V.G. Soloviev

Equilibrium deformations of neutron-rich nuclei in the A ≈ 100 region

Ground state equilibrium deformations, deformation energies and quadrupole moments are calculated for even nuclei in the 28 < Z < 50, 50 < N 82 region. It is found that the equilibrium shapes of these nuclei are axially symmetric For most of them the oblate shapes are preferred. All nuclei in the investigated region seem to be soft against both beta and gamma deformations

Ground and excited state deformations in the 50 < Z, N < 82 region

The dependence of the ground-state energy on beta and gamma deformations for neutron-deficient nuclei with 50 < Z, N < 82 is studied. Even, odd and doubly odd nuclei are investigated. The equilibrium deformations and the deformation energies are calculated. It is found that the energy minimum occurs at axially symmetric shapes, either oblate (γ = 60°) or prolate (γ = 0°). As a function of the beta deformation, the energy has two minima, as a rule close in energy; one for positive and the other for negative value of beta. When going via gamma deformation no significant barrier between the two minima is found, suggesting a softness of the nuclei to gamma deformation. Quasi-particle excited states are also studied. A possibility for shape isomers is obtained.

Quasi-particle and collective structure of the states of even, strongly-deformed nuclei

Abstract The structure of the non-rotational excited states of even, deformed nuclei in the ranges 150≦ A ≦ 186 and 228 ≦ A ≦ 254 is investigated. The energies of the first and second Kπ = 2+ and 0+ states are calculated taking into account the blocking effect in the framework of the method of approximate second quantization. These energies agree sufficiently well with the corresponding experimental data. The structure of the excited states is investigated and it is found that in most cases the lowest lying Kπ = 2+, 0+ states possess clearly expressed collective properties. In some cases the energies of quadrupole excited states lie near the secular equation poles and the structure of Kπ = 2+ states is similar to the two-quasi-particle ones. The particularities of the Kπ = 0+ states are investigated. The spectroscopic factors are calculated for direct nuclear reactions and the relative probabilities are found for beta transitions to the Kπ = 0+ states. A satisfactory agreement is obtained between theory and experiment. The role of the F and Q forbiddennesses in the superfluid nuclear model is investigated.

Energies of strongly deformed even nuclei in the range 228 ≦ A ≦ 254

Abstract The energies of the two-quasi particle excited states of even nuclei in the range 228 ≦ A ≦ 254 are calculated. The obtained energies of some collective non-rotational excited states and those of two-quasi-particle neutron and proton states up to 2 MeV are tabulated. Data on the structure of gamma vibrational and octupole states are given. It is shown which states must be described as two-quasi-particle states and which take part in the formation of collective states.

Structure of the ground and excited states of odd-mass deformed nuclei in the region 153 ≦ A ≦ 187

Abstract The interactions of quasi-particles with quadrupole and octupole phonons in deformed odd-mass nuclei are considered in the framework of the method of approximate second quantization. The properties of phonons are determined in investigating even-mass nuclei. In considering the interaction of quasi-particles with phonons in odd-mass nuclei, there is therefore not a single free parameter. The peculiarities of the secular equations are studied and it is shown that for many states, besides the interaction of quasi-particles with gamma-vibrational phonons, the interactions of quasi-particles with octupole and beta-vibrational phonons are very important. The energies and wave functions for the majority of odd-mass nuclei in the range 151 ≦ A ≦ 187 are found. It is shown that the interaction of quasi-particles with ohonons leads to the appearance of admixtures to the one-quasi-particle states and improves the description of these states as compared to the independent quasi-particle model. It is shown that this interaction leads to the formation of the collective non-rotational states and of the complex structure states in odd-mass nuclei. The calculated energies of the excited states, values of B (E2), the decoupling parameters a and the spectroscopic factors agree rather well with the corresponding experimental data. It is concluded that the interaction of quasi-particles with phonons gives a correct description of the structure of the ground and excited states of deformed odd-mass nuclei.

FRAGMENTATION OF GIANT MULTIPOLE RESONANCES OVER TWO-PHONON STATES IN SPHERICAL NUCLEI

Abstract A method for the calculation of the strength function photoexcitation of giant multipole resonances in spherical nuclei is presented. The method is developed in the framework of the model based on the quasiparticle-phonon interaction. The one-phonon states are calculated in the random phase approximation. The fragmentation of one-phonon states over two-phonon ones is calculated. The strength function b(Eλ, η) and the positions of giant isovector dipole and isoscalar quadrupole resonances in 90Zr, 120Sn and 124Te are found. The calculations of the transition strengths and positions of these resonances are in reasonable agreement with experiment. The strength function b(E2, η) is calculated for the isovector quadrupole resonance in 90Zr. The description of the lowenerev octupole resonances in 90Zr and 120Sn is in agreement with experiment.

Single-particle energies and wave functions for the saxon-woods potential and the levels of odd-A nuclei in the actinide region

Abstract The Saxon-Woods single-particle energies and wave functions are given for the description of deformed nuclei in the region 234 ≦ A ≦ 250. The energies and the wave functions for the non-rotational states of odd- A nuclei are calculated taking into account the interaction of quasiparticles with phonons. The latter is found to be more important for nuclei in the actinide region than in the rare-earth one. A rather good description of the energies of low-lying non-rotational states in 235 U, 237 U, 241 Pu, 245 Cm, 247 Cm, 249 Cm, 237 Np, 241 Am and 249 Bk is obtained. The calculated Saxon-Woods single-particle energies and wave functions may serve as a basis for calculating various characteristics of nuclei in the actinide region.

Gamow-teller β+ decays and strength functions of (n,p) transitions in spherical nuclei

Abstract The effect of the particle-particle interaction on the Gamow-Teller β + decay and strength functions of (n, p) transitions is studied. The integrated log ft values for the GT decays of 152 Yb, 152,150 Er, 146,148 Dy and 96 Pd are calculated in the RPA with separable particle-hole and particleparticle interactions. A good description of log Ft is obtained with the constants χ(s01) 1 = −23 A MeV and G 01 1 = 7.5/ AMeV at ¦g A /g v ¦=1 and G 01 1 = 7.9/ AMeV at| g A / g v v | = 1.25. experimental data on β + decays of nuclei far from stability one cannot conclude that the weak axial-vector constant g A is strongly renormalised in nuclei. The particle-particle interaction is shown to influence strongly the total strength S + of (n, p) transitions by diminishing it (1.5–3.0) times. For the reaction 54 Fe(n, p) 54 at forward angles the calculated value S + = 4.2 is in agreement with the experimental one.

The description of the fragmentation of one-quasiparticle states in spherical nuclei

Abstract The fragmentation of hole states in spherical nuclei is calculated within the quasiparticlephonon nuclear model. The model equations and the numerical method for their solution are given. The influence of the “quasiparticle plus two phonon” components of the wave function and of phonons of different multipolarity on the fragmentation of one-quasiparticle states is investigated. The necessity of taking into account the “quasiparticle plus two phonon” components and of calculating with a large phonon basis is shown. The calculated values of the centroid E x , width Γ ↓ and spectroscopic factor S j , are in satisfactory agreement with the experimental data for the fragmentation of the neutron states 1 d 3 2 and 1f 7 2 in 57 Ni, 1g 9 2 in Sn and 123 Te, and of the proton state 1g 9 2 in 143 Pm, etc. The calculated strength concentration of the lg 9 2 state decreases in the peak when passing from 115 Sn to 119 Sn. However, this decrease is less than that observed experimentally.

Magnetic quadrupole resonance in spherical nuclei

Abstract The distribution of the M2 strength in spherical nuclei is studied within the quasiparticle-phonon nuclear model. It is shown that the interaction of the one- and two-phonon states affects strongly this distribution at the excitation energies E x > 15 MeV. In all the nuclei the strength of the M2 transitions is concentrated in the excitation energy region of 6–12 MeV. At these energies the calculated total value of B (M2)↑ is in good agreement with the experimental data in 90 Zr and 208 Pb. The calculations show that a group of states observed in 58 Ni at an energy of about 7 MeV in the (e, e′) experiments is a part of the M2 resonance.