The production of about half of the heavy elements found in nature is assigned to a specific astrophysical nucleosynthesis process: the rapid neutron-capture process ($r$ process). Although this idea was postulated more than six decades ago, the full understanding faces two types of uncertainties or open questions: (a) The nucleosynthesis path in the nuclear chart runs close to the neutron-drip line, where presently only limited experimental information is available, and one has to rely strongly on theoretical predictions for nuclear properties. (b) While for many years the occurrence of the $r$ process has been associated with supernovae, where the innermost ejecta close to the central neutron star were supposed to be neutron rich, more recent studies have cast substantial doubts on this environment. Possibly only a weak $r$ process, with no or negligible production of the third $r$-process peak, can be accounted for, while much more neutron-rich conditions, including an $r$-process path with fission cycling, are likely responsible for the majority of the heavy $r$-process elements. Such conditions could result during the ejection of initially highly neutron-rich matter, as found in neutron stars, or during the fast ejection of matter that has previously experienced strong electron captures at high densities. Possible scenarios are the mergers of neutron stars, neutron-star–black hole mergers, but also include rare classes of supernovae as well as hypernovae or collapsars with polar jet ejecta, and possibly also accretion disk outflows related to the collapse of fast rotating massive stars. The composition of the ejecta from each event determines the temporal evolution of the $r$-process abundances during the “chemical” evolution of the Galaxy. Stellar $r$-process abundance observations have provided insight into and constraints on the frequency of and conditions in the responsible stellar production sites. One of them, neutron-star mergers, was just identified thanks to the observation of the $r$-process kilonova electromagnetic transient following the gravitational wave event GW170817. These observations, which are becoming increasingly precise due to improved experimental atomic data and high-resolution observations, have been particularly important in defining the heavy element abundance patterns of the old halo stars, and thus in determining the extent and nature of the earliest nucleosynthesis in the Galaxy. Combining new results and important breakthroughs in the related nuclear, atomic, and astronomical fields of science, this review attempts to answer the question “How were the elements from iron to uranium made?”

The ${}^{13}\mathrm{C}({}^4\mathrm{He},4\alpha )n$ breakup reaction has been studied at beam energies of 27.0, 27.5, and 28.0 MeV. A comparison with previous measurements of the ${}^{12}\mathrm{C}({}^4\mathrm{He},{}^8\mathrm{Be}){}^8\mathrm{Be}$ excitation function and ${}^{12}\mathrm{C}({}^{16}\mathrm{O},4\alpha ){}^{12}\mathrm{C}$ breakup channel suggests the ${}^8\mathrm{Be}_{\mathrm{gs}}+{}^8\mathrm{Be}_{\mathrm{gs}}$ decay of ${}^{16}\mathrm{O}$ is observed from a possible $2^{+}$ state at $17.3\pm 0.2$ MeV, a $4^{+}$ state at $18.0\pm 0.2$ MeV, a $2^{+}$ or $4^{+}$ state at $19.4\pm 0.2$ MeV, and a $4^{+}$ or $6^{+}$ state at $21.0\pm 0.2$ MeV. The $2^{+}$ or $4^{+}$ assignment for the ($19.4\pm 0.2$)-MeV state appears to be supported by the relative cross sections expected for resonant and sequential breakup reactions.

The CNO cycle is the main energy source in massive stars during their hydrogen burning phase, and, for our sun, it contributes at the $\approx 1\%$ level. As the ${}^{14}\mathrm{N}(p,\gamma ){}^{15}\mathrm{O}$ reaction is the slowest in the cycle, it determines the CNO energy production rate and thus the CNO contribution to the solar neutrino flux. These CNO neutrinos are produced primarily from the $\beta$ decay of ${}^{15}\mathrm{O}$ and, to a lesser extent, from the decay of ${}^{13}\mathrm{N}$. Solar CNO neutrinos are challenging to detect, but they can provide independent new information on the metallicity of the solar core. Recently, CNO neutrinos from ${}^{15}\mathrm{O}$ have been identified for the first time with the Borexino neutrino detector at the INFN Gran Sasso underground laboratory. There are, however, still some considerable uncertainties in the ${}^{14}\mathrm{N}(p,\gamma ){}^{15}\mathrm{O}$ reaction rate under solar temperature conditions. The low energy reaction data presented here, measured at the CASPAR underground accelerator, aim at connecting existing measurements at higher energies and attempts to shed light on the discrepancies between the various data sets, while moving towards a better understanding of the ${}^{14}\mathrm{N}(p,\gamma ){}^{15}\mathrm{O}$ reaction cross section. The present measurements span proton energies between 0.27 and 1.07 MeV, closing a critical gap in the existing data. A multichannel $R$-matrix analysis was performed with the entire new and existing data sets and is used to extrapolate the astrophysical $S$ factors of the ground state and the 6.79 MeV transition to low energies. The extrapolations are found to be in agreement with previous work, but find that the discrepancies between measured data and $R$-matrix fits, both past and present, still exist. We examine the possible reasons for these discrepancies and thereby provide recommendations for future studies.

Background: The nature of low-lying oscillations or excitations around the equilibrium deformed nuclear shape remains an open question in a nuclear structure. The question revolves around the possible degrees of freedom in deformed nuclei. Rotational motion is an expected feature of deformed nuclei; the open challenge is whether the “granularity” of the nuclei allows single or multiple quanta of vibrational oscillations or excitations superimposed on the equilibrium deformed shape of the nucleus. Special emphasis is placed on the $K^{\pi }=0^{+},\beta$ vibration whose existence is open to debate some 40 years after Bohr-Mottelson-Rainwater's Nobel prize for connecting nucleon motion to the emergence of collectivity.