0000000000200921
AUTHOR
P. Möller
rp-process nucleosynthesis at extreme temperature and density conditions
We present nuclear reaction network calculations to investigate the influence of nuclear structure on the rp-process between Ge and Sn in various scenarios. Due to the lack of experimental data for neutron-deficient nuclei in this region, we discuss currently available model predictions for nuclear masses and deformations as well as methods of calculating reaction rates (Hauser-Feshbach) and beta-decay rates (QRPA and shell model). In addition, we apply a valence nucleon (NpNn) correlation scheme for the prediction of masses and deformations. We also describe the calculations of 2p-capture reactions, which had not been considered before in this mass region. We find that in X-ray bursts 2p-c…
Constraints on r-process conditions from beta-decay properties far off stability and r-abundances.
The measured beta -decay properties of the 'waiting-point' nuclei 130Cd and 80Zn, together with improved shell model predictions of T1/2 and Pn-values for their experimentally unknown N approximately=82 and 50 neighbours, can be directly related to the observed r-abundances in the A approximately=130 and 80 abundance peaks. Based on this result, new constraints are given on the stellar conditions under which the r-process has operated.
Neutron-rich isotopesTi54−57
The neutron-rich isotopes $^{54\mathrm{\ensuremath{-}}57}\mathrm{Ti}$ and $^{58\mathrm{\ensuremath{-}}60}\mathrm{Cr}$ are produced by fragmentation of a 64.5 MeV/nucleon $^{65}\mathrm{Cu}^{26+}$ beam in a 90 mg/${\mathrm{cm}}^{2}$ $^{9}\mathrm{Be}$ target. Following particle identification by energy loss and time of flight, the radioactive decay was observed by \ensuremath{\beta} singles and \ensuremath{\beta}\ensuremath{\gamma}-coincidence measurements. The results obtained for $^{58\mathrm{\ensuremath{-}}60}\mathrm{Cr}$ are compared to previous results, whereas the decay of the $^{54\mathrm{\ensuremath{-}}57}\mathrm{Ti}$ isotopes is studied here. \ensuremath{\gamma}-ray intensities and en…
Rotational bands in99Sr
The β-decay of 59 ms99Rb has been studied at OSTIS. As is confirmed by RPA calculations with Nilsson model wave functions, the lowest energy levels in99Sr are consistent with rotational bands built on the [411 3/2], [413 5/2] and [422 3/2] Nilsson neutron configurations at 0, 423 and 1071 keV, respectively. All three bands have similar values of the inertial parameter ħ2/2θ indicating a nearly rigid rotor.
Nuclei Far from Stability and the R-Process Waiting-Point Concept
The nucleosynthesis process by rapid neutron captures (the r-process) is responsible for the formation of about half of the nuclear species in nature beyond Fe. While the astrophysical site for the r-process is not yet unambiguously identified, its association with the cores of low-mass stars undergoing type II supernova (SN) events is strongly suggested (see, e.g., Refs.1,2).
Stability and decay of nuclei at the end of the periodic system
Abstract Recent studies of nuclear mass models show that it is essential to account for the Coulomb redistribution energy when calculating the nuclear potential energy in the heavy-element region. Results obtained by use of a mass model that includes Coulomb redistribution effects are analyzed. Q -values for α- and β-decay are calculated. Half-lives for α-decay are estimated by use of the Viola-Seaborg systematics. For EC, β + decay and β − decay, half-lives are calculated in a microsciopic QRPA model. Calculated single-particle level structures in the heavy-element region are presented. These indicate possible regions of isomers that would be unusually stable with respect to spontaneous fi…
First beta-decay studies of the neutron-rich isotopes 53-55Sc and 56-59V
The neutron-rich isotopes Sc53-55 and V56-59 have been produced at GANIL in interactions of a 64.5 MeV/u Cu-65 beam with a Be-9 target. They were separated by the doubly achromatic spectrometer LISE3. Beta-decay half-lives and subsequent low-energy gamma-rays were observed for the first time. The present results are compared to QRPA model predictions. The quick drop of the half-life observed at N = 33 for Ca-53(20)33 is water V-56(23)33 and absent for Sc-54(21)33, indicating a vanishing of the N = 32 subshell north to Ca-52(32). In an astrophysical context, these neutron-rich isotopes represent r-process progenitors which, after beta-decay, would produce the correlated isotopic over-abundan…
Interpretation of the SolarCa48/Ca46Abundance Ratio and the Correlated Ca-Ti Isotopic Anomalies in the EK-1-4-1 Inclusion of the Allende Meteorite
$\ensuremath{\beta}$-delayed neutron-emission probabilities of neutron-rich S to K isotopes are calculated with nuclear-structure effects taken into account. These results strongly affect predictions made in high-neutron-density astrophysical scenarios for isotopic abundances of several elements. In particular, it is demonstrated that the solar abundance ratio $^{48}\mathrm{Ca}$/$^{46}\mathrm{Ca}$ as well as the correlated Ca and Ti isotopic anomalies can be explained by the same nucleosynthesis process.
New states in heavy Cd isotopes and evidence for weakening of the N = 82 shell structure
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 endpoint of the rp-process
Abstract The endpoint of rp-process nucleosynthesis in X-ray bursts determines the fuel consumption, the energy generation, and the abundance pattern of the produced nuclei. To investigate the time structure of rp-process nucleosynthesis, we used a nuclear reaction network including nuclei from H to Sn. We found that if 2p-capture reactions are included, the synthesis of nuclei heavier than Kr proceeds faster than previously thought. Therefore, in most X-ray bursts large amounts of nuclei in the A=80–100 region are expected to be produced. With an escape factor of about 1%, X-ray bursts could account for the large observed solar system abundances of the light p-nuclei like 92 Mo and 96 Ru t…
R-Process Abundances and Nuclear Properties Far from Stability
Recent measurements of β-decay properties of the ‘waiting-point’ nuclei 79Cu, 80Zn and 130Cd, together with new QRPA shell-model predictions of so far unknown N ≃ 50 and N ≃ 82 isotopes in the r-process path, have allowed to explain the detailed isotopic composition in the A ≃ 80 and A ≃ 130 r-abundance peaks. The correlation between nuclear data far from stability and r-abundances suggests that the r-process involves a high-neutron-density β-flow equilibrium environment. Based on these results, the r-process components of nuclei in the 90 ≤ A ≤ 100 mass range were predicted for freeze-out conditions (nn ≃ 1020, T9 ≃ 1) and compared to the solar-system r-process abundances.
Operation of the r-process and cosmochronology
Abstract The rapid neutron capture process produced about half of the heavy elements in nature beyond the Fe-peak. In the past quite a number of astrophysical sites have been suggested, but none of them has yet been uniquely identified. Without assuming a particular site or model, we deduce the conditions responsible for the production of r-process nuclei by making use of the following information: (1) the solar r-process abundances and (2) nuclear masses and beta decay half lives for nuclei far from stability - in particular experimental information near magic neutron numbers, which determines the shape of the r-process peaks. In addition, we review briefly galactic age determinations base…
Dependence of direct neutron capture on nuclear-structure models
The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. We calculate direct neutron capture on the even-even isotopes $^{124-145}$Sn and $^{208-238}$Pb with energy levels, masses, and nuclear density distributions taken from different nuclear-structure models. The utilized structure models are a Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a macroscopic-microscopic model based on the finite-range droplet model and a folded-Yukawa single-particle potential. Due to the differences in the resulting neutron separation and level energies, the investigated models yield capture cross sections sometimes differing by orde…