Doublet splitting in even-A deformed nuclei

The doublet splittings between excited two-quasiparticle states with parallel and antiparallel angular-momentum coupling in some even-A deformed rare earth nuclei have been calculated and compared with the experimental values. The influence of the various exchange forces is investigated, and results with both finite-range and zerorange forces are presented. Qualitative agreement is obtained when finite-range forces are used; but the SDI results—especially the spin-dependent ones—are also satisfactory if the states of the doublets are sufficiently pure two-quasiparticle states. This condition seems to be fulfilled by the doublet states considered in¹⁶²Dy, but not by those considered in the nuclei¹⁶⁸Er and¹⁷²Yb for which the experimental level splittings are rather large (about 450 keV) and could not reproduced at all. These discrepancies are discussed. It is argued that they are not due do the choice of the residual interactions but rather are due to configuration mixing, which is expected to be strong in these high-lying states.