREX-II and CREX measurements of neutron skin thickness in $^{208}$Pb and $^{48}$Ca nuclei yield very different values of $L_0$ which overlap marginally within 90$\%$ confide…
Nuclear masses are one of the key ingredients of nuclear physics that go into astrophysical simulations of the $r$ process. Nuclear masses effect $r$-process abundances by entering into calculations of Q-values, neutron capture rates, photo-dissociation rates, beta-decay rates, branching ratios and the properties of fission. Most of the thousands of short-lived neutron-rich nuclei which are believed to participate in the $r$ process lack any experimental verification, thus the identification of the most influential nuclei is of paramount importance. We have conducted mass sensitivity studies n…
Spectral lines belonging to the short-lifetime heavy radioactive elements up to Es ($Z$=99) have been found in the spectra of the Przybylski's star. We suggest that these unstable elements may be decay products of a "magic" metastable nucleus belonging to the the island of stability where the nuclei have a magic number of neutrons $N=184$. The laboratory-produced nuclei have a significantly smaller number of neutrons. To identify spectra of the $N=184$ isotopes of these nuclei and their neutron-reach superheavy decay products in astrophysical data we calculate the isotope shift which should be…
The continued interest to the study of the radiative neutron capture on atomic nuclei is caused, on the one hand, by the important role of this process in the analysis of many fundamental properties of nuclei and nuclear reactions, and, on the other hand, by the wide use of the capture cross section data in the various applications of nuclear physics and nuclear astrophysics, and, also, by the analysis of the processes of primordial nucleosynthesis in the Universe. This review is devoted to description of the results obtained for the processes of the radiative neutron capture at thermal and as…
Captures of alpha particles on the proton-richest Barium isotope, 130Ba, have been studied in order to provide cross section data for the modeling of the astrophysical gamma process. The cross sections of the 130Ba(alpha,gamma)134Ce and 130Ba(alpha,n)133Ce reactions have been measured with the activation technique in the center-of mass energy range between 11.6 and 16 MeV, close above the astrophysically relevant energies. As a side result, the cross section of the 132Ba(alpha,n)135Ce reaction has also been measured. The results are compared with the prediction of statistical model calculation…
Neutrino-driven winds following core collapse supernovae have been proposed as a suitable site where the so-called light heavy elements (between Sr to Ag) can be synthetized. For moderately neutron-rich winds, ($α,n$) reactions play a critical role in the weak r process, becoming the main mechanism to drive nuclear matter towards heavier elements. In this paper we summarize the sensitivity of network-calculated abundances to the astrophysical conditions, and to uncertainties in the ($α,n$) reaction rates. A list of few ($α,n$) reactions were identified to dominate the uncertainty in the calcul…
Astrophysical S-factors of radiative capture reactions on light nuclei have been calculated in a two-cluster potential model, taking into account the separation of orbital states by the use of Young schemes. The local two-body potentials describing the interaction of the clusters were determined by fitting scattering data and properties of bound states. The many-body character of the problem is approximatively accounted for by Pauli forbidden states. An important feature of the approach is the consideration of the dependence of the interaction potential between the clusters on the orbital Youn…
We add an ensemble of nuclei to the equation of state for homogeneous nucleonic matter to generate a new set of models suitable for astrophysical simulations of core-collapse supernovae and neutron star mergers. We implement empirical constraints from (i) nuclear mass measurements, (ii) proton-proton scattering phase shifts, and (iii) neutron star observations. Our model is also guided by microscopic many-body theory calculations based on realistic nuclear forces, including the zero-temperature neutron matter equation of state from quantum Monte Carlo simulations and thermal contributions to t…
Rare information on photodisintegration reactions of nuclei with mass numbers $A \approx 160$ at astrophysical conditions impedes our understanding of the origin of $p$-nuclei. Experimental determination of the key ($p,γ$) cross sections has been playing an important role to verify nuclear reaction models and to provide rates of relevant ($γ,p$) reactions in $γ$-process. In this paper we report the first cross section measurements of $^{160}$Dy($p,γ$)$^{161}$Ho and $^{161}$Dy($p,n$)$^{161}$Ho in the beam energy range of 3.4 - 7.0 MeV, partially covering the Gamow window. Such determinations ar…
In supernova cores and neutron star crusts, nuclei with exotic shapes such as rod-like and slab-like nuclei are expected to exist. These nuclei are collectively called nuclear "pasta". For the past decades, existence of the pasta phases in the equilibrium state has been studied using various methods. Recently, the formation process of the pasta phases, which has been a long-standing problem, has been unveiled using molecular dynamics simulations. In this review, we first provide the astrophysical background of supernovae and neutron stars and overview the history of the study of the pasta phas…
Understanding the origin of the elements has been a decades long pursuit, with many open questions still remaining. Old stars found in the Milky Way and its dwarf satellite galaxies can provide answers because they preserve clean elemental patterns of the nucleosynthesis processes that operated some 13 billion years ago. This enables the reconstruction of the chemical evolution of the elements. Here we focus on the astrophysical signatures of heavy neutron-capture elements made in the s-, i- and r-process found in old stars. A highlight is the recently discovered r-process galaxy Reticulum II …
Exotic nuclei, particularly those near the driplines, are at the core of one of the fundamental questions driving nuclear structure and astrophysics today: what are the limits of nuclear binding? Exotic nuclei play a critical role in both informing theoretical models as well as in our understanding of the origin of the heavy elements. Our purpose is to refine existing mass models through the training of an artificial neural network that will mitigate the large model discrepancies far away from stability. The basic paradigm of our two-pronged approach is an existing mass model that captures as …
Fundamental differences in the prediction of reaction rates with intermediate and heavy target nuclei compared to the ones with light nuclei are discussed, with special emphasis on stellar modifications of the rates. Ground and excited state contributions to the stellar rates are quantified, deriving a linear weighting of excited state contributions despite of a Boltzmann population of the nuclear states. A Coulomb suppression effect of the excited state contributions is identified, acting against the usual Q-value rule in some reactions. The proper inclusion of experimental data in revised st…
Gamma-ray production cross section excitation functions have been measured for $30$, $42$, $54$ and $66$ MeV proton beams accelerated onto targets of astrophysical interest, $^{nat}$C, C + O (Mylar), $^{nat}$Mg, $^{nat}$Si and $^{56}$Fe, at the Sector Separated Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with 8 Compton suppressed HPGe clover detectors was used to record $γ$-ray data. For known, intense $γ$-ray lines the previously reported experimental data measured up to $E_{p}\simeq$ $25$ MeV at the Washington and Orsay tandem accelerators were…
Gamow-Teller (GT) strength transitions are an ideal probe for testing nuclear structure models. In addition to nuclear structure, GT transitions in nuclei directly affect the early phases of Type Ia and Type-II supernovae core collapse since the electron capture rates are partly determined by these GT transitions. In astrophysics, GT transitions provide an important input for model calculations and element formation during the explosive phase of a massive star at the end of its life-time. Recent nucleosynthesis calculations show that odd-odd and odd-A nuclei cause the largest contribution in t…
The determination of astrophysical reaction rates requires different approaches depending on the conditions in hydrostatic and explosive burning. The focus here is on astrophysical reaction rates for radiative neutron capture reactions. Relevant nucleosynthesis processes not only involve the s-process but also the i-, r- and $γ$-processes, which from the nuclear perspective mainly differ in the relative interaction energies of neutrons and nuclei, and in the nuclear level densities of the involved nuclei. Emphasis is put on the difference between reactions at low and high temperature. Possible…
Tabulated rates for astrophysical photodisintegration reactions make use of Boltzmann statistics for the photons involved as well as the interacting nuclei. Here we derive analytic corrections for the Planck-spectrum quantum statistics of the photon energy distribution. These corrections can be deduced directly from the detailed-balance condition without the assumption of equilibrium as long as the photons are represented by a Planck spectrum. Moreover we show that these corrections affect not only the photodisintegration rates but also modify the conditions of nuclear statistical equilibrium …
We calculated the Maxwellian-averaged cross sections (MACS) and astrophysical reaction rates of the stellar nucleosynthesis reactions (n,$γ$), (n,fission), (n,p), (n,$α$) and (n,2n) using the ENDF/B-VII.0-, JEFF-3.1-, JENDL-3.3-, and ENDF/B-VI.8-evaluated nuclear-data libraries. Four major nuclear reaction libraries were processed under the same conditions for Maxwellian temperatures ({\it kT}) ranging from 1 keV to 1 MeV. We compare our current calculations of the {\it s}-process nucleosynthesis nuclei with previous data sets and discuss the differences between them and the implications for n…
