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This article addresses three of the four nucleosynthesis processes involved in producing heavy nuclei beyond Fe (with a main focus on the r -process). Opposite to the fourth process (the s -process), which operates in stellar evolution during He- and C-burning, they are all related to explosive burning phases, (presumably) linked to core collapse supernova events of massive stars. The (classical) p -process is identified with explosive Ne/O-burning in outer zones of the progenitor star. It is initiated by the passage of the supernova shock wave and acts via photodisintegration reactions like a spallation process which produces neighboring (proton-rich) isotopes from pre-existing heavy nuclei. The reproduction of some of the so-called lighter p -isotopes with A 100 faces problems in this environment. The only recently discovered ν p -process is related to the innermost ejecta, the neutrino wind expelled from the hot proto-neutron star after core collapse and the supernova explosion. This neutrino wind is proton-rich in its early phase, producing nuclei up to 64Ge. Reactions with neutrinos permit to overcome decay/reaction bottlenecks for the flow beyond 64Ge, thus producing light p -isotopes, which face problems in the classical p -process scenario. The understanding of the r -process, being identified for a long time with rapid neutron captures and passing through nuclei far from stability, is still experiencing major problems. These are on the one hand related to nuclear uncertainties far from stability (masses, half-lives, fission barriers), affecting the process speed and abundance peaks. On the other hand the site is still not definitely located, yet. (i) Later, possibly neutron-rich, high entropy phases of the neutrino wind (if they materialize!) could permit its operation. (ii) Other options include the ejection of very neutron-rich neutron star-like matter, occurring possibly in neutron star mergers or core collapse supernova events with jets, related to prior stellar evolution with high rotation rates and magnetic fields. Two different environments are required for a weak and a main/strong r -process, witnessed by observations of low metallicity stars and meteoritic inclusions, which could possibly be identified with the two options listed above, i.e. the weak r -process could be related to the neutrino wind when changing from p -rich to n -rich conditions.

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 relative abundances of the radionuclides 129 I and 182 Hf in the Early Solar System (ESS) in conjunction with observations on extremely metal-poor stars have been interpreted as evidence for two distinct types (L and H events) of the r-process. In particular, it has been postulated that iodine is produced exclusively during L events, while barium and elements above are produced by H events only. In this context we explore predictions from the high entropy wind (HEW) model for the r-process. Within this scenario, the full expected entropy range produces abundances which are inconsistent with these postulates. Only by excluding the entropy range below a precisely defined value can Ba and elements above be produced without significant contributions to iodine. Achieving the required clear “cut” at always the exactly same entropy value would be remarkable; the cut may have been a characteristic of the last r-process contribution, however. Alternative explanations for a relative overabundance of 182 Hf and/or a deficit of 129 I in the Early Solar System include a late neutron burst contribution to 182 Hf and a 129 I deficit due to the volatile nature of the element iodine.

Observed neutron-capture elemental abundances in metal-poor stars, along with ongoing analysis of the extremely metal-poor Eu-enriched sub-class provide new guidance for astrophysical models aimed at finding the r-process sites. The present paper emphasizes the importance of nuclear physics parameters entering in these models, particularly β -decay properties of neutron-rich nuclei. In this context, several r-process motivated β -decay experiments performed at the National Superconducting Cyclotron Laboratory (NSCL) are presented, including a summary of results and impact on model calculations.

Nucleosynthesis theory predicts that half of the chemical elements above Fe are formed in explosive stellar scenarios by the r-process. A correct modelling of this process requires knowledge of nuclear properties very far from stability and a detailed description of the astrophysical environments. Using updated experimental and theoretical nuclear-physics data, we have performed detailed r-process calculations within the classical, site-independent “waiting-point” approximation and the “neutrino-wind” scenario of core-collapse type II supernovae (SNII). Nuclear and astrophysical constraints on the reproduction of the available r-process observables will be reviewed.

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.

A correct understanding of r-process nucleosynthesis requires the knowledge of nuclear-structure properties far from β-stability and a detailed description of the possible astrophysical environments. With respect to nuclear data, in recent years the main focus at CERN/ISOLDE has been put on the 132Sn region to explore the role of the N=82 shell closure and its consequences on the r-process matter flow through the A ≃ 130 Solar-System r-abundance peak.

Within a full dynamical parameter study including freezeout effects, we have determined the astrophysical conditions for an r-process in the so-called ``neutrino-wind`` scenario of core-collapse type II supernovae (SNII). We have started our calculations after the total photo disintegration of the matter above the nascent neutron star at 9 (.) 101 Kelvin with protons and neutrons. We have used the charged-particle network of Thielemann and the r-process code of Freiburghaus, combined with the NON-SMOKER neutron-capture rates of Rauscher, nuclear masses from the ETFS1-Q mass model and recent experimental and theoretical gross beta-decay properties. Using the three parameters V-exp (expansion speed of the shock wave), S (entropy of the bubble) and the neutron-to-proton ratio Y-e, we show that the above quantities have to fulfill specific conditions in order to make a successful r-process. According to observations and hydrodynamical simulations, respectively, a realistic value for Vexp is 7500 km/s, and Y>0.5.

Background: Nuclear structure plays a significant role on the rapid neutron capture process ($r$ process) since shapes evolve with the emergence of shells and subshells. There was some indication in neighboring nuclei that we might find examples of a new $N=56$ subshell, which may give rise to a doubly magic ${}_{34}^{90}$Se${}_{56}$ nucleus.Purpose: $\ensuremath{\beta}$-decay half-lives of nuclei around ${}^{90}$Se have been measured to determine if this nucleus has in fact a doubly magic character.Method: The fragmentation of a ${}^{136}$Xe beam at the National Superconducting Cyclotron Laboratory at Michigan State University was used to create a cocktail of nuclei in the $A=90$ region.Results: We have measured the half-lives of 22 nuclei near the $r$-process path in the $A=90$ region. The half-lives of ${}^{88}\phantom{\rule{-0.16em}{0ex}}$As and ${}^{90}$Se have been measured for the first time. The values were compared with theoretical predictions in the search for nuclear-deformation signatures of a $N=56$ subshell, and its possible role in the emergence of a potential doubly magic ${}^{90}$Se. The impact of such hypothesis on the synthesis of heavy nuclei, particularly in the production of Sr, Y, and Zr elements was investigated with a weak $r$-process network.Conclusions: The new half-lives agree with results obtained from a standard global QRPA model used in $r$-process calculations, indicating that ${}^{90}$Se has a quadrupole shape incompatible with a closed $N=56$ subshell in this region. The impact of the measured ${}^{90}$Se half-life in comparison with a former theoretical predication associated with a spherical half-life on the weak $r$ process is shown to be strong.

Half-life (${T}_{1/2}$) and \ensuremath{\beta}-delayed neutron branching (${P}_{n}$) values of 492(25) ms and 49(8)$%$, 350(15) ms and 72(8)$%$, and 93(13) ms and 90(10)$%$ for the $r$-process nuclei ${}^{137,138,139}$Sb, respectively, have been measured at the CERN On-Line Isotope Mass Separator (ISOLDE) facility by counting \ensuremath{\beta}-delayed neutrons. More precise ${T}_{1/2}$ and ${P}_{n}$ values of 300(15) ms and 27(4)$%$, and 273(7) ms and 50(8)$%$ for ${}^{136,137}$Sn, respectively, have also been measured. The sources were prepared by using the selective ionization of Sb or Sn with the Resonance Ionization Laser Ion Source and the high-resolution mass separator. The new data for Sb isotopes are compared with calculated ${T}_{1/2}$ and ${P}_{n}$ values for both spherical and nonspherical shapes. The data have been incorporated into parametrized nucleosynthesis calculations of the $r$ process in high-entropy winds of core-collapse supernovae in order to study the properties of the $A$ $=$ 130 solar-system $r$-process abundance peak.

The {beta} decays of very neutron-rich nuclides in the Co-Zn region were studied experimentally at the National Superconducting Cyclotron Laboratory using the NSCL {beta}-counting station in conjunction with the neutron detector NERO. We measured the branchings for {beta}-delayed neutron emission (P{sub n} values) for {sup 74}Co (18{+-}15%) and {sup 75-77}Ni (10{+-}2.8%, 14{+-}3.6%, and 30{+-}24%, respectively) for the first time, and remeasured the P{sub n} values of {sup 77-79}Cu, {sup 79,81}Zn, and {sup 82}Ga. For {sup 77-79}Cu and for {sup 81}Zn we obtain significantly larger P{sub n} values compared to previous work. While the new half-lives for the Ni isotopes from this experiment had been reported before, we present here in addition the first half-life measurements of {sup 75}Co (30{+-}11 ms) and {sup 80}Cu (170{sub -50}{sup +110} ms). Our results are compared with theoretical predictions, and their impact on various types of models for the astrophysical rapid neutron-capture process (r-process) is explored. We find that with our new data, the classical r-process model is better able to reproduce the A=78-80 abundance pattern inferred from the solar abundances. The new data also influence r-process models based on the neutrino-driven high-entropy winds in core collapse supernovae.

Measurements of $\ensuremath{\beta}$-decay properties of $A\ensuremath{\lesssim}110$ r-process nuclei have been completed at the National Superconducting Cyclotron Laboratory at Michigan State University. $\ensuremath{\beta}$-decay half-lives for $^{105}\mathrm{Y}$, $^{106,107}\mathrm{Zr}$, and $^{111}\mathrm{Mo}$, along with $\ensuremath{\beta}$-delayed neutron emission probabilities of $^{104}\mathrm{Y}$, $^{109,110}\mathrm{Mo}$ and upper limits for $^{105}\mathrm{Y}$, $^{103\ensuremath{-}107}\mathrm{Zr}$, and $^{108,111}\mathrm{Mo}$ have been measured for the first time. Studies on the basis of the quasi-random-phase approximation are used to analyze the ground-state deformation of these nuclei.

Since the historical papers by Burbidge et al. and Cameron 50 years ago, it is generally accepted that half of the chemical elements above Fe are formed in explosive stellar scenarios by a rapid neutron‐capture process (the classical “r‐process”). Already from their essential ideas, it became clear that a correct modelling of this nucleosynthesis process requires both, the knowledge of various nuclear properties very far from stability and a detailed description of the astrophysical environments. However, it took about three decades, until in 1986 the first experimental nuclear‐physics data on the neutron‐magic r‐isotopes 80Zn and 130Cd could be obtained, which act as key “waiting points” in the respective A≃80 and 130 peaks of the Solar‐System (SS) r‐abundances (Nr,⊙). Since then, using steadily improved nuclear data, we have optimized our r‐process calculations to reproduce the present observables of the isotopic Nr,⊙ “residuals”, as well as the more recent elemental abundances in ultra‐metal‐poor, r‐process‐enriched halo stars. Concerning the latter observations, we support the basic idea about two different types of r‐processes. Based on our many years' experience with the site‐independent “waiting‐point approach”, we recently have extended our studies to fully dynamical network calculations for the most likely astrophysical r‐process scenario, i.e. the high‐entropy wind (HEW) of core‐collapse type II supernovae (SN II). Again, an excellent reproduction of all observables for the “main” r‐process has been achieved. However, a major difference is the nucleosynthesis origin of the lighter heavy elements in the 29⩽Z⩽45 mass region. Here, the HEW model predicts—instead of a “weak” neutron‐capture r‐process component—a primary rapid charged‐particle process. This may explain the recent observations of a non‐correlation of these elements with the heavier “main” r‐process elements.

In an attempt to constrain the astrophysical conditions for the nucleosynthesis of the classical r‐process elements beyond Fe, we have performed large‐scale dynamical network calculations within the model of an adiabatically expanding high‐ entropy wind (HEW) of type II supernovae (SN II). A superposition of several entropy‐components (S) with model‐inherent weightings results in an excellent reproduction of the overall Solar System (SS) isotopic r‐process residuals (Nr,⊙), as well as the more recent observations of elemental abundances of metal‐poor, r‐process rich halo stars in the early Galaxy. For the heavy r‐process elements beyond Sn, our HEW model predicts a robust abundance pattern up to the Th, U r‐chronometer region. For the lighter neutron‐capture region, an S‐dependent superposition of (i) a normal α‐component directly producing stable nuclei, including s‐only isotopes, and (ii) a component from a neutron‐rich α‐freezeout followed by the rapid recapture of β‐delayed neutrons (βdnrpar; emitted ...

The exact conditions for the supemova high‐entropy wind (HEW) as one of the favored sites for the rapid neutron‐capture (r‐) process still cannot be reproduced self‐consistently in present hydrodynamic astrophysical models. Therefore, we have performed large‐scale dynamical network calculations within a parameterized HEW model to constrain the necessary conditions for a full r‐process and to compare our results with recent observations. A model‐inherently weighted superposition of entropy trajectories results in an excellent reproduction of the overall Solar‐System isotopic abundances (Nr,⊙) of the “main” r‐process elements beyond Sn. For the lighter r‐elements in the range 26⩽Z⩽42, our HEW model supports earlier qualitative ideas about a multiplicity of nucleosynthetic processes leading to the total Nr,⊙ distribution. In the HEW scenario, these suggestions are quantified, and the origin of the missing primary process is confirmed to be a rapid charged‐particle process, thus excluding a “weak” neutron‐capture component. This explains the recent halo‐star observations of a Z‐dependent non‐correlation, respectively partial correlation of the lighter r‐elements with metallicity and/or enrichment of “main” r‐process elements.The exact conditions for the supemova high‐entropy wind (HEW) as one of the favored sites for the rapid neutron‐capture (r‐) process still cannot be reproduced self‐consistently in present hydrodynamic astrophysical models. Therefore, we have performed large‐scale dynamical network calculations within a parameterized HEW model to constrain the necessary conditions for a full r‐process and to compare our results with recent observations. A model‐inherently weighted superposition of entropy trajectories results in an excellent reproduction of the overall Solar‐System isotopic abundances (Nr,⊙) of the “main” r‐process elements beyond Sn. For the lighter r‐elements in the range 26⩽Z⩽42, our HEW model supports earlier qualitative ideas about a multiplicity of nucleosynthetic processes leading to the total Nr,⊙ distribution. In the HEW scenario, these suggestions are quantified, and the origin of the missing primary process is confirmed to be a rapid charged‐particle process, thus excluding a “weak” neutron‐cap...

Nucleosynthesis is the science related to all astrophysical processes which are responsible for the abundances of the elements and their isotopes in the universe. The astrophysical sites are the big bang and stellar objects. The working of nucleosynthesis processes is presented in a survey of events which act as abundance sources. For intermediate-mass and heavy elements, these are stellar evolution, type Ia and core collapse supernovae as well as hypernovae. We discuss successes and failures of existing processes and possible solutions via new (hitherto unknown) processes. Finally an analysis of their role is given in the puzzle to explain the evolution of the elemental and isotopic compositions found in galaxies, and especially the mixture found in the solar system. Different timescales due to the progenitor mass dependence of the endpoints of stellar evolution (type II supernova explosions — SNe II vs. planetary nebulae) or single vs. binary stellar systems (the latter being responsible for novae, type Ia supernovae — SNe Ia, or X-ray bursts) are the keys to understand galactic evolution. At very early times, the role of explosion energies of events, polluting pristine matter with a composition originating only from the big bang, might also play a role. We also speculate on the role of very massive stars not undergoing SN II explosions but rather causing “hypernovae” after the formation of a central black hole via core collapse.

Observations of metal‐poor stars in the last decade have revealed an abundance pattern that have recently been explained as the result of two nucleosynthesis processes, a strong r‐process that creates most of the Z⩾56 and some 38⩽Z⩽47 abundances and a light element primary process (LEPP) responsible for creating the remaining 38⩽Z⩽47 abundances and some small contribution to heavier elements. We review some of the current literature on the LEPP and show a derived abundance pattern as a function of mass number.

{beta}-delayed neutron emission branchings (or upper limits) for neutron rich {sup 116-120}Rh, {sup 120-122}Pd, and {sup 124}Ag have been measured. These branching ratios serve as direct inputs to astrophysical rapid neutron capture process models and affect the final abundances calculated in these models. In addition, half-lives for neutron rich {sup 114-115}Tc, {sup 114-118}Ru, {sup 116-121}Rh, and {sup 119-124}Pd near the proposed path of the r-process have also been measured. The results agree with theoretical quasiparticle random-phase approximation calculations within model uncertainties; the only exception is the delayed neutron branching in the decay of {sup 120}Rh, which is found to be much smaller than predicted.

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.

This introductory review aims at understanding r-process nucleosynthesis by addressing the issues involved, nuclear properties, necessary environment conditions, properties of different suggested r-process sites, observational constraints and Galactic evolution. We summarize the remaining challenges and uncertainties which need to be overcome for a full understanding of the nature and site(s) of the r-process.

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

The present paper aims at understanding r-process nucleosynthesis by addressing the nuclear physics involved, the necessary environment conditions in the (stellar) production sites, and the observational constraints. We also summarize the remaining challenges and uncertainties which need to be overcome for a full understanding of the nature of the r-process.

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

Beta‐decay half‐lives and β‐delayed neutron‐emission probabilities of the very neutron‐rich nuclei 43P, 42,44,45S and 44‐46Cl, 47Ar have been recently measured. These isotopes, which lie at or close to the N=28 magic shell were produced at GANIL in interactions of a 60 MeV/u 48Ca beam with a 64Ni target, and were separated by the doubly achromatic spectrometer LISE3. Their decay was studied by a β or β‐n time correlation measurement. The results are compared to recent model predictions and indicate a rapid weakening of the N=28 shell below 4820Ca28. The nuclear structure effects reflected in the decay properties of the exotic S and Cl isotopes may be the clue for the astrophysical understanding of the unusual 48Ca/46Ca abundance ratio measured in the solar system, or observed in EK‐inclusions of the Allende meteorite.

The present paper reports on several r-process motivated β-decay experiments undertaken at the National Superconducting Cyclotron Laboratory. β-decay half-lives and β-delayed neutron-emission probabilities were measured for nuclei around the r-process A = 70–80 and A = 90 – 110 mass regions. The data are discussed on the basis of quasi-random phase approximation calculations. The emphasis is made on the impact of these data upon calculations of r-process abundances.

Rapid neutron-capture (r-process) nucleosynthesis of heavy elements generally involves the participation of large numbers of stable to highly unstable nuclear species. Most of these properties are experimentally unknown and have to be predicted from nuclear models. So far, the uncertainties of such predictions have not allowed putting substantial constraints on astrophysical scenarios. For the classical r-process it is shown that the s-decay properties of only a few key-nuclei, i.e. the recently measured “waiting-point” nuclei 130Cd82 and 80Zn50 together with new shell-model predictions for their N ≈ 82 and 50 neighbours, may be sufficient to explain the observed r-abundances in the A ≈ 130 and 80 abundance peaks. Based on this result, new constraints are given on the stellar conditions under which a steady-flow r-process has operated.

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.