Search results for "r-process"
showing 10 items of 74 documents
Dependence of direct neutron capture on nuclear-structure models
1998
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…
Coulomb breakup of psd-shell neutron-rich nuclei
2005
Inelastic scattering of loosely bound nuclei by Coulomb interaction at intermediate energies (400?600 MeV/nucleon) has been utilized as a spectroscopic tool for exotic nuclei. The observed electromagnetic dipole (E1) strength above the one neutron threshold of neutron-rich C, Be, B and O isotopes can be explained by a non-resonant transition of a neutron into the continuum. The shape of these strength distributions reflects properties of the wavefunction of the released neutron in the nucleus and hence ground-state properties of these isotopes. Neutron capture cross-sections such as for the 14C(n,?) 15C reaction which are of astrophysical relevance can be deduced indirectly.
Origin of the odd-even staggering in theA?80 solarR-abundance peak
1990
In contrast to the conventional picture, the r-process yields in the A≃80 abundance peak exhibit a pronounced odd-even staggering. It is proposed that this behaviour may be due to strong β-delayed neutron branching from a few odd-mass isotopes located in or close to the r-process path.
The r-process in the high entropy bubble
1997
We examined the r-process in the high entropy bubble within a detailed parameter study. Previous investigations ([1,2]) based on realistic supernovae models showed already that this model yields a very good fit to the solar system r-process abundance curve for masses above A = 120. For A < 120 their fit was relatively poor. We are concerned mainly with the question whether it is possible to obtain a good fit in the range below A = 120. Within a simple approach of an adiabatically expanding sphere we analyzed a broad parameter range, independent of specific explosion simulations. We varyied the electron abundance Ye and the entropy S and studied the resulting contributions as a function of t…
Nuclear Level Density and the Determination of Thermonuclear Rates for Astrophysics
1997
The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. We discuss the model mostly employed for such calculations: the statistical model (Hauser-Feshbach). Special emphasis is put on the uncertainties arising from nuclear level density descriptions and an improved global description is presented. Furthermore, criteria for the applicability of the statistical model are investigated and a "map" for the applicability of the model to reactions of stable and unstable nuclei with neutral and charged particles is given.
Ion implant-β-decay correlation half-lives in a pulsed beam for isotopes beyond N=126
2018
Half-lives and β-delayed neutron emission probabilities of several isotopes of Au, Hg, Tl, Pb and Bi, in the neutron-rich region around and beyond N=126, were determined in an experiment performed at the RIB facility of GSI [1]. These are decay properties that are directly related to the final abundance distribution of the elements due to their contribution during the freeze-out of the r-process nucleosynthesis. This contribution summarizes the main aspects of the analysis methodology followed for the determination of β-decay half-lives. The main particularities of the present analysis concern the characterization of the β-background, as well as the effect of the pulsed-beam in the ion-β ti…
Nuclear Structure Properties of Neutron Rich Ge-Br Isotopes in the Astrophysical r-Process
2006
The astrophysical r-process is responsible for synthesis of roughly half of the elements heavier than iron. In spite of this significance, there are many uncertainties regarding the site of the r-process and the neutron-rich nuclei involved. Studying these nuclei presents a challenge, as they lie far from the valley of stability. Nuclear properties such as β decay half-lives and βdelayed neutron emission probabilities are critical inputs for r-process models. The neutron rich Ge-Br isotopes are in the region just after the N=50 bottle neck in the “classical” r-process, or may serve as seed material for the high entropy neutrino-wind r-process. Neutron rich nuclei play an important role in b…
Constraints on r-process conditions from beta-decay properties far off stability and r-abundances.
1988
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.
β decay of67Co
1999
The \ensuremath{\beta}-decay properties of ${}^{67}\mathrm{Co}$ produced in proton-induced fission of ${}^{238}\mathrm{U}$ were measured by the detection of \ensuremath{\beta}-delayed \ensuremath{\gamma} rays emitted from an isotopically pure mass-separated source obtained by laser ionization. The measured half-life of 0.425(20) s is more accurate than previous values. New \ensuremath{\gamma} transitions were observed, and corresponding branching ratios and $\mathrm{log}\mathrm{ft}$ values were deduced. The ${}^{67}\mathrm{Co}$ decay scheme is discussed in terms of the single-particle shell model.
Application of the relativistic mean-field mass model to ther-process and the influence of mass uncertainties
2008
A new mass table calculated by the relativistic mean-field approach with the state-dependent BCS method for the pairing correlation is applied for the first time to study r-process nucleosynthesis. The solar r-process abundance is well reproduced within a waiting-point approximation approach. Using an exponential fitting procedure to find the required astrophysical conditions, the influence of mass uncertainty is investigated. The r-process calculations using the FRDM, ETFSI-Q, and HFB-13 mass tables have been used for that purpose. It is found that the nuclear physical uncertainty can significantly influence the deduced astrophysical conditions for the r-process site. In addition, the infl…