6533b830fe1ef96bd1296f1e

RESEARCH PRODUCT

Microscopic description of low-lying two-phonon states: Electromagnetic transitions

subject

description

Microscopic description of low-lying two-phonon states in even-even nuclei is introduced. The main building blocks are the quasiparticle random-phase approximation (QRPA) phonons. A realistic microscopic nuclear Hamiltonian, based on the Bonn one-boson-exchange potential, is diagonalized in a basis containing one-phonon and two-phonon components, coupled to a given angular momentum and parity. The QRPA equations are directly used in deriving the equations of motion for the two-phonon states. The Pauli principle is taken into account by diagonalizing the metric matrix and discarding the zero-norm states. The electromagnetic transition matrix elements are derived in terms of the metric matrix. The model has been applied to the ${}^{106}\mathrm{Pd}$ and ${}^{108}\mathrm{Pd}$ nuclei, known to contain two-phonon structures. In spite of its simplicity, the model predicts energies and ratios of $B(E2)$ values in a reasonable agreement with the data.