Decay properties of very-high-spin states in transitional Er nuclei aroundA=154

Abstract

The 7 ray continuum structures of the transitional Er isotopes with A ~ 154 are studied using the reaction 74Ge(8r xn) lS8-XEr at El, b = 340 MeV. The measurements include energy spectra, total energies, multiplicities, angular distributions and lifetimes using the DSAM method. The analysis of data confirms the previously observed two-bump structure of the continuum radiation. A meticulous subtraction of discrete contributions proves the persistence of the low-energy bump even at high spins, i.e. I>40 h. The angular -distribution measurements assign predominant dipole structure to the bump at E~ =0.65 MeV, whereas the bump at E~ = 1.3 MeV is of almost pure quadrupole character at high spins. The lifetime measurements give evidence for a strong enhancement of the B(E2) values of the upper bump, B(E2)/Bsp>130. Spin-selection studies reveal, in the spin range I=30-50h an almost constant energy for the 1.3MeV bump, AE<60 keV.

Structure in theE2Quasicontinuum Spectrum ofDy154

“…However, the spectral shape and the extent of the quasicontinuum contribution were not known since discrete lines, which are largely responsible for structure in the total y spectra below 1 MeV, were not subtracted. For example, double bumps were observed in the total spectra of 154l55 Er, but the lower bump is drastically reduced after subtraction 13 of discrete lines, and the residuum has almost no E2 contribution, 13 when the average input spin decreases from 50h at a beam energy of 165 MeV to 36h at 148 MeV. These observations demonstrate that the transitions associated with the upper peak precede the ones giving rise to the lower peak.…”