IDENTIFICATION OF ROTATIONAL BANDS AT INTERMEDIATE EXCITATION IN ER-168

A study of the levels in Er-168, initially reported on in 1981, has been concluded. The original neutron capture data have been supplemented with data from a new series of measurements taken with improved statistics, derived from curved-crystal measurements of selected portions of the gamma-ray spectrum as well as from a measurement of gamma-rays in the range 1300 keV less-than-or-equal-to E-gamma less-than-or-equal-to 2300 keV using an intrinsic Ge spectrometer. These new data have led to the establishment of an improved gamma-ray line list which, in turn, has led to more definitive multipolarity information from existing conversion electron data. Using these data, employing the Ritz combination principle in conjunction with knowledge of the location of levels in Er-168 derived from a series of particle transfer experiments, a comprehensive level scheme was constructed where 128 levels are arranged into 33 rotational bands as well as four isolated bandheads. This detailed information about the levels, their radiative decay, their spin-parity assignments and their grouping into rotational bands constitutes an ideal experimentally-based testing ground against which the predictions of theoretical models of low-lying collective excitations in heavy nuclei can be compared.