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Recent improvements in stellar models for intermediate-mass stars and massive stars (MSs) are recalled, together with their expectations for the synthesis of radioactive nuclei of lifetimes τ ≲ 25 Myr, in order to re-examine the origins of now extinct radioactivities that were alive in the solar nebula. The Galactic inheritance broadly explains most of them, especially if r-process nuclei are produced by neutron star merging, according to recent models. Instead, 26Al, 41Ca, 135Cs, and possibly 60Fe require nucleosynthetic events close to the solar formation. We outline the persisting difficulties to account for these nuclei by intermediate-mass stars (2 ≲ M/M ☉ ≲ 7-8). Models of their final stages now predict the ubiquitous formation of a 13C reservoir as a neutron capture source; hence, even in the presence of 26Al production from deep mixing or hot bottom burning, the ratio 26Al/107Pd remains incompatible with measured data, with a large excess in 107Pd. This is shown for two recent approaches to deep mixing. Even a late contamination by an MS encounters problems. In fact, the inhomogeneous addition of supernova debris predicts nonmeasured excesses on stable isotopes. Revisions invoking specific low-mass supernovae and/or the sequential contamination of the presolar molecular cloud might be affected by similar problems, although our conclusions here are weakened by our schematic approach to the addition of SN ejecta. The limited parameter space that remains to be explored for solving this puzzle is discussed.

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 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

The exact conditions for the supernova high-entropy wind (HEW) as one of the favored sites for the rapid neutron-capture (r-) process still cannot be reproduced selfconsistently in present hydrodynamic simulations. Therefore, we have performed large-scale network calculations within a parameterized HEW model to constrain the necessary conditions for a full r-process, and to compare our results with recent astronomical observations. A superposition of entropy trajectories with model-inherent weightings results in an excellent reproduction of the overall solar-system isotopic abundances ( N r ,⊙ ) of the “main” r-process elements beyond Sn. For the lighter r-elements, our model supports earlier qualitative ideas about a multiplicity of nucleosynthesis processes in the Fe-group region. In the high-entropy-wind scenario, these suggestions are quantified, and the origin of the “missing” abundances to N r ,⊙ is determined to be a rapid primary charged-particle (α-) process, thus excluding a classical “weak” neutron-capture component. This explains the recent halo-star observations of a non-correlation of Cu–Ge and Sr–Zr with metallicity [Fe/H] and r-process enrichment [Eu/H]. Moreover, for the first time a partial correlation with the “main” r-process is identified for Ru and Pd.

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.

We obtain age estimates for the progenitor(s) of the extremely metal-poor ([Fe/H = -2.9) halo star CS 31082-001, based on the recently reported first observation of a Uranium abundance in this (or any other) star. Age estimates are derived by application of the classical r-process model with updated nuclear physics inputs. The [U/Th] ratio yields an age of 13+-4 Gyr or 8+-4 Gyr, based on the use of the ETFSI-Q or the new HFBCS-1 nuclear mass models, respectively. Implications for Thorium chronometers are discussed.

The use of a resonance ionization laser ion source at CERN/ISOLDE has made it possible to study the decay of very neutron-rich Sn135-137. The decay of Sn-135 is found to populate low-energy levels in Sb-135 via direct beta decay and the first excited state in Sb-134 by beta-delayed neutron emission. The level structure of Sb-135 Will be discussed and a possible signature for a more diffuse nuclear surface considered.

A chemically selective laser ion source has been used in a β-decay study of heavy Ag isotopes into even-even Cd nuclides. Gamma-spectroscopic techniques in time-resolving event-by-event and multiscaling modes have permitted the identification of the first 2+ and 4+ levels in 126Cd78, 128Cd80, and tentatively the 2+ state in 130Cd82. From a comparison of these new states in 48Cd with the E(2+) and E(4+)/E(2+) level systematics of 46Pd and 52Te isotopes and several recent model predictions, possible evidence for a weakening of the spherical N = 82 neutron-shell below double-magic 132Sn is obtained.

The use of chemically selective laser ionization combined with beta-delayed neutron counting at CERN/ISOLDE has permitted identification and half-life measurements for 623-ms Mn-61 up through 14-ms Mn-69. The measured half-lives are found to be significantly longer near N=40 than the values calculated with a QRPA shell model using ground-state deformations from the FRDM and ETFSI models. Gamma-ray singles and coincidence spectroscopy has been performed for Mn-64 and Mn-66 decays to levels of Fe-64 and Fe-66, revealing a significant drop in the energy of the first 2+ state in these nuclides that suggests an unanticipated increase in collectivity near N=40., Latex-file with 4 figures, 5 pages, Phys. Rev. Lett., in print

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.

Background: The reaction ${}^{18}$O${(\ensuremath{\alpha},n)}^{21}$Ne is a part of the reaction chains leading to the production of ${}^{19}$F and ${}^{22}$Ne during He burning in low-mass and massive AGB stars, respectively. Additionally, it has been observed as a strong background source in the measurement of other $(\ensuremath{\alpha},n)$ reactions.Purpose: Previously low-energy ${}^{18}$O${(\ensuremath{\alpha},n)}^{21}$Ne cross section data have only been available in a non-peer-reviewed form. An improved measurement of this reaction has been done to both clarify its astrophysical influence as well as to provide background yield data for future $(\ensuremath{\alpha},n)$ experiments.Method: The ${}^{18}$O$(\ensuremath{\alpha},{n}_{(0+1)})$ reaction has been measured with a moderating neutron detector. In addition the $(\ensuremath{\alpha},{n}_{1}\ensuremath{\gamma})$ channel has been measured independently by observation of the characteristic 350.7 keV $\ensuremath{\gamma}$ transition in ${}^{21}$Ne. The reaction cross section at energies above ${E}_{\ensuremath{\alpha}}=1100$ keV was determined by a simultaneous $R$-matrix fit to both channels. The strengths of the two lowest-energy resonances at ${E}_{\ensuremath{\alpha}}=959$ keV and ${E}_{\ensuremath{\alpha}}=1066$ keV were analyzed separately using individual Breit-Wigner fits.Results: The cross section of both reaction channels, ${}^{18}$O${(\ensuremath{\alpha},{n}_{0})}^{21}$Ne and ${}^{18}$O${(\ensuremath{\alpha},{n}_{1}\ensuremath{\gamma})}^{21}$Ne, was determined from the threshold energies at 851 keV and 1280 keV, respectively, to 2300 keV. A new reaction rate has been deduced for the temperature range of 0.1 GK to 10 GK. A previously reported resonance at ${E}_{\ensuremath{\alpha}}=888$ keV is explained as background from the contaminant reaction ${}^{17}$O${(\ensuremath{\alpha},n)}^{20}$Ne.Conclusions: In general, our reaction rate is slightly lower than the reaction rates in recent compilations. At temperatures below 0.2 GK the present rate is significantly lower because it could be shown that the lowest reported resonance is background from the reaction ${}^{17}$O${(\ensuremath{\alpha},n)}^{20}$Ne that has been wrongly assigned to ${}^{18}$O${(\ensuremath{\alpha},n)}^{21}$Ne.

Background: The ratio between the rates of the reactions ${}^{17}$O${(\ensuremath{\alpha},n)}^{20}$Ne and ${}^{17}$O${(\ensuremath{\alpha},\ensuremath{\gamma})}^{21}$Ne determines whether ${}^{16}$O is an efficient neutron poison for the $s$ process in massive stars, or if most of the neutrons captured by ${}^{16}$O$(n,\ensuremath{\gamma})$ are recycled into the stellar environment. This ratio is of particular relevance to constrain the $s$ process yields of fast rotating massive stars at low metallicity.Purpose: Recent results on the $(\ensuremath{\alpha},\ensuremath{\gamma})$ channel have made it necessary to measure the $(\ensuremath{\alpha},n)$ reaction more precisely and investigate the effect of the new data on $s$ process nucleosynthesis in massive stars.Method: The ${}^{17}$O$(\ensuremath{\alpha},{n}_{(0+1)})$ reaction has been measured with a moderating neutron detector. In addition, the $(\ensuremath{\alpha},{n}_{1})$ channel has been measured independently by observation of the characteristic 1633 keV $\ensuremath{\gamma}$ transition in ${}^{20}$Ne. The reaction cross section was determined with a simultaneous R-matrix fit to both channels. $(\ensuremath{\alpha},n)$ and $(\ensuremath{\alpha},\ensuremath{\gamma})$ resonance strengths of states lying below the covered energy range were estimated using their known properties from the literature.Result: The reaction channels ${}^{17}$O${(\ensuremath{\alpha},{n}_{0})}^{20}$Ne and ${}^{17}$O${(\ensuremath{\alpha},{n}_{1}\ensuremath{\gamma})}^{20}$Ne were measured in the energy range ${E}_{\ensuremath{\alpha}}=800$ keV to 2300 keV. A new ${}^{17}$O$(\ensuremath{\alpha},n)$ reaction rate was deduced for the temperature range 0.1 GK to 10 GK. At typical He burning temperatures, the combination of the new $(\ensuremath{\alpha},n)$ rate with a previously measured $(\ensuremath{\alpha},\ensuremath{\gamma})$ rate gives approximately the same ratio as current compilations. The influence on the nucleosynthesis of the $s$ process in massive stars at low metallicity is discussed.Conclusions: It was found that in He burning conditions the $(\ensuremath{\alpha},\ensuremath{\gamma})$ channel is strong enough to compete with the neutron channel. This leads to a less efficient neutron recycling compared to a previous suggestion of a very weak $(\ensuremath{\alpha},\ensuremath{\gamma})$ channel. $S$ process calculations using our rates confirm that massive rotating stars do play a significant role in the production of elements up to Sr, but they strongly reduce the $s$ process contribution to heavier elements.

( α , n ) reactions are possible neutron sources for nucleosynthesis processes in stars. At the Nuclear Science Laboratory (NSL) of the University of Notre Dame a neutron detector based on 3He counters embedded in a polyethylene matrix was built to experimentally investigate this type of reactions. Monte Carlo simulations were used to guide the design of the detector used in the experiments. The efficiency of the final detector was experimentally determined and compared to simulations. The detector will be used in future measurements in a next-generation underground laboratory for nuclear astrophysics.

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.

The ratio of the reaction rates of the competing channels 17O(αγ)21Ne and 17O(α,n)20Ne determines the efficiency of 16O as a neutron poison in the s process in low metallicity rotating stars. It has a large impact on the element production, either producing elements to the mass range of A=90 in case of a significant poisoning effect or extending the mass range up to the region of A=150 if the γ channel is of negligible strength. We present an improved study of the reaction 17O(α,n)20Ne, including an independent measurement of the 17O(α,n1)20Ne channel. A simultaneous R-Matrix fit to both the n0 and the n1 channels has been performed. New reaction rates, including recent data on the 17O(α,γ)21Ne reaction, have been calculated and used as input for stellar network calculations and their impact on the s process in rotating massive stars is discussed.

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.

We report the first confirmation of the predicted inversion between the pi2p3/2 and pi1f5/2 nuclear states in the nu(g)9/2 midshell. This was achieved at the ISOLDE facility, by using a combination of in-source laser spectroscopy and collinear laser spectroscopy on the ground states of 71,73,75Cu, which measured the nuclear spin and magnetic moments. The obtained values are mu(71Cu)=+2.2747(8)mu(N), mu(73Cu)=+1.7426(8)mu(N), and mu(75Cu)=+1.0062(13)mu(N) corresponding to spins I=3/2 for 71,73Cu and I=5/2 for 75Cu. The results are in fair agreement with large-scale shell-model calculations.

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.

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.

At the time neon burning is activated in massive stars, large amounts of 25Mg and 26Mg have been accumulated from the previous evolutionary phases. In particular, at typical temperatures for neon shell burning, the reactions 25Mg(α,n)28Si and 26Mg(α,n)29Si become efficient providing additional neutron fluxes and affecting the nucleosynthesis distribution. Good knowledge of the reaction rates is required to study their effect on nucleosynthesis during neon shell burning conditions (T9≳1.5, where T9 is the temperature in gigakelvin). At the Nuclear Science Laboratory, University of Notre Dame, IN, USA we developed a neutron detector to investigate the 25Mg(α,n)28Si and 26Mg(α,n)29Si reactions as possible neutron sources during neon shell burning. In the present paper we briefly describe the experimental procedures developed to measure those reactions. Finally, we discuss the impact of 25Mg(α,n)28Si and 26Mg(α,n)29Si on the s‐process nucleosynthesis for the barium isotopes.

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.

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.

4 pages, 3 figures, 1 table.-- PACS nrs.: 21.10.Tg; 23.40.−s; 27.40.+z., The Advanced-Time-Delayed method was used to measure lifetimes of the states in Ar-41 populated in the β decay of Cl-41. The nuclei Cl-41 were produced at ISOLDE by 1.4-GeV proton bombardment of a thick UCx target and mass-separated as molecular ions, XeCl+. Our measured half-life of the 167.1-keV state, T(1/2) = 315(15) ps, is significantly lower than the previously measured value of 410(30) ps. We have also determined T(1/2) = 260(80) ps and T(1/2) ≤ 46 ps for the 515.9- and 1867.7-keV states, respectively. These are the shortest lifetimes measured so far with the ultrafast timing method using the new LaBr3(Ce) crystals for γ-ray detection., This work was performed as part of an undergraduate research project (ERW) at the Physics Department of the University of Notre Dame. Fast-timing detectors and electronics were provided by the Fast Timing Pool of Electronics. This study was supported in part by the NSF PHY04-57120, Swedish Research Council, BMBF Grant No. 06KY205I, the Alexander von Humboldt Foundation (WBW), Foundation for Polish Science (AK), the European Union Sixth Framework through RII3-EURONS (Contract No. 506065), and the EURTD project TARGISOL (HPRI-CT-2001-50033).

{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 N 28 shell closure has been investigated via the 46 Ar d;p 47 Ar transfer reaction in inverse kinematics. Energies and spectroscopic factors of the neutron p 3 = 2 , p 1 = 2 , and f 5 = 2 states in 47 Ar were determined and compared to those of the 49 Ca isotone. We deduced a reduction of the N 28 gap by 330(90) keV and spin-orbit weakenings of ’ 10 2 and 45(10)% for the f and p states, respectively. Such large variations for the f and p spin-orbit splittings could be accounted for by the proton-neutron tensor force and by the density dependence of the spin-orbit interaction, respectively. This contrasts with the picture of the spin-orbit interaction as a surface term only ispartof: Physical Review Letters vol:97 issue:9 ispartof: location:United States status: published

The \ensuremath{\beta} decay of $^{135}\mathrm{Sn}$ was studied at CERN/ISOLDE using a resonance ionization laser ion source and mass separator to achieve elemental and mass selectivity, respectively. \ensuremath{\gamma}-ray singles and $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidence spectra were collected as a function of time with the laser on and with the laser off. These data were used to establish the positions of new levels in $^{135}\mathrm{Sb}$, including new low-spin states at 440 and 798 keV, which are given tentative spin and parity assignments of $3/{2}^{+}$ and $9/{2}^{+}$, respectively. The observed levels of $^{135}\mathrm{Sb}$ are compared with shell-model calculations using different single-particle energies and different interactions.

The level structure of odd-odd $^{134}\mathrm{Sb}$ has been studied at CERN/ISOLDE following the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{134}\mathrm{Sn}$ and the \ensuremath{\beta}-delayed neutron decay of $^{135}\mathrm{Sn}$. Elemental and isobaric separation were accomplished by use of a resonance ionization laser ion source and an on-line mass separator, respectively. Both \ensuremath{\gamma}-ray singles and $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence data were taken as a function of time. New levels at 279, 441, 555, 617, and 1385 keV have been identified and given proposed spin and parity assignments of ${7}^{\ensuremath{-}}$, ${5}^{\ensuremath{-}}$, ${6}^{\ensuremath{-}}$, ${4}^{\ensuremath{-}}$, and ${5}^{\ensuremath{-}}$, respectively, following \ensuremath{\beta}-delayed neutron decay of $7/{2}^{\ensuremath{-}}$ $^{135}\mathrm{Sn}$. New ${1}^{\ensuremath{-}}$ levels have been identified at 1900, 2170, and 2430 keV following the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of ${0}^{+}$ $^{134}\mathrm{Sn}$. The resulting level structures are compared to shell-model calculations using the CD Bonn interaction and scaled and unscaled Kuo-Herling interactions developed for the $^{208}\mathrm{Pb}$ region. Remarkably enough, the unscaled Kuo-Herling interaction provides the best fit for the levels below 1 MeV.

Results from a panel discussion on Data Dissemination (Nuclear Data Web Sites and Publications, Nuclear Astrophysics) and International Collaborations (NRDC, NSDD, and WPEC) are presented. Challenges and exciting new developments in these areas are 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.

A pure neutron-rich {sup 26}Ne beam was obtained at the ISOLDE facility using isobaric selectivity. This was achieved by a combination of a plasma ion source with a cooled transfer line and subsequent mass separation. The high quality of the beam and good statistics allowed us to obtain new experimental information on the {sup 26}Ne {beta}-decay properties and resolve a contradiction between earlier experimental data and prediction of shell-model calculations.

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 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