Fragmentation Of One-phonon States Research Articles

DESCRIPTION OF E1 TRANSITION IN DOUBLY EVEN WELL-DEFORMED NUCLEI

One-phonon states with Kπ=0− and 1− are calculated within the RPA taking the isoscalar and isovector particle-hole and particle-particle octupole and isovector particlehole dipole interactions into account. General equations of the Quasiparticle-Phonon Nuclear Model are modified. The energies and wave functions of the nonrotational states below 2.3 MeV in 160Gd calculated within this model are in good overall agreement with experimental data. The E1 transition rates in several doubly even well-deformed nuclei are calculated. The influence of the radial dependence of the dipole and octupole interactions on E1 and E3 transition probabilities is investigated. It is shown that the fragmentation of one-phonon states below 2.3 MeV weakly affects the E1 transition rates from 1− states to the ground state. The fragmentation of one- and two-phonon states strongly affect B(E1) values of the transitions from 1− states with energy above 2.5 MeV to the ground states and between excited states. The results of calculating the E1 transition rates are compared with the relevant experimental data.

Fragmentation of the Gamow-Teller resonance in spherical nuclei

The fragmentation of one-phonon states describing the Gamow-Teller (GT) resonance in 90Zr, 120,124Sn, 124Te, 140Ce and 208Pb is calculated within the quasi-particle-phonon nuclear model. The GT strength is distributed over three regions: the low-energy region, the region of the resonance maximum and the high-energy region. The quasiparticle-photon interaction shifts 10-30% of the GT strength from the resonance region towards higher excitation energies. As a result, 40-60% of the sum-rule limit 3(N-Z) remains in the region of the maximum of the GT resonance. The low-energy region contains 15-30% of 3(N-Z). The fragmentation of one-photon charge-exchange states is thought to be one of the reasons for the quenching of the GT strength in the region of its maximum.

Nuclear properties in the lead region within the quasiparticle-phonon nuclear model

The properties of the low-lying states and giant resonances in 208Pb are calculated within the quasiparticle-phonon nuclear model, the model parameters being fixed. The fragmentation of the deep hole states 1 h 11 2 , 1 g 7 2 and 1 g 9 2 in 207Pb and 1 g 7 2 , 1 g 9 2 , 2 p 1 2 and 2 p 3 2 in 203, 205, 207Tl is calculated, and qualitative agreement with the available experimental data is obtained. The s-, p- and d-wave neutron strength functions are calculated for 206Pb + n and 207Pb + n resonances. Their energy dependence is correctly described up to 0.9 MeV above the neutron binding energy B n. The reduced E1 transition probabilities and the total photoabsorption cross sections σ γt in 206, 208Pb are calculated. It is shown that substructures observed in the energy dependence σ γt are caused by the fragmentation of one-phonon states. A fine structure of the isoscalar quadrupole resonance is explained, and the description of the LEOR and HEOR in 208Pb is obtained, which is in agreement with the experimental data.

Fragmentation of giant multipole resonances over two-phonon states in spherical nuclei

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(E λ, 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.