A calculation of low-lying collective states in even-even nuclei

We present results of a calculation of the low-lying collective quadrupole states in even-even nuclei within the framework of the proton-neutron interacting boson model.     

Excited collective states of heavy even-even nuclei

Quadrupole-type collective excitations of even-even nuclei are analyzed. In this analysis, transverse γ vibrations of the nuclear surface are taken into account effectively, while longitudinal beta vibrations remain free. A potential energy of the exponential form is used for free surface longitudinal beta vibrations. The behavior of the energy levels of excited states in the ground-state, β, and γ bands of heavy nuclei is studied, and the predictive potential of the model used is demonstrated for transfermium nuclei.     

Properties of the low-lying excited states in even-even nuclei around the closed shell N=82

The properties of low-lying states in ¹³⁶Ba and ¹⁴⁴Nd are calculated within the quasiparticle phonon model. It is shown that the strong quadrupole interaction in the particle-particle channel leads to the appearance of low-lying isovector excitations. Due to this reason, there are two branches in the lowlying part of the spectrum, an isoscalar and an isovector one. Both branches show peculiar regularities of E2 and M1 transitions.     

Excited states of deformable even-even atomic nuclei

A method of calculating the collective excited states of even-even atomic nuclei is proposed. A formula depending on three parameters appropriate for calculating the energy ratios of the excited states of deformed and spherical nuclei as well as those in the intermediate region is obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 19–24, November, 1972.     

Theory of the excited states of deformable even-even nuclei

The excited states of nonspherical even-even nuclei are discussed taking the change in nuclear shape during excitation into account.     

On the description of collective negative parity bands in even-even deformed nuclei

The collective bands of negative parity are studied via a microscopic approach where Coriolis forces and octupole correlations are treated on an equal footing. The apparent moment of inertia of these bands are nicely reproduced.     

Studies of low-lying states of even-even Xe isotopes within the nucleon pair approximation

We study the relevance of nucleon pairs with higher spins, in addition to spin-zero and spin-two pairs (i.e., SD pairs), in low-lying states of even-even Xe nuclei. By including those higher-spin pairs in our configuration, we recalculate energy level schemes, electrical quadrupole moments, magnetic moments and electric quadrupole transition rates, for low-lying states of even-even ^128–142Xe nuclei. The agreement between our calculated results and the experimental data is substantially improved in comparison with previous studies.     

Studies of low-lying states of even-even Xe isotopes within the nucleon pair approximation

We study the relevance of nucleon pairs with higher spins, in addition to spin-zero and spin-two pairs (i.e., S D pairs), in low-lying states of even-even Xe nuclei. By including those higher-spin pairs in our configuration, we recalculate energy level schemes, elec trical quadrupole moments, magnetic moments and electric quadrupole transition rates, for low-lying states of even-even 128-142Xe nuclei. The agreement between our calculated results and the experimental data is substantially improved in compari...     

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.     

Effect of low-lying collective states on the structure of giant resonances

The influence of coupling of the usual particle-hole states to particle-hole states built on a collective state has been estimated. Numerical calculations are performed for Ni⁶⁰Zr⁹⁰ and²⁰⁸Pb.     

Transition probabilities and static moments of excited states in even-even nuclei

A new approach is made to calculate the generalized single-particle density matrixp ^μv in even-even nuclei. It is shown that this quantity is included in the three particle response function, for which we derived a renormalized equation. Taking into account in a consequent way the effective particle-hole interaction we received a formula for the static moment of excited states and the transition probability between such states which is essentially different from the usual RPA theory.     

A shell-model description of 0+ intruder states in even-even nuclei

Starting from the nuclear shell structure in medium-heavy and heavy nuclei, the excitation energy for low-lying 0⁺ intruder states is studied. Taking as a simplified model two particle-two hole (2p-2h) excitations across closed shells, the effects of the pairing and the proton-neutron (monopole and quadrupole component) residual interaction on the unperturbed energies are calculated. Application to major closed-shell (fZ = 50, Z = 82) and to subshell (Z = 40, Z = 64) regions is performed. We especially concentrate on 0⁺ intruder states in the even-even Pb nuclei.     

Transition charge densities of low-lying collective states in even Zn isotopes

The inelastic electron scattering cross sections for the quadrupole transitions to the 2₁⁺ and 2₂⁺ states in the even Zn isotopes ⁶⁴Zn, ⁶⁶Zn and ⁶⁸Zn and for the hexadecapole transition to the 4⁺₁ state in ⁶⁴Zn have been measured in a momentum transfer range up to q = 2.2 fm^?1. In the frame-work of the vibrational model these states are considered as one- and two-quadrupole-phonon states. The measurements are characterized by high statistical accuracy and by an overall resolution of δE/E₀ = 10^?3 which permitted separation of almost all members of the two-phonon triplet. The measured cross sections are analyzed with phenomenological models as well as with a Fourier-Bessel expansion of the transition charge density. The latter analysis yields realistic error bands for the transition charge densities and model-independent values for the reduced transition probabilities and transition radii.     

Magnetic moments of low-lying states in medium weight odd nuclei

The magnetic moments of several short-lived states in¹⁰³Rh,^1111113Cd and^1231125Te isotopes have been measured by the transient field technique. The results, together with those obtained earlier in the^1071109Ag isotopes, have been compared to predictions of various models and calculations. In the Z=45, 47 isotopes, the odd proton seems to deform the vibrational core. The data are best explained within the framework of a triaxially deformed nucleus. In the odd neutron isotopes with 50<N<82, and Z=48, 52, weak coupling states coexist with single particle states in a mix of configurations.     

A method of angular momentum projection for excited states in even-even nuclei

A method of angular momentum projection for the excited states in even-even nuclei is formulated within the framework of the Hartree-Bogoliubov theory. A preliminary application of this method is performed for the K=0^? band in ¹⁶²Er.     

Electron scattering studies of low-lying collective states of even Zn isotopes

The inelastic electron scattering cross sections for the excitation of the low-lying collective states in the even Zn isotopes ⁶⁴Zn, ⁶⁶Zn, ⁶⁸Zn and ⁷⁰Zn have been measured in the momentum transfer region q = 0.3–1.1 fm^?1. Strong transitions to the first 2⁺ and 3^? states have been observed and the modified Tassie model with a two parameter Fermi charge distribution for the ground state was used to extract the values for the reduced transition probability B↑ (Eλ). Besides the investigation of these states, which in the framework of the vibrational model are considered as one-phonon states, special effort was made to measure the transition to the 2⁺ two-phonon states in ⁶⁴Zn (ε = 1.80 MeV) and ⁷⁰Zn (ε = 1.76 MeV). We have applied the anharmonic vibrator model to these two nuclei and have extracted values for the static quadrupole moment of the first excited state.     

Study of low-lying collective states using a Microscopic Anharmonic Vibrator Approach

Anharmonic features of the low-lying collective states in the ruthenium isotopes have been investigated systematically by using the Microscopic Anharmonic Vibrator Approach (MAVA). MAVA is based on a realistic microscopic G-matrix Hamiltonian, only slightly renormalized in the adopted large realistic single-particle spaces. This Hamiltonian is used to derive equations of motion for the mixing of one-and two-phonon degrees of freedom starting from collective phonons of the quasiparticle random-phase approximation. Interesting applications to analysis of double-beta-decay rates to excited collective states are foreseen. Presented by J. Suhonen at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September 26–29, 2005.     

Boson structure of the low-lying states of 1p0f-shell nuclei

The boson structure of the low-lying states of A = 44 and A = 60 nuclei is investigated by studying the eigenvalue problem of the boson image of the shell-model Hamiltonian in spaces expanded in terms of bosons corresponding to the collective nuclear pairs allowed in the 1p0f shell. The text was submitted by the authors in English.