Spin scissors mode and the fine structure of M1 states in nuclei

Abstract

30 pagesThe coupled dynamics of low lying modes, including the scissors mode, and various giant quadrupole resonances are studied with the help of the Wigner Function Moments method generalized to take into account spin degrees of freedom. Equations of motion for collective variables are derived on the basis of Time Dependent Hartree-Fock equations in the model of harmonic oscillator with spin orbital mean field potential plus quadrupole-quadrupole residual interaction. Introducing spin allows one to consider new types of nuclear collective motion where the nucleons with spin 'up' oscillate against nucleons with spin 'down'

Nuclear orbital and spin scissors with pairing

“…One of them, the nu-EPJ Web of Conferences 05007-p. 4 clear spin scissors, was described and studied in [10,11], where some indications on the experimental confirmation of its existence in actinides were discussed. Another phenomenon, the hidden angular momenta, is described in [12].…”

“…The most successful in the description of the energy and excitation probability of the scissors mode turned out the sum rule method [7] and RPA [8]. Very interesting qualitative features of the scissors mode were discovered with the help of Wigner Function Moments (WFM) method [9][10][11][12]. This method is a purely microscopic one, because it is based on the Time Dependent Hartree-Fock (TDHF) equation.…”

“…This method is a purely microscopic one, because it is based on the Time Dependent Hartree-Fock (TDHF) equation. In recent papers [10,11] the WFM method was applied for the first time to solve the TDHF equations including spin dynamics. The most remarkable result was the discovery of a new type of nuclear collective motion: rotational oscillations of "spin-up" nucleons with respect of "spin-down" nucleons (the spin scissors mode).…”

Nuclear scissors modes and hidden angular momenta

“…However, these expectations were not realised. It turned out that the spin-spin interaction does not change the general picture of the positions of excitations described in [15] favour of the spin scissors mode practically without changing their summed strength. One of the main points of this work was, indeed, that we were able to give a tentative explanation of a recent experimental finding [17] where the B(M1) values in 232 Th of the two low lying magnetic states are inverted in strength in favour of the lowest, i.e., the spin scissors mode, when cranking up the spin-spin interaction.…”

“…In a recent paper [15] the WFM method was applied for the first time to solve the TDHF equations including spin dynamics. As a first step, only the spin-orbit interaction was included in the consideration, as the most important one among all possible spin dependent interactions because it enters into the mean field.…”