Results 1 - 10 of 1310
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[en] A method for the determination of different ''bare'' characteristics of the one-particle motion and one-particle basis in magic nuclei is described. The method is based on separating out the mixing with phonons from the phenomenological one-particle characteristics. By means of a generalization of the procedure for localization of the mass operator, relations linking the bare and phenomenological characteristics are obtained. The radial dependence of these characteristics in finite nuclei and the influence of the quasiparticle--phonon interaction on the phenomenological characteristics are studied. Calculations are performed for the neutrons in 208Pb
[en] The reduced M2 transition probabilities 11-/21 -> 7+/21 in the odd-A isotopes 109-121Sn are found to reveal a specific behaviour. B(M2) values are calculated in the framework of the quasiparticle-phonon model. The coupling of a quasineutron with the 2+, 3- and 2- one-phonon core excitation is taken into account. Inclusion of all one-phonon 2- states up to 24 MeV in the wave functions of the excited states 11-/21 and 7+/21 reduces the theoretical B(M2) values by 3-4 times as compared to the single particle values. The specific B(M2) dependence on the mass number appears to be due to the pairing effect. (orig.)
[en] The Green's-function method has been used to obtain a general equation for the effective field in a nucleus, taking into account both 1p1h and 2p2h configurations. This equation has been used as the starting point for derivation of a previously developed microscopic model of taking 1p1h+phonon configurations into account in magic nuclei. The equation for the density matrix is analyzed in this model. It is shown that the number of quasiparticles is conserved. An equation is obtained for the effective field in the coordinate representation, which provides a formulation of the problem in the 1p1h+2p2h+continuum approximation. The equation is derived and quantitatively analyzed in the space of one-phonon states
[en] The coupling of elementary excitation modes in hot nuclei is studied. For this aim the quasiparticle-phonon nuclear model (QPM) is extended to a finite temperature by using the formalism of the thermo field dynamics. First the energies and structures of one-phonon states are calculated in the thermal random phase approximation and then the thermal QPM Hamiltonian HQPM is expressed in terms of thermal quasiparticles and thermal RPA-phonons. The equation for the energies taking into account mixing of one-and two-thermal phonon states is derived. The expression of the coupling matrix element between thermal phonons is given. 15 refs. (author)
[en] An enhanced theory, based on the Extended Boson Approximation, for the lowest-lying states in odd-mass nuclei is presented. Our approach has built on the Quasi-particle Phonon Model extending it to take into account the ground state correlations due to the action of the Pauli principle more accurately than in the conventional theory.
[en] A non-spurious quasi-particle scheme is presented, its number-projection being exactly the broken-pair model. From this property, quantities needed in the broken-pair approach are easily evaluated by making use of the extreme simplicity of the quasi-particle algebra. Applications to the Hamiltonian operator and to one-body operators are presented for seniority v=0, 1 and 2
[en] The quasiparticle-phonon model is adopted to investigate the microscopic structure of some low-lying states (known as mixed-symmetry states) recently discovered in nuclei around closed shells. The study determines quantitatively the phonon content of these states and shows that their main properties are determined by a subtle competition between particle-particle and particle-hole quadrupole interactions and by the interplay between orbital and spin-flip motion.