L. Pacearescu

Publications (12)2.11 Total impact

• Source

  Available from: Friedrich -K. Thielemann

  Article: Large-scale prediction of the parity distribution in the nuclear level density and application to astrophysical reaction rates

  D. Mocelj, T. Rauscher, G. Martinez-Pinedo, K. Langanke, L. Pacearescu, A. Faessler, F. -K. Thielemann, Y. Alhassid
  [show abstract] [hide abstract]
  ABSTRACT: A generalized method to calculate the excitation-energy dependent parity ratio in the nuclear level density is presented, using the assumption of Poisson distributed independent quasi particles combined with BCS occupation numbers. It is found that it is crucial to employ a sufficiently large model space to allow excitations both from low-lying shells and to higher shells beyond a single major shell. Parity ratios are only found to equilibrate above at least 5-10 MeV of excitation energy. Furthermore, an overshooting effect close to major shells is found where the parity opposite to the ground state parity may dominate across a range of several MeV before the parity ratio finally equilibrates. The method is suited for large-scale calculations as needed, for example, in astrophysical applications. Parity distributions were computed for all nuclei from the proton dripline to the neutron dripline and from Ne up to Bi. These results were then used to recalculate astrophysical reaction rates in a Hauser-Feshbach statistical model. Although certain transitions can be considerably enhanced or suppressed, the impact on astrophysically relevant reactions remains limited, mainly due to the thermal population of target states in stellar reaction rates.
  04/2007;
• Source

  Available from: arxiv.org

  Article: Effect of deformation on two-neutrino double beta decay matrix elements

  R. Alvarez-Rodriguez, P. Sarriguren, E. Moya de Guerra, L. Pacearescu, A. Faessler, F. Simkovic
  [show abstract] [hide abstract]
  ABSTRACT: We study the effect of deformation on the two-neutrino double beta decay for ground state to ground state transitions in all the nuclei whose half-lives have been measured. Our theoretical framework is a deformed QRPA based in Woods-Saxon or Hartree-Fock mean fields. We are able to reproduce at the same time the main characteristics of the two single beta branches, as well as the double beta matrix elements. We find a suppression of the double beta matrix element with respect to the spherical case when the parent and daughter nuclei have different deformations.
  04/2006;
• Source

  Available from: arxiv.org

  Article: A deformed QRPA formalism for single and two-neutrino double beta decay

  R. Alvarez-Rodriguez, P. Sarriguren, E. Moya de Guerra, L. Pacearescu, A. Faessler, F. Simkovic
  [show abstract] [hide abstract]
  ABSTRACT: We use a deformed QRPA formalism to describe simultaneously the energy distributions of the single beta Gamow-Teller strength and the two-neutrino double beta decay matrix elements. Calculations are performed in a series of double beta 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 beta decay, as well as the sensitivity of the double beta 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 beta decay. The double beta 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 the importance of a proper simultaneous description of both double beta 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. Comment: 33 pages, 19 figures. To be published in Phys. Rev. C
  11/2004;
• Source

  Available from: Friedrich -K. Thielemann

  Article: Parity-Dependence in the Nuclear Level Density

  D. Mocelj, T. Rauscher, G. Martinez-Pinedo, K. Langanke, L. Pacearescu, A. Faessler, F. -K. Thielemann
  [show abstract] [hide abstract]
  ABSTRACT: Astrophysical reaction rates are sensitive to the parity distribution at low excitation energies. We combine a formula for the energy-dependent parity distribution with a microscopic-macroscopic nuclear level density. This approach describes well the transition from low excitation energies, where a single parity dominates, to high excitations where the two densities are equal.
  08/2004;
• Article: Nuclear deformation and the double-beta decay

  L. Pacearescu, A. Faessler, F. Šimkovic
  [show abstract] [hide abstract]
  ABSTRACT: The effect of deformation on the two-neutrino double-beta decay (2νββ decay) for ground-state transition 76Ge → 76Se is studied in the framework of the deformed QRPA with separable Gamow-Teller residual interaction. A new suppression mechanism of the 2νββ-decay matrix element based on the difference in deformations of the initial and final nuclei is reported. An advantage of this suppression mechanism in comparison with that associated with ground-state correlations is that it allows a simultaneous description of the single-β and the 2νββ decay.
  Physics of Atomic Nuclei 05/2004; 67(6):1210-1215. · 0.57 Impact Factor
• Article: Two-neutrino double β decay within fully renormalized quasiparticle random-phase approximation: Effect of the restoration of the Ikeda sum rule

  L. Pacearescu, V. Rodin, F. Šimkovic, Amand Faessler
  [show abstract] [hide abstract]
  ABSTRACT: The recently proposed fully renormalized quasiparticle random-phase approximation (QRPA), which fulfills the Ikeda sum rule exactly, is applied to the two-neutrino double β decay of 76Ge, 82Se, 100Mo, 116Cd, 128Te, and 130Xe. The results obtained are compared with those of other approaches, standard QRPA and self-consistent QRPA. The similarities and the differences among the methods are discussed. The influence of the restoration of the Ikeda sum rule on the 2νββ-decay amplitude is analyzed.
  Phys. Rev. C. 12/2003; 68(6).
• Source

  Available from: arxiv.org

  Article: Two-neutrino double beta decay within Fully-Renormalized QRPA: Effect of the restoration of the Ikeda sum rule

  L. Pacearescu, V. Rodin, F. Simkovic, Amand Faessler
  [show abstract] [hide abstract]
  ABSTRACT: The recently proposed Fully-Renormalized QRPA (FR-QRPA), which fullfils the Ikeda sum rule (ISR) exactly, is applied to the two-neutrino double beta decay of $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{116}$Cd, $^{128}$Te and $^{130}$Xe. The results obtained are compared with those of other approaches, standard QRPA and self-consistent QRPA (SCQRPA). The similarities and the differences among the methods are discussed. The influence of the restoration of the Ikeda sum rule on the $2\nu\beta\beta$-decay amplitude is analyzed. Comment: 20 pages, 8 figures
  08/2003;
• Source

  Available from: Apolodor Raduta

  Article: Gamow-Teller strength distributions in 76Ge and 76Se from deformed QRPA

  P. Sarriguren, E. Moya de Guerra, L. Pacearescu, Amand Faessler, F. Simkovic, A. A. Raduta
  [show abstract] [hide abstract]
  ABSTRACT: We study Gamow-Teller strength distributions of 76Ge and 76Se within a deformed QRPA formalism, which includes residual spin-isospin forces in the particle-hole and particle-particle channels. We consider two different methods to construct the quasiparticle basis, a selfconsistent approach based on a deformed Hartree-Fock calculation with density-dependent Skyrme forces and a more phenomenological approach based on a deformed Woods-Saxon potential. Both methods contain pairing correlations in the BCS approach. We discuss the sensitivity of Gamow-Teller strength distributions to the deformed mean field and residual interactions.
  04/2003;
• Article: Semi-classical treatment of the proton-neutron two body interaction

  A. A. Raduta, L. Pacearescu, V. Baran, P. Sarriguren, E. Moya de Guerra
  Nuclear Physics A 01/2000; 675:503. · 1.54 Impact Factor
• Source

  Available from: Friedrich -K. Thielemann

  Article: Towards a parity-dependent level density for astrophysics

  D Mocelj, T Rauscher, F-K Thielemann, G Martínez Pinedo, K Langanke, L Pacearescu, A Fäßler
  [show abstract] [hide abstract]
  ABSTRACT: Astrophysical reaction rates are sensitive to the parity distribution at low excitation energies. We combine a formula for the energy-dependent parity distribution with a microscopic-macroscopic nuclear level density. This approach describes well the transition from low excitation energies where a single parity dominates to high excitations where the two densities are equal.
• Article: Gamow-Teller strength distributions in^{76} Ge and^{76} Se from deformed quasiparticle random-phase approximation

  P. Sarriguren, E. Moya de Guerra, L. Pacearescu, Amand Faessler, F. Šimkovic, A. A. Raduta
  [show abstract] [hide abstract]
  ABSTRACT: We study Gamow-Teller strength distributions of 76Ge and 76Se within a deformed quasiparticle random-phase approximation formalism, which includes residual spin-isospin forces in the particle-hole and particle-particle channels. We consider two different methods to construct the quasiparticle basis, a self-consistent approach based on a deformed Hartree-Fock calculation with density-dependent Skyrme forces and a more phenomenological approach based on a deformed Woods-Saxon potential. Both methods contain pairing correlations in the BCS approach. We discuss the sensitivity of Gamow-Teller strength distributions to the deformed mean field and residual interactions.
  Phys. Rev. C. 67(4).
• Article: Deformed quasiparticle random phase approximation formalism for single-and two-neutrino double β decay

  R. Álvarez-Rodríguez, P. Sarriguren, E. Moya de Guerra, L. Pacearescu, Amand Faessler, F. Šimkovic
  [show abstract] [hide abstract]
  ABSTRACT: 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.
  Phys. Rev. C. 70(6).