Shell-Model Study of Shears Bands in Light Pb Nuclei

Spherical shell-model calculations have been performed in the configuration space ( s_1/2h_9/2i_13/2)
and (p_1/2p_3/2f_5/2i_13/2) for protons and neutrons, respectively, in order to interpret the sequences of strong dipole transitions found in neutron-deficient Pb isotopes. Regular dipole bands are found if several high-j protons and high-j neutron holes are interacting with neutrons in the low-spin (fp) orbitals. The calculated B(M1) values are in the order of several µ_N ²
for the deltaJ=1 transitions, and the crossover E2 transitions are very weak. The mechanism generating the dipole bands is found to be the same as in the tilted axis cranking mean-field description.