Double giant dipole excitations in deformed nuclei

A calculation is presented for the excitation spectra of two superimposed dipole resonances for deformed nuclei by using theSU(3) limit of the interaction boson model for the case of many bosons. The results indicate that experiments to test the model may be feasible.     

Giant dipole resonance in heavy deformed nuclei

Analysis of all the experimental data on nuclear shape deformation and photonuclear reaction cross sections in the energy range of giant dipole resonance is performed. The relationship between the giant resonance width and the nuclear-quadrupole-deformation parameter value is shown.     

Studies of the electric dipole transition of deformed rare-earth nuclei

Spectrum and electric dipole transition rates and relative intensities in ^152–154Sm, ^156–160Gd, ^160–162Dy are studied in the framework of the interacting boson model with s,p,d,f, bosons. It is found that E1 transition data among the low-lying levels are in good agreement with the SU(3) dynamical symmetry of the spdf interacting boson model proposed by Engel and Iachello to describe collective rotation with octupole vibration. These results show that these nuclei have SU(3) dynamic symmetry to a good approximation. Also in this work many algebraic expressions for electric dipole transitions in the SU(3) limit of the spdf-IBM have been obtained. These formulae together with the formulae given previously exhaust nearly all the E1 transitions for low-lying negative parity states. They are useful in analyzing experimental data.     

gR and gK factors in deformed nuclei

The static and dynamic magnetic dipole moments of odd-mass and even-mass nuclei with 150R and intrinsic g-factors g_K.     

On collective two-phonon states in deformed nuclei

The centroid energies of the two-phonon states in doubly even deformed nuclei are calculated within the quasiparticle-phonon nuclear model taking into account the Pauli principle in the two-phonon components of the wave functions. It is shown that the collective two-phonon energies are shifted by 1–2 MeV to higher energies due to the Pauli principle. A strong fragmentation of the two-phonon collective states over many nuclear levels occurs at the excitation energies of 3–4 MeV. It is concluded that the two-phonon states cannot exist in deformed nuclei. The analysis of the available experimental data on the two-phonon states shows that the experimental data do not contradict the results of these calculations.     

On the shape of deformed nuclei

Shape observables measuring the intrinsic quadrupole deformation of the nucleus are identified. The consequences of these shape operators for the collective rotational and SU(3) models are derived. The operator measuring the square of the K quantum number is given.     

Excitation of multiple giant dipole resonances: from spherical to deformed nuclei

The effect of deformation on the excitation of multiple giant dipole resonances is studied. Analytical expressions are derived in the framework of the interacting boson model for the energies and E1 properties of giant dipole resonances in spherical and deformed nuclei, and a numerical treatment of transitional nuclei is proposed. Coulomb-excitation cross sections are calculated in ²³⁸U and in the samarium isotopes.     

On the isoscalar vibrations in axially deformed nuclei

Using the cranking model we show that the normal modes of isoscalar vibrations in axially deformed nuclei are essentially vibrations parallel and orthogonal to the symmetry axis. This leads to the fragmentation of the E0 and E2 giant resonance strengths in these nuclei.     

The single-nucleon form factor for knock-out and pick-up reactions in deformed nuclei

The single-nucleon form factor, or overlap integral, is a fundamental link between the nuclear structure and the reaction amplitude for knock-out or pick-up reactions. A formalism for calculating form factors between deformed nuclear states by means of angular momentum projection is presented. Intrinsic states are generated by the modified oscillator potential and refinements by isospin projection and an effective interaction are made. Results from applications to the reactions ¹⁶O(p, 2p)¹⁵N and ¹²C(p, 2p)¹¹B are presented.     

On the coupling between multiphonon configurations in deformed nuclei

The simplified microscopical multiphonon model (SMMM) convenient for the qualitative analysis of the interaction between multiphonon configurations in deformed nuclei is derived. The numerical estimates are given. The question on the low-lying two-phonon states in deformed nuclei is discussed.     

Electron form factors of deformable nuclei

Using the smallness of the deformation parameter of the nucleus, we obtain simple explicit expressions for the form factors of electroexcitation of the low-lying rotation-vibration states of light, deformable, even-even nuclei. The expressions satisfactorily describe the experimental data on the excitation of collective nuclear states by the inelastic scattering of fast electrons.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 62–66, September, 1987.     

Low energy orbital magnetic dipole excitations of heavy nonspherical nuclei

To clarify the physical nature of the orbital magnetic dipole excitations discussed widely in the past few years, a semiclassical model is presented and the nuclei¹⁵⁶Gd and¹⁶⁴Dy are investigated microscopically. The semi-classical model involves a consistent treatment of vibrational and rotational degrees of freedom; the microscopic results are obtained in quasiparticle-random-phase approximation (QRPA) with a realistic effective interaction. The results disagree with the picture of scissors modes or rotational vibrations.Dedicated to Prof. Dr. H.J. Mang on the occasion of his 60th birthday     

On allowed Gamow-Teller and first-forbidden β-decay in deformed nuclei

A method of evaluating strength functions in the RPA without actually solving the RPA equations is applied to Gamow-Teller β-decay. This method is numerically simpler than the conventional method and is the only practically possible procedure for more complicated applications. Further, we develop a method for solving the strength function (RPA) problem for an interaction which is a sum of several separable interactions. These two methods are then combined and, as an illustration, applied to first-forbidden β-decay.     

Orbital motion in deformed nuclei

Collective and microscopic properties of the low-lying, scissors-like, M1 excitations are studied. The collective features are analyzed in RPA using an energy-weighted M1 sum rule. Presented at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Electron scattering form factors for fp-shell nuclei

Elastic and inelastic electron-scattering form factors for multipolarities up to L = 7 and some transition-strength distributions are calculated with shell-model wave functions for about ten target nuclei in the mass range A = 52–62. The results are compared with the available measured transition strengths and (e, e') form factors.     

Pygmy dipole resonance in nuclei

A brief survey of the state of the modern microscopic theory of the so-called pygmy dipole resonance in nuclei is given—in particular, some unresolved problems are listed. It is emphasized that, in order to explain the pygmy dipole resonance, it is necessary but not sufficient to take into account the coupling of single-particle degrees of freedom to photon degrees of freedom. The results of the calculations performed for the first time for the isovector pygmy dipole resonance and the isovector electric giant dipole resonance in ¹²⁴Sn within a self-consistent approach involving, in addition to the standard quasiparticle random-phase approximation, a single-particle continuum and quasiparticle-phonon coupling of single-particle degrees of freedom to phonon degrees of freedom are presented. The results are found to be in satisfactory agreement with experimental data. The calculation of the isoscalar strength function in the energy region of the pygmy dipole resonance revealed that the nuclear-structure mechanism does not provide the isoscalar-strength suppression observed at energies in excess of 7 MeV in (α, α′γ) reactions; therefore, this suppression may stem from the reaction mechanism.