THE ORIGIN AND DISTRIBUTION OF THE E1 STRENGTH OVER LOW-LYING STATES IN WELL-DEFORMED NUCLEI

The energies and wave functions of the K(pi) = 0- and 1- states in Gd- 158, Dy-162, Dy-164, and Er-168 are calculated in the RPA, taking the isoscalar and isovector particle-hole and particle-particle octupole a nd isovector particle-hole dipole interactions into account. It is sho wn that the inclusion of the isovector dipole interaction in addition to the octupole interactions leads to the shift of the largest part of the E1 strength from low-lying states to the GDR. The origin of the E 1 strength in the low-energy region is explained as an effect of the q uadrupole equilibrium deformation and isoscalar octupole and isovector dipole interactions. At excitation energies below 4 MeV, the total E1 strength for K(pi) = 0 states is 3 to 4 times as large as that for th e K(pi) = 1- states. The fragmentation of the one-phonon K(pi) = 0- an d 1- states in Dy-164 and Er-168 due to coupling with the two-phonon c onfiguration is calculation. The B(E1) values for the first K(nu)pi = 0(1)- states are 3 - 5 times as large as the experimental values. The concentration of the E1 strength over the K(pi) = 0- states at energie s 2.6 - 3.5 MeV in Er-168 and 3.6 - 3.9 MeV in Dy-164 is predicted.