2-OCTUPOLE-PHONON STATES IN PB-208

The so-called "two-octupole-phonon states" in Pb-208 are theoretically analyzed by using the Dyson boson mapping method for the collective multi-phonon space consisting of collective octupole phonons, collective quadrupole phonons and collective monopole pairing phonons. The effective hamiltonian used is constituted by a Woods-Saxon-type single-particle potential, monopole pairing forces for neutrons and protons, a quadrupole-quadrupole force and an octupole-octupole force. The numerical calculation reasonably reproduces the experimental low-energy spectrum and E2 and E3 transitions in Pb-208, and we can get a good understanding on the low-energy collective properties in Pb-208.