Microscopic treatment of the coupled monopole and quadrupole vibrations in light nuclei

The coupled monopole and volume-conserving quadrupole oscillations in ⁴He, ¹²C, ¹⁶O, ²⁰Ne and ⁴⁰Ca have been studied within the framework of the Hill-Wheeler generator coordinate method.     

Elasticity and quadrupole vibrations

Coherent quadrupole vibrations are shown to obey the classical equations for an elastic medium. The motion is predominantly a transverse wave.     

Alpha-particle superfluid bands in nuclei

The systematics of α-particle separation energy is studied from the point of view of pairing-rotational structure. Two mass regions are identified where collective pairing bands can exist. The moment of these bands is compared with linear sums of (n-n) and (p-p) bands and an increase in collectivity of factor 10 is deduced.     

The low-lying quadrupole collective excitations of Ru and Pd isotopes

Quadrupole excitations of even-even Ru and Pd isotopes are described within a microscopic approach based on the general collective Bohr model which includes the effect of coupling with the pairing vibrations. The excitation energies and E2 transition probabilities observed in ^104–114Ru and ^106–110Pd are reproduced in the frame of the calculation containing no free parameters. Particularly interesting are ¹⁰⁴Ru and ^106–110Pd where good agreement to very rich information based on Coulomb excitation experiments is achieved.     

Effects of proton pair vibrations in the low-lying spectrum of closed-shell nuclei: Structure of 48Ca

The importance of proton pair vibrations in the low-lying spectra of closed-shell nuclei with Z ≠ N is emphasized. Indications for the occurrence of these states in ⁴⁸Ca are obtained from a restricted shell-model calculation with both active neutrons and protons.     

Octupole vibrations of deformed nuclei

The octupole vibrations of deformed nuclei are studied. A strong coupling between the harmonic octupole vibrations and the quadrupole ellipsoid is assumed. This interaction gives rise to a splitting of octupole bands with different projection quantum numberK. TheE1-transitions of the octupole states are explained within the frame of the Dynamic Collective Theory ofDanos andGreiner by calculating the Coulomb interaction between octupole vibrations and giant resonances. Furthermore, theE2- andE3-transitions of the octupole states are studied. The spectrum of W¹⁸² is investigated in detail. A fair agreement between theory and experiment is obtained. Predictions for the octupole spectra of Sm¹⁵² and Gd¹⁵⁶ are given.     

Energy density functional approach to superfluid nuclei

We show that, within the framework of a simple local nuclear energy density functional (EDF), one can describe accurately the one- and two-nucleon separation energies of semimagic nuclei. While for the normal part of the EDF we use previously suggested parametrizations, for the superfluid part of the EDF we use the simplest possible local form compatible with known nuclear symmetries.     

Static electric quadrupole and hexadecapole moments of nuclei

Ground-state static electric quadrupole and hexadecapole moments of even nuclei are calculated microscopically. Rare-earth, actinide and neutron-deficient nuclei with 50 <Z, N < 82 and neutron-rich nuclei with 28 < Z < 50, 50 < N < 82 are studied. Fairly good agreement with experiment is found. In the actinide region, the electric moments of fission isomers are also examined.     

Monopole vibrations of closed shell nuclei

A collective vibration in normal Fermi systems is described which represents the formation of virtual Cooper pairs and is closely connected with the phase transition from the normal to the superfluid state. Numerical results for this collective mode in O¹⁶ are reported and compared with experimental data on the 6.06 MeV 0⁺ level.     

Current electric quadrupole moments of atoms and nuclei

It is shown that current electric multipoles exist. Their field is electrostatic and it is unrelated to the existence of a net electric charge. At long range, it is the same as the field of the corresponding charge electric multipoles. Current electric multipoles arise during the motion of magnetic multipoles. An orbital motion of magnetic dipoles, a precession of a current-carrying loop, and the motion of magnetic quadrupoles all lead to current electric quadrupole moments. Expressions for the current electric quadrupole moments of atoms and nuclei are derived.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 53–58, July, 1991.The author wishes to thank S. A. Kuten' and V. I. Rapoport for useful comments offered during the writing of this paper and for a discussion of the results.     

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.     

Effect of pairing correlation on low-lying quadrupole states in Sn isotopes

We examined the low-lying quadrupole states in Sn isotopes in the framework of fully self-consistent Hartree-Fock+BCS plus QRPA.We focus on the effect of the density-dependence of pairing interaction on the properties of the low-lying quadrupole state.The SLy5 Skyrme interaction with surface,mixed,and volume pairings is employed in the calculations,respectively.We find that the excitation energies and the corresponding reduced electric transition probabilities of the first 2~+ state are different,given by the three pairing interactions.The properties of the quasiparticle state,two-quasiparticle excitation energy,reduced transition amplitude,and transition densities in~(112)Sn are analyzed in detail.Two different mechanisms,the static and dynamical effects,of the pairing correlation are also discussed.The results show that the surface,mixed,and volume pairings indeed affect the properties of the first 2~+ state in the Sn isotopes.     

Photofission of nuclei with allowance for wriggling vibrations of fissioning nuclei

It is confirmed that one source of the large relative orbital momenta L of fragments in spontaneous and stimulated low-energy nuclear fission is quantum transverse zero-point wriggling vibrations of the fissioning system near its scission point. The angular distributions of fragments of low-energy photofission of actinide nuclei, calculated using the quantum theory of fission, are compared. Vibrations are allowed for by using parameter C _w determined by Nix and Swiatecki. Agreement between the experimental and theoretical angular distributions for ²³⁴U, ²³⁶U, ²³⁸U, ²³⁸Pu, ²⁴⁰Pu, ²⁴²Pu nuclei is observed. The strong sensitivity of the theoretical angular distributions for ²³⁸Pu, ²⁴⁰Pu, ²⁴²Pu nuclei toward the choice of parameters of transient fissioning states at the external and internal fission barriers is demonstrated.     

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.