Contribution of excited states to stellar weak-interaction rates in odd-A nuclei

Weak-interaction rates, including beta-decay and electron capture, are studied in several odd-A nuclei in the pf-shell region at various densities and temperatures of astrophysical interest. Special attention is paid to the relative contribution to these rates of thermally populated excited states in the decaying nucleus. The nuclear structure involved in the weak processes is studied within a quasiparticle random-phase approximation with residual interactions in both particle-hole and particle-particle channels on top of a deformed Skyrme Hartree-Fock mean field with pairing correlations. In the range of densities and temperatures considered, it is found that the total rates do not differ much from the rates of the ground state fully populated. In any case, the changes are not larger than the uncertainties due to the nuclear model dependence of the rates.Comment: 13 pages, 20 figures. arXiv admin note: substantial text overlap with arXiv:1304.215

Self-consistent calculations of electron-capture decays in Z=118, 119, and 120 superheavy isotopes

Weak decays in superheavy nuclei with proton numbers Z = 118 - 120 and neutron numbers N = 175 - 184 are studied within a microscopic formalism based on deformed self-consistent Skyrme Hartree-Fock mean-field calculations with pairing correlations. The half-lives of beta+ decay and electron capture are compared with alpha-decay half-lives obtained from phenomenological formulas. The sensitivity of the half-lives to the unknown Q-energies is studied by comparing the results obtained from different approaches for the masses. It is shown that alpha-decay is always dominant in this mass region. The competition between alpha and beta+/EC decay modes is studied in seven alpha-decay chains starting at different isotopes of Z=118, 119, and 120.Comment: 8 pages, 5 figures. arXiv admin note: text overlap with arXiv:2009.0210

Beta-decay properties of neutron-rich medium-mass nuclei

Invited paper; Varna, Bulgaria, 7-11 September 2015; http://www.inrne.bas.bg/international-school-varna/Peer Reviewe

Electron-capture decay in isotopic transfermium chains from self-consistent calculations

Weak decays in heavy nuclei with charge numbers Z=101-109 are studied within a microscopic formalism based on deformed self-consistent Skyrme Hartree-Fock mean-field calculations with pairing correlations. The half-lives of beta+ decay and electron capture are compared with alpha-decay half-lives obtained from phenomenological formulas. Transfermium isotopes of Md, No, Lr, Rf, Db, Sg, Bh, Hs, and Mt that can be produced in the frontier of cold and hot fusion-evaporation channels are considered. Several isotopes are identified whose beta+/EC- and alpha-decay half-lives are comparable. The competition between these decay modes opens the possibility of new pathways towards the islands of stability.Comment: 14 pages, 10 figures, accepted for publication in Journal of Physics

Effects of deformation on the β -decay patterns of light even-even and odd-mass Hg and Pt isotopes

14 pags.; 16 figs.; 2 tabs.; PACS number(s): 21.60.Jz, 23.40.−s, 27.70.+q, 27.80.+w© 2015 American Physical Society. Bulk and decay properties, including deformation energy curves, charge mean square radii, Gamow-Teller (GT) strength distributions and β-decay half-lives are studied in neutron-deficient even-even and odd-A Hg and Pt isotopes. The nuclear structure is described microscopically from deformed quasiparticle random-phase approximation calculations with residual interactions in both particle-hole and particle-particle channels, performed on top of a self-consistent deformed quasiparticle Skyrme Hartree-Fock basis. The observed sensitivity of the not-yet-measured GT strength distributions to deformation is proposed as an additional complementary signature of the nuclear shape. The β-decay half-lives resulting from these distributions are compared to experiment to demonstrate the ability of the method.This work was supported by Ministerio de Economíıa y Competitividad (Spain) under Contract No. FIS2011–23565 and the Consolider–Ingenio 2010 Programs CPAN CSD2007-00042.Peer Reviewe

Gamow-Teller response in deformed even and odd neutron-rich Zr and Mo isotopes

beta-decay properties of neutron-rich Zr and Mo isotopes are investigated within a microscopic theoretical approach based on the proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme Hartree-Fock calculations with pairing correlations. Residual separable particle-hole and particle-particle forces are also included in the formalism. The structural evolution in these isotopic chains including both even and odd isotopes is analyzed in terms of the equilibrium deformed shapes. Gamow-Teller strength distributions, beta-decay half-lives, and beta-delayed neutron-emission probabilities are studied, stressing their relevance to describe the path of the nucleosynthesis rapid neutron capture process

Evolution of nuclear shapes in medium mass isotopes from a microscopic perspective

13 pages, 12 figures.-- PACS nrs.: 21.60.Jz; 21.60.Fw; 27.60.+j; 27.70.+q.The self-consistent Hartree-Fock-Bogoliubov approximation based on the finite-range and density-dependent Gogny interaction (parametrization D1S) has been used to generate potential energy curves in various chains of Pd, Xe, Ba, Nd, Sm, Gd, and Dy isotopes. The evolution of shapes with the number of nucleons is studied and a search for signatures of E(5) and X(5) critical point symmetries is also conducted. The results are compared with those obtained in the framework of other mean-field approximations to the nuclear many-body problem. The role of triaxiality in nuclei where this degree of freedom could be relevant is considered and discussed.This work was partly supported by Ministerio de Educación y Ciencia (Spain) under Contract Nos. FIS2005-00640 and FPA2007-66069.Peer reviewe

Deformed quasiparticle random phase approximation formalism for single- and two-neutrino double β decay

13 pages, 4 tables, 18 figures.-- PACS nrs.: 21.60.Jz; 23.40.Hc; 23.40.Bw.We use a deformed quasiparticle random phase approximation formalism to describe simultaneously the energy distributions of the single β Gamow-Teller strength and the two-neutrino double β decay matrix elements. Calculations are performed in a series of double β decay partners with A=48 , 76, 82, 96, 100, 116, 128, 130, 136, and 150, using deformed Woods-Saxon potentials and deformed Skyrme Hartree-Fock mean fields. The formalism includes a quasiparticle deformed basis and residual spin-isospin forces in the particle-hole and particle-particle channels. We discuss the sensitivity of the parent and daughter Gamow-Teller strength distributions in single β decay, as well as the sensitivity of the double β decay matrix elements to the deformed mean field and to the residual interactions. Nuclear deformation is found to be a mechanism of suppression of the two-neutrino double β decay. The double β decay matrix elements are found to have maximum values for about equal deformations of parent and daughter nuclei. They decrease rapidly when differences in deformations increase. We remark on the importance of a proper simultaneous description of both double β decay and single Gamow-Teller strength distributions. Finally, we conclude that for further progress in the field, it would be useful to improve and complete the experimental information on the studied Gamow-Teller strengths and nuclear deformations.We would like to thank A. A. Raduta for useful discussions. This work was supported by Ministerio de Educación y Ciencia (Spain) under Contract No. BFM2002-03562 and by International Graduiertenkolleg GRK683, by the “Land Baden-Wuerttemberg” within the “Landesforschungsschwerpunkt: Low Energy Neutrinos,” by the DFG under 418SPA112/8/03, the VEGA Grant agency of the Slovac Republic under Contract No. 1/0249/03, and by the EU ILIAS project under Contract No. RII3-CT-2004-506222. One of us (R.A.R.) thanks Ministerio de Educación y Ciencia (Spain) for financial support.Peer reviewe

Effective density-dependent pairing forces in the T=1 and T=0 channels

Effective density-dependent pairing forces of zero range are adjusted on gap values in T = 0,1 channels calculated with the Paris force in symmetric nuclear matter. General discussions on the pairing force are presented. In conjunction with the effective k mass the nuclear pairing force seems to need very little renormalization in the T = 1 channel. The situation in the T = 0 channel is also discussed.This work was supported by DGICYT-IN2P3 agreement and by DGICYT (Spain) under Contract No. PB95/0123.Peer reviewe

Question of low-lying intruder states in Be-8 and neighboring nuclei

The presence of not yet detected intruder states in Be-8, e.g., a J = 2(+) intruder at 9 MeV excitation would affect the shape of the beta(-/+)-delayed alpha spectra of Li-8 and B-8. In order to test the plausibility of this assumption, shell-model calculations with up to 4 (h) over bar omega excitations in Be-8 (and up to 2 (h) over bar omega excitations in Be-10) were performed. With the above restrictions on the model spaces, the calculations did not yield any low-lying intruder state in Be-8. Another approach-the simple deformed oscillator model with self-consistent frequencies and volume conservation-gives an intruder state in 8Be which is lower in energy than the above shell-model results, but its energy is still considerably higher than 9 MeV.This work was supported by Department of Energy Grant No. DE-FG02-95ER40940, by DGICYT -Spain grants under Contracts No. PB95/0123 and SA95-0371.Peer reviewe