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The neutron long counter NERO was built at the National Superconducting Cyclotron Laboratory (NSCL), Michigan State University, for measuring β -delayed neutron-emission probabilities. The detector was designed to work in conjunction with a β -delay implantation station, so that β decays and β -delayed neutrons emitted from implanted nuclei can be measured simultaneously. The high efficiency of about 40%, for the range of energies of interest, along with the small background, are crucial for measuring β -delayed neutron emission branchings for neutron-rich r-process nuclei produced as low intensity fragmentation beams in in-flight separator facilities.

The astrophysical site of the r-process is still uncertain, and a full exploration of the systematics of this process in terms of its dependence on nuclear properties from stability to the neutron drip-line within realistic stellar environments has still to be undertaken. Sufficiently high neutron to seed ratios can only be obtained either in very neutron-rich low-entropy environments or moderately neutron-rich high-entropy environments, related to neutron star mergers (or jets of neutron star matter) and the high-entropy wind of core-collapse supernova explosions. As chemical evolution models seem to disfavor neutron star mergers, we focus here on high-entropy environments characterized by entropy $S$, electron abundance $Y_e$ and expansion velocity $V_{exp}$. We investigate the termination point of charged-particle reactions, and we define a maximum entropy $S_{final}$ for a given $V_{exp}$ and $Y_e$, beyond which the seed production of heavy elements fails due to the very small matter density. We then investigate whether an r-process subsequent to the charged-particle freeze-out can in principle be understood on the basis of the classical approach, which assumes a chemical equilibrium between neutron captures and photodisintegrations, possibly followed by a $\beta$-flow equilibrium. In particular, we illustrate how long such a chemical equilibrium approximation holds, how the freeze-out from such conditions affects the abundance pattern, and which role the late capture of neutrons originating from $\beta$-delayed neutron emission can play., Comment: 52 pages, 31 figures

Rapid neutron capture in stellar explosions is responsible for the heaviest elements in nature, up to Th , U and beyond. This nucleosynthesis process, the r-process, is unique in the sense that a combination of nuclear physics far from stability (masses, half-lives, neutron-capture and photodisintegration, neutron-induced and beta-delayed fission and last but not least neutrino-nucleus interactions) is intimately linked to ejecta from astrophysical explosions (core collapse supernovae or other neutron star related events). The astrophysics and nuclear physics involved still harbor many uncertainties, either in the extrapolation of nuclear properties far beyond present experimental explorations or in the modeling of multidimensional, general relativistic (neutrino-radiation) hydrodynamics with rotation and possibly required magnetic fields. Observational clues about the working of the r-process are mostly obtained from solar abundances and from the abundance evolution of the heaviest elements as a function of galactic age, as witnessed in old extremely metal-poor stars. They contain information whether the r-process is identical for all stellar events, how abundance features develop with galactic time and whether the frequency of r-process events is comparable to that of average core collapse supernovae - producing oxygen through titanium, as well as iron-group nuclei. The theoretical modeling of the r-process has advanced from simple approaches, where the use of static neutron densities and temperatures can aid to test the influence of nuclear properties far from stability on abundance features, to more realistic expansions with a given entropy, global neutron/proton ratio and expansion timescales, as expected from explosive astrophysical events. The direct modeling in astrophysical events such as supernovae still faces the problem whether the required conditions can be met.

We tabulate the ground-state odd-proton and odd-neutron spins and parities, proton and neutron pairing gaps, one- and two-neutron separation energies, quantities related to β -delayed one- and two-neutron emission probabilities, average energy and average number of emitted neutrons, β -decay energy release and half-life with respect to Gamow–Teller decay with a phenomenological treatment of first-forbidden decays, one- and two-proton separation energies, and α -decay energy release and half-life for 9318 nuclei ranging from 16O to 339136 and extending from the proton drip line to the neutron drip line. This paper is a new and improved version of Atomic Data And Nuclear Data Tables [66 131 (1997)]. The starting point of our present work is the new study (FRDM(2012)) of nuclear ground-state masses and deformations based on the finite-range droplet model and folded-Yukawa single-particle potential published in a previous issue of Atomic Data And Nuclear Data Tables [109–110, 1 (2016)]. The β -delayed neutron-emission probabilities and Gamow–Teller β -decay rates are obtained from a quasi-particle random-phase approximation with single-particle levels and wave functions at the calculated nuclear ground-state shapes as input quantities. A development since 1997 is we now use a Hauser–Feshbach approach to account for (n, γ ) competition and treat first-forbidden decay in a phenomenological approach.

Some neutrons are emitted from fission fragments several seconds to several minutes after fission occurs. These delayed neutrons play a key role for the conduct and in safety aspects of nuclear reactors [1]. But the probabilities to emit such neutrons (Pn) are not well known. A summary of different database and compilation of Pn values is presented to show these discrepancies and uncertainties. Experiments are carried out at the Lohengrin mass spectrometer (at Institut Laue Langevin in Grenoble) and at the ISOLDE facility (CERN) in order to measure some Pn values. Two different techniques are used: either by using gamma‐rays detection or neutron emission detection. These two techniques and some preliminary results are presented.

The $^{44}\mathrm{Ar}$($d,p$)$^{45}\mathrm{Ar}$ neutron transfer reaction was performed at $10A$ MeV. Measured excitation energies, deduced angular momenta, and spectroscopic factors of the states populated in $^{45}\mathrm{Ar}$ are reported. A satisfactory description of these properties is achieved in the shell model framework using a new $\mathit{sdpf}$ interaction. The model analysis is extended to more exotic even-$Z$ nuclei down to ${}_{14}^{41}{\mathrm{Si}}_{27}$ to study how collectivity impacts the low-lying structure of $N=27$ neutron-rich nuclei.

Nucleosynthesis theory predicts that about half of the chemical elements above iron are formed in explosive stellar scenarios by the r‐process, i.e. a combination of rapid neutron captures, inverse photodisintegrations, and slower β‐decays, β‐delayed processes, as well as fission and possibly interactions with neutrinos. A correct modelling of this process, therefore, requires the knowledge of nuclear properties very far from stability and a detailed description of the astrophysical environments. With respect to nuclear data, after an initial period of measuring classical “waiting‐point” nuclei with magic neutron numbers, recent investigations have paid special attention to shape transitions and the erosion of classical shell gaps with possible occurrence of new magic numbers. The status of experimental and theoretical nuclear data on masses and β‐decay properties will be briefly reviewed, and consequences on the overall r‐process matter flow up to the cosmochronometers 232Th and 238U will be discussed.

The production of about half of the heavy elements in nature occurs via the r‐process, i.e., a combination of rapid neutron captures, inverse photodisintegrations, and slower β‐decays, β‐delayed processes as well as fission and possibly interactions with neutrino fluxes. A correct understanding and modelling of this nucleosynthesis process requires the knowledge of nuclear properties far from stability and a detailed description of the astrophysical environments. Experiments at radioactive ion beam facilities have played a pioneering role in exploring the characteristics of nuclear structure in terms of masses and β‐decay properties. Initial examinations paid attention to short‐lived “waiting‐point” nuclei with magic neutron numbers related to the location and height of the solar‐system r‐process abundance peaks, while more recent activities, mainly in the 132Sn region, focus on the evolution of shell effects as a function of isospin. In this context, shape transitions and the erosion of the classical shell gaps with possible occurrence of new magic numbers play an important role. Consequences of improved theoretical and experimental nuclear data on calculations of the r‐process matter flow will be presented, and the applicability of the long‐lived actinides 232Th and 238U as cosmo‐chronometers will be discussed.

Fission is an important process which is responsible not only for the yields of transuranium isotopes, but may have a strong influence on the formation of the majority of heavy nuclei due to fission recycling in the r-process. Calculations of beta-delayed and neutron-induced fission rates were performed taking into account different fission barriers and mass formulae were done. It is shown that an increase of fission barriers results in naturally changes of fission rates, but that the absolute values of fission rates are nevertheless sufficiently high and lead to the termination of the r-process. Furthermore it is discussed, that the probability of triple fission could be high for A < 260 and have an affect on the formation on the heaviest nuclei.

Fission plays an important role in the r-process which is responsible not only for the yields of transuranium isotopes, but may have a strong influence on the formation of the majority of heavy nuclei due to fission recycling. We present calculations of beta-delayed and neutron-induced fission rates, taking into account different fission barriers predictions and mass formulae. It is shown that an increase of fission barriers results naturally in a reduction of fission rates, but that nevertheless fission leads to the termination of the r-process. Furthermore, it is discussed that the probability of triple fission could be high for $A>260$ and have an effect on the formation of the abundances of heavy nuclei. Fission after beta-delayed neutron emission is discussed as well as different aspects of the influence of fission upon r-process calculations., 28 pages, 10 figures, to be published in Nuclear Physics A

Except for 1H, 2H, 3He, 4He, and 7Li, originating from the Big Bang, all heavier elements are made in stellar evolution and stellar explosions. Nuclear physics, and in many cases nuclear structure far from stability, enters in a crucial way. Therefore, we examine in this review the role of nuclear physics in astrophysics in general and in particular how it affects stellar events and the resulting nucleosynthesis. Stellar modeling addresses four major aspects: 1. energy generation and nucleosynthesis, 2. energy transport via conduction, radiation or possibly convection, 3. hydrodynamics/hydrostatics, and finally 4. thermodynamic properties of the matter involved. Nuclear Physics enters via nuclear reaction cross sections and nuclear structure (affecting the composition changes and nuclear energy generation), neutrino-nucleon and neutrino-nucleus cross sections (affecting neutrino opacities and transport), and e.g. the equation of state at and beyond nuclear densities which creates a relation between the nuclear many-body problem and the hydrodynamic response like pressure and entropy. In the following we review these four topics by highlighting the role and impact of nuclear physics in each of these aspects of stellar modeling. The main emphasis is put on the connection to element synthesis., 32 pages, 8 figures, review, to appear in Prog. Nuc. Part. Phys.; layout changed (v2), journal reference corrected (v3)

Progress in the astrophysical understanding of r-process nucleosynthesis also depends on the knowledge of nuclear-physics quantities of extremely neutron-rich isotopes. In this context, experiments at CERN-ISOLDE have played a pioneering role in exploring new shell-structure far from stability. Possible implications of new nuclear-data input on the reproduction of r-abundance observations are presented., 10 pages, 3 figures; Proc. "Nuclei in the Cosmos 2000", Nucl. Phys. A

Neutron-rich Co nuclei with A=66–70 were produced by the laser-ionization isotope-separation on-line method. The β decay from these nuclei has been studied. A case example is given by reporting on the observed decay scheme of 68Co. The half life of the ground-state decay of this nucleus was measured to be 0.21(3) seconds. In addition, a new β decaying isomer half life of 1.16(25) seconds was discovered. The level scheme of 68Ni has been significantly extended, and an interpretation of the observed levels is made by assuming that the N=40 gap has the characteristics of a shell closure.

We report on the first β-γ spectroscopy measurements of the neutron-rich 68–70Co and 70–74Ni nuclei, produced in proton-induced fission of 238U and ionized in a laser ion guide coupled to an on-line mass separator. Several γ lines from the decay of these nuclei have been identified, half-lives determined and production cross sections deduced. The derived level schemes for the copper and nickel isotopes show that the occupation of the ν(1g9/2) state has a strong influence on the structure of these neutron-rich nuclei. This may have a clear impact on the predicted structure and decay properties of doubly-magic 78Ni.

Delayed neutron emission probabilities,P n , have been calculated using usual nuclear statistical model considerations. The influence of the incident parameters on the calculatedP n -values is discussed. The observed systematic deviation from the experimental neutron emission probabilities may be explained by the persistence of nuclear structure effects not contained in a simple statistical model.

A simple correlation based on the gross theory ofβ-decay is derived between the neutron emission probabilitiesPn of delayed neutron precursors, theirβ-decay energies and the neutron binding energies of the daughter nuclei. The correlation is shown to be valid for delayed neutron precursors among the fission products. ThePn-values of several expected but still unidentified neutron precursors are estimated together with their contributions to the delayed neutron groups in thermal-neutron induced fission of235U. Some aspects of theβ-strength function for transitions into highly excited states are discussed.

Neutron-neutron coincidences show that the $\ensuremath{\beta}$ decay of 8.5-ms $^{11}\mathrm{Li}$ is followed by the emission of two neutrons in an intensity of (9\ifmmode\pm\else\textpm\fi{}3)%.

Appropriate Nilsson parameters and deformations for RPA shell model calculations or A≂100 neutron‐rich nuclei are derived. They allow Nilsson orbital assignments even on the basis of gross β‐decay properties. Matching of the A≂100 and A≂150 mass regions yields evidence for a local N=64 subshell. A study of the influence of the pairing strength on quasi‐particle configurations indicates a pairing reduction of only 50–60% at A≂100, in contrast to a recent proposition of total pairing collapse.

Rapid‐neutron‐capture processes in explosive astrophysical environments lead to the production of nuclei far away from β‐stability. It is shown at the examples of solar and meteoritic isotopic anomalies around 48Ca and for the observed r‐abundance peaks at A≂80 and 130, that an understanding of the nucleosynthesis in such environments is intimately related to an understanding of the nuclear‐structure properties of far‐unstable nuclei.

The possible factors responsible for the sudden onset of nuclear deformation in neutron-rich A≅100 nuclei are reviewed from the systematics of subshell occupation numbers for neutron and proton orbitals. The agreement between our results from a Nilsson model with existing selfconsistent HFB calculations strengthens the role of a cumulative neutron-proton interaction, but does not substantiate the conjecture concerning a selective involvement of the πg9/2-νg7/2 spin-orbit-partner orbitals in producing deformation as das suggested in earlier work.

The neutron binding energy in93Sr has been determined to (5230±6) keV from energy correspondences between levels defined by γ-ray transitions and β-delayed neutron emission.