arXiv subjects

A. A. Raduta

Publications and source records attributed to A. A. Raduta.

63 records · Page 4Linked to original sources

arXiv2003

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

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.

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arXiv2002

New features of collective motion of intrinsic degrees of freedom. Toward a possible way to classify the intrinsic states

Three exactly solvable Hamiltonians of complex structure are studied in the framework of a semi-classical approach. The quantized trajectories for intrinsic coordinates correspond to energies which may be classified in collective bands. For two of the chosen Hamiltonians the symmetry SU2xSU2 is the appropriate one to classify the eigenvalues in the laboratory frame. Connections of results presented here with the molecular spectrum and Moszkowski model are pointed out. The present approach suggests that the intrinsic states, which in standard formalisms are heading rotational bands, are forming themselves "rotational" bands, the rotations being performed in a fictious boson space.

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arXiv2001

Unified description of three positive and three negative parity interacting bands

The coherent state model (CSM) is extended so that three negative parity bands are treated on equal footing with three positive parity bands. The six rotational bands are generated by projecting out angular momenta and parities from three intrisic orthogonal states which exhibit both quadrupole and octupole deformations. The projected states are, by construction, mutually orthogonal. In the space of projected states, a sub-space of a quadrupole and octupole multi-boson states, an effective quadrupole and octupole boson Hamiltonian is solved. The eigenstates of the model Hamiltonian are linked by multipole transition operators for which lowest order boson expressions are considered. The calculations involve 6 structure coefficients and two deformation parameters. All of them are fixed by a least square fit of the known experimental energies. Applications are made to Gd158, Yb172, Ra218, Ra226, Th232, U238, Pu238. Very good agreement is obtained for both excitation energies and transition probabilities. New signatures for octupole deformation, manifested in excited bands, are pointed out.

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arXiv2001

Neutrinoless Double Beta Decay of Ge76, Se82, Mo100 and Xe136 to excited 0^+ states

The neutrinoless double beta decay transition to the first excited 0^+ collective final state is examined for A=76, 82, 100 and 136 nuclei by assuming light and heavy Majorana neutrino exchange mechanisms as well as the trilinear R-parity violating contributions. Realistic calculations of nuclear matrix elements have been performed within the renormalized quasiparticle random phase approximation. Transitions to the first excited two-quadrupole phonon 0^+ state are described within a boson expansion formalism and alternatively by using the operator recoupling method. We present the sensitivity parameters to different lepton number violating signals, which can be used in planning the neutrinoless double beta decay experiments. The half-life of neutrinoless double beta decay to the first excited state 0^+_1 is by a factor of 10 to 100 larger than that of the transition to the ground state.

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arXiv2001

Description of collective magnetic states within a spherical single particle basis

A many body Hamiltonian comprising pairing, quadrupole-quadrupole and spin-spin interaction is treated within a projected spherical basis with the aim of describing the detailed structure of the magnetic states of orbital and spin-flip nature in $^{144, 148-154}$Sm. The mean field for the single particle motion takes care of the volume conservation of a phenomenological core which results in having a complex dependence on deformation for single particle energies. Several experimental features like the total orbital and total spin strengths, the shape of the orbital strength distribution, the hump structure of the spin strength distribution, the quadratic dependence of the orbital strength on nuclear deformation, the saturation effect of the orbital strength with respect to the Casten's factor P are very well described within a quasiparticle random phase approximation formalism. Comparison of present results with those obtained in some previous treatments are also given.

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arXiv2001

Ground state particle-particle correlations and double beta decay

A self-consistent formalism for the double beta decay of Fermi type is provided. The particle-particle channel of the two-body interaction is considered first in the mean field equations and then in the QRPA. The resulting approach is called the QRPA with a self-consistent mean field (QRPASMF). The mode provided by QRPASMF, does not collapse for any strength of the particle-particle interaction. The transition amplitude for double beta decay is almost insensitive to the variation of the particle-particle interaction. Comparing it with the result of the standard pnQRPA, it is smaller by a factor 6. The prediction for transition amplitude agrees quite well with the exact result. The present approach is the only one which produces a strong decrease of the amplitude and at the same time does not alter the stability of the ground state.

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arXiv2001

New results for two-neutrino double beta decay with large particle-particle two body proton-neutron interaction

A model many-body Hamiltonian describing an heterogenous system of paired protons and paired neutrons and interacting among themselves through monopole particle-hole and monopole particle-particle interactions is used to study the double beta decay of Fermi type. The states are described by time dependent approaches choosing as trial functions coherent states of the symmetry groups underlying the model Hamiltonian. One formalism, VP1, is fully equivalent with the standard pnQRPA and therefore fails at a critical value of the particle-particle interaction strength while another one, VP2, corresponds to a two step BCS treatment, i.e. the proton quasiparticles are paired with the neutron quasiparticles. In this way a harmonic description for the double beta transition amplitude is provided for any strength of the particle-particle interaction. The approximation quality is judged by comparing the actual results with the exact result as well as with those corresponding to various truncations of the boson expanded Hamiltonian and transition operator. Finally it is shown that the dynamic ground states provided by VP1 and VP2 are reasonable well approximated by solutions of a variational principle. This remark constitutes a step forward finding an approach where the RPA ground state is a solution of a variational principle equation.

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arXiv2001

Quasiparticle Random Phase Approximation with an optimal Ground State

A new Quasiparticle Random Phase Approximation approach is presented. The corresponding ground state is variationally determined and exhibits a minimum energy. New solutions for the ground state, some with spontaneously broken symmetry, of a solvable Hamiltonian are found. A non-iterative procedure to solve the non-linear QRPA equations is used and thus all possible solutions are found. These are compared with the exact results as well as with the solutions provided by other approaches.

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arXiv1998

Description of even-even triaxial Nuclei within the Coherent State and the Triaxial Rotation-Vibration Models

The coherent state model (CSM) and the triaxial rotation-vibration model (TRVM) are alternatively used to describe the ground, gamma and beta bands of 228Th. CSM is also applied to the nuclei 126Xe and 130Ba, which were recently considered in TRVM. The two models are compared with respect to both their underlying assumptions and to their predicted results for energy levels and E2 branching ratios. Both models describe energies and quadrupole transitions of 228Th equally well and in good agreement with experiment, if the 0$_3^+$ level at 1120 keV is interpreted as the head of the beta band. The other two 0$^+$ levels at 832 and 939 keV are most likely not of a pure quadrupole vibration nature as has already been pointed out in the literature.

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