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P. P. Raychev

Publications and source records attributed to P. P. Raychev.

27 records · Page 2Linked to original sources
arXiv2001

Unified description of magic numbers of metal clusters in terms of the 3-dimensional q-deformed harmonic oscillator

Magic numbers predicted by a 3-dimensional q-deformed harmonic oscillator with Uq(3)>SOq(3) symmetry are compared to experimental data for atomic clusters of alkali metals (Li, Na, K, Rb, Cs), noble metals (Cu, Ag, Au), divalent metals (Zn, Cd), and trivalent metals (Al, In), as well as to theoretical predictions of jellium models, Woods-Saxon and wine bottle potentials, and to the classification scheme using the 3n+l pseudo quantum number. In alkali metal clusters and noble metal clusters the 3-dimensional q-deformed harmonic oscillator correctly predicts all experimentally observed magic numbers up to 1500 (which is the expected limit of validity for theories based on the filling of electronic shells), while in addition it gives satisfactory results for the magic numbers of clusters of divalent metals and trivalent metals, thus indicating that Uq(3), which is a nonlinear extension of the U(3) symmetry of the spherical (3-dimensional isotropic) harmonic oscillator, is a good candidate for being the symmetry of systems of several metal clusters. The Taylor expansions of angular momentum dependent potentials approximately producing the same spectrum as the 3-dimensional q-deformed harmonic oscillator are found to be similar to the Taylor expansions of the symmetrized Woods-Saxon and wine-bottle symmetrized Woods-Saxon potentials, which are known to provide successful fits of the Ekardt potentials.

physics.atm-clus↗
arXiv2000

Ground-gamma band mixing and odd-even staggering in heavy deformed nuclei

It is proposed that the odd-even staggering (OES) in the $γ$- bands of heavy deformed nuclei can be reasonably characterized by a discrete approximation of the fourth derivative of the odd-even energy difference as a function of angular momentum $L$. This quantity exhibits a well developed staggering pattern (zigzagging behavior with alternating signs) in rare earth nuclei and actinides with long $γ$- bands ($L\geq 10$). It is shown that the OES can be interpreted reasonably as the result of the interaction of the $γ$ band with the ground band in the framework of a Vector Boson Model with SU(3) dynamical symmetry. The model energy expression reproduces successfully the staggering pattern in all considered nuclei up to $L=12-13$. The general behavior of the OES effect in rotational regions is studied in terms of the ground--$γ$ band-mixing interaction, showing that strong OES effect occurs in regions with strong ground--$γ$ band-mixing interaction. The approach used allows a detailed comparison of the OES in $γ$ bands with the other kinds of staggering effects in nuclei and diatomic molecules.

nucl-th↗
arXiv2000

Ground-$γ$ band coupling in heavy deformed nuclei and SU(3) contraction limit

We derive analytic expressions for the energies and $B(E2)$-transition probabilities in the states of the ground and $γ$ bands of heavy deformed nuclei within a collective Vector-Boson Model with SU(3) dynamical symmetry. On this basis we examine the analytic behavior of the SU(3) energy splitting and the B(E2) interband transition ratios in the SU(3) contraction limits of the model. The theoretical analyses outline physically reasonable ways in which the ground-$γ$ band coupling vanishes. The experimental data on the lowest collective states of even-even rare earth nuclei and actinides strongly support the theoretical results. They suggest that a transition from the ground-$γ$ band coupling scheme to a scheme in which the ground band is situated in a separate irreducible representation of SU(3) should be realized towards the midshell regions. We propose that generally the SU(3) group contraction process should play an important role for such a kind of transitions in any collective band coupling scheme in heavy deformed nuclei.

nucl-th↗
arXiv1999

The 3-Dimensional q-Deformed Harmonic Oscillator and Magic Numbers of Alkali Metal Clusters

Magic numbers predicted by a 3-dimensional q-deformed harmonic oscillator with Uq(3) > SOq(3) symmetry are compared to experimental data for alkali metal clusters, as well as to theoretical predictions of jellium models, Woods--Saxon and wine bottle potentials, and to the classification scheme using the 3n+l pseudo quantum number. The 3-dimensional q-deformed harmonic oscillator correctly predicts all experimentally observed magic numbers up to 1500 (which is the expected limit of validity for theories based on the filling of electronic shells), thus indicating that Uq(3), which is a nonlinear extension of the U(3) symmetry of the spherical (3-dimensional isotropic) harmonic oscillator, is a good candidate for being the symmetry of systems of alkali metal clusters.

quant-ph↗
arXiv1997

Broken SU(3) symmetry in deformed even-even nuclei

A collective vector-boson model with broken SU(3) symmetry, in which the ground state band and the lowest $γ$ band belong to the same irreducible representation but are non-degenerate, is applied to several deformed even-even nuclei. The model description of ground and $γ$ bands together with the corresponding B(E2) transition probabilities is investigated within a broad range of SU(3) irreducible representations $(λ,μ)$. The calculations show that the $(λ,μ)$ characteristics of rotational nuclei depend to a great extent on the magnitude of the SU(3) splitting between the ground and $γ$ bands. It is found that for weakly split spectra, the ground--$γ$ band coupling scheme is realized relevantly within narrow regions of ``favored'' $(λ,μ)$ multiplets, while in the cases of strong splitting a description in which the ground band is situated alone in an irreducible representation is favored. The obtained results are analyzed in terms of the bandmixing interactions. The possibility for a transition between the different collective SU(3) schemes is discussed.

nucl-th↗
arXiv1997

Symmetries in nuclei and molecules

Recent progress in two different fronts is reported. First, the concept of bisection of a harmonic oscillator (HO) or hydrogen atom (HA), used in the past in establishing the connection between U(3) and O(4), is generalized into multisection (trisection, tetrasection, etc). It is then shown that all symmetries of the N-dim anisotropic HO with rational ratios of frequencies (RHO), some of which are underlying the structure of superdeformed and hyperdeformed nuclei, can be obtained from the U(N) symmetry of the corresponding isotropic HO with an appropriate combination of multisections. Furthermore, it is seen that bisections of the N-dim HA, which possesses an O(N+1) symmetry, lead to the U(N) symmetry, so that further multisections of the HA lead to the symmetries of the N-dim RHO. Second, it is shown that there is evidence that the recently observed in superdeformed nuclear bands $ΔI=4$ bifurcation is also occuring in rotational bands of diatomic molecules. In addition there is evidence that a $ΔI=8$ bifurcation, of the same order of magnitude as the $ΔI=4$ one, is observed in superdeformed nuclear bands and rotational bands of diatomic molecules.

nucl-th↗
arXiv1996

$ΔI=4$ and $ΔI=8$ bifurcations in rotational bands of diatomic molecules

It is shown that the recently observed $ΔI=4$ bifurcation seen in superdeformed nuclear bands is also occurring in rotational bands of diatomic molecules. In addition, signs of a $ΔI=8$ bifurcation, of the same order of magnitude as the $ΔI=4$ one, are observed both in superdeformed nuclear bands and rotational bands of diatomic molecules.

chem-ph↗
arXiv1996

Nuclear $β$- and $γ$- Collective Bands in the SU$_q$(2) Rotator Model

The SU$_q$(2) rotator model is used for describing the $β_1$- and $γ_1$-bands of even-even rare earth and actinide collective nuclei. Good results are obtained in nuclei with valence pair number $N>10$. It is shown that in the excited bands the violation of the exact SU(2) symmetry is generally stronger than in the ground state bands, indicating the presence of a nonadiabatic perturbation caused by the excited vibrational degrees of freedom. The physical content of the parameter $q$ is discussed. Predictions of the SU$_q$(2) model for B(E2) intraband transitions in excited bands are presented and the need for specific experimental data is pointed out.

nucl-th↗