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New half-lives for neutron-rich ruthenium, rhodium and palladium isotopes close to the r-process path along the N=82 closed shell have been measured at the National Superconducting Cyclotron Laboratory at Michigan State University. The studied isotopes are close to the critical A=118-126 mass region in the astrophysical r-process, where incorrect nuclear structure development towards the shell closure may have the most pronounced effect on the abundances of elements produced. Neutron-rich nuclei were produced by fragmentation of a 120-MeV per nucleon 136Xe beam on Be and were separated by the A1900 fragment separator. The nuclei of interest were implanted into a double-sided Si strip detector at the center of the MSU β counting system. Charge states and fully- stripped isotopes were distinguished by a measurement of the total kinetic energy of each implant. Our measured half-lives will provide first clues on whether our understanding of nuclear structure evolution in this mass region is correct. [Copyright &y& Elsevier]

Despite a lot of experimental and theoretical progress the question of the r-process site and the origin of the heavy elements in nature remains one of the biggest open questions in nuclear astrophysics. I discuss the need for experimental nuclear data and review recent progress made at rare isotope beam facilities. In particular, I summarize some recent experiments performed at the NSCL Coupled Cyclotron Facility at MSU with beams of r-process nuclei, including the measurement of the half-life of 78Ni. [Copyright &y& Elsevier]

With new data from RXTE, Chandra, and XMM X-ray astronomy of accreting neutron stars enters a precision era. Precision nuclear physics from experiments with radioactive beams is needed to interpret the data. We review status and prospects of the nuclear physics, focusing on the nuclear reactions in X-ray bursts, in particular with heavy unstable nuclei beyond magnesium. At the NSCL Coupled Cyclotron Facility some of the major nuclear physics uncertainties are now being addressed using neutron removal reactions with radioactive beams. [Copyright &y& Elsevier]

Nuclei far from stability play an important role in our understanding of astrophysical scenarios with extreme temperature and density conditions. Among these are nova explosions, accreting neutron stars, supernovae, and the site of the r-process. I will give a brief review of the important open astrophysical questions in these scenarios and discuss the radioactive beam experiments at ISOL-type and at fragmentation-type facilities that are needed to answer them. [Copyright &y& Elsevier]

We report the first experimental constraints on spectroscopic factors and strengths of key resonances in the P 30 ( p , γ ) S 31 reaction critical for determining the production of intermediate-mass elements up to Ca in nova ejecta. The P 30 ( d , n ) S 31 reaction was studied in inverse kinematics using the GRETINA γ -ray array to measure the angle-integrated cross-sections of states above the proton threshold. In general, negative-parity states are found to be most strongly produced but the absolute values of spectroscopic factors are typically an order of magnitude lower than predicted by the shell-model calculations employing WBP Hamiltonian for the negative-parity states. The results clearly indicate the dominance of a single 3 / 2 − resonance state at 196 keV in the region of nova burning T ≈ 0.10 – 0.17 GK , well within the region of interest for nova nucleosynthesis. Hydrodynamic simulations of nova explosions have been performed to demonstrate the effect on the composition of nova ejecta. [ABSTRACT FROM AUTHOR]

Abstract: A summary of the importance of rare isotopes in the understanding of the origin of the elements and accreting neutron stars is presented. [Copyright &y& Elsevier]

The astrophysical p-process is responsible for the origin of the proton rich nuclei,which are heavier than iron. A huge network involving thousands of reaction rates is necessary to calculate the final p-abundances. But not all rates included in the network have a strong influence on the p-nuclei abundances. The p-process was investigated using a full nuclear reaction network for a type II supernova explosion when the shock front passes through the O/Ne layer. Calculations were done with a multi-layer model adopting the seed of a pre-explosion evolution of a 25 mass star. In extensive simulations we investigated the impact of single reaction rates on the final p-abundances. The results are important for the strategy of future experiments in this field. [Copyright &y& Elsevier]

The slow β -decay of the 68 Se waiting point in the astrophysical rp-process can in principle be bypassed by a sequential two proton capture. The rate of this reaction sequence depends exponentially on the 69 Br proton separation energy. We studied β -delayed proton emission of 69 Kr and extracted a proton separation energy of − 641 ( 42 ) keV . In addition, we determined a 69 Kr β -decay half-life of T 1 / 2 = 28 ( 1 ) ms and an excitation energy of 3153(55) keV of the 69 Kr isobaric analog state in 69 Br. X-ray burst model calculations show that regardless of the values of other uncertain masses in the region, the new S p ( Br 69 ) allows for a reaction flow via Se 68 ( 2 p , γ ) of at most 20%. Uncertainties are sufficiently reduced to conclude that Se 68 ( 2 p , γ ) has at best a very small effect on burst light curve and composition, and that 68 Se is a strong rp-process waiting point. Our results also exclude the possibility of a suggested longer lived, so far unobserved, 69 Br ground state. [ABSTRACT FROM AUTHOR]

Abstract: The astrophysically important states in 26Si have been studied with different reactions because of their dominant contribution to the 25Al(p,γ)26Si reaction rate at nova temperatures. We performed two different experiments to study the states of interest in 26Si, with the aim of reducing the main uncertainty in the current 25Al(p,γ)26Si rate by determining the level parameters of the dominant states more accurately. One is the p(27Si,26Si*)d experiment at NSCL, in which we measured the gamma-ray decays from the excited states in 26Si. The other one is the 25Al+p elastic scattering experiment with CRIB at RIKEN. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

The level structure of 30S was studied at the NSCL by using neutron removal reactions with a radioactive 31S beam. The γ-decay from excited states in 30S was measured in a Ge-detector array. The results discussed for this work will reduce the uncertainties in the determination of the astrophysical 29P(p,γ)30S reaction rate under rp-process conditions. [Copyright &y& Elsevier]

The light curves of type I X-ray bursts (XRBs) result from energy released from the atmosphere of a neutron star when accreted hydrogen and helium ignite and burn explosively via the rp-process. Since charged particle reaction rates are both density and very temperature dependent, a simulation model must provide accurate values of these variables to predict the reaction flow. This paper uses a self-consistent one-dimensional model calculation with a constant accretion rate of and reports on the detailed rp-process reaction flow of a given burst. [Copyright &y& Elsevier]

The 58Ni(t,3He)58Co reaction at 112 MeV/nucleon was measured to identify strength associated with Gamow-Teller transitions in the direction. The experiment is a test case for future similar studies. The main aim of such studies is to test theoretical models used to predict Gamow-Teller strength distributions that serve as input for supernovae evolution calculations. The results indicate that the (t,3He) reaction is indeed a powerful tool to perform such tests. [Copyright &y& Elsevier]

The regions around the doubly magic nuclei 100Sn and 78Ni are of great interest from a nuclear structure standpoint. These nuclei also play a key role in the astrophysical rp- and r-processes, respectively. Recently, nuclei in these regions were studied at the Coupled Cyclotron Facility at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. [Copyright &y& Elsevier]

32Mg lies within a region of deformed nuclei commonly referred to as the “island of inversion”. The β decay of 33Al and 33Mg has been studied to learn about nuclear structure near 32Mg. Decay curves and precise half-life measurements are presented for both species. Gamma-ray spectra from correlated 33Al decay events are also presented. The β-decay properties of 33Al are shown to be well-described by an sd shell model calculation, suggesting that the ground state of 33Al lies primarily outside the island of inversion. [Copyright &y& Elsevier]

Beta-decay half-lives of two nuclei close to N=Z line, 70Kr and 74Rb, have been measured at the ISOLDE mass-separator facility at CERN. Importance of these half-lives on two ingredients explaining existence and development of the Universe, the astrophysical nucleosynthesis and the Standard Model, are discussed. [Copyright &y& Elsevier]