E1 transitions in rare earth nuclei and the SPDF boson model

Electric-dipole (E1) transitions between low-lying states of well deformed rare-earth nuclei are investigated using an SPDF boson model. The model can treat both the high-lying Giant Dipole Resonance (GDR) and the low-lying octupole vibrational bands. The p-boson is related to the GDR state while the f-boson is to the octupole vibration. The E1 operator T(E1) consists of p and f boson terms; the two p boson terms are determined by the experimental data on the GDR states. The remaining ƒ → d E1 transition charge is determined by fitting experimental B(E1) values between low-lying collective states. The present method has been applied to 156Gd, whose low-energy positive parity bands are well described by the SU(3) limit of IBM. It has been found that the E1 operator determined in this way gives the spin dependence of the B(E1) branching ratios close to the experimental results.