High precision quadrupole moment measurements of states up to I=20ħ in the yrast band of 158Er

The lifetimes of excited states in the yrast band in Er-158 up to I-pi = 20(+) have been measured to high precision by means of the Gammasphere spectrometer using the coincidence recoil distance technique. The reaction Sn-122(Ar-40,4n) at a beam energy of 185 MeV was used. The data were analyzed using the differential decay-curve method and transition quadrupole moments were extracted. The quadrupole moment was found to gradually increase by 15% of its 2(+) value before the first vi(13/2) alignment, after which it drops to a constant level 90% of the 2(+) value. Detailed comparisons are made with previous measurements and Ultimate Cranker calculations.