High-resolution study of 166Er with the (p, t) reaction

Excited states in the deformed nucleus Er-166 have been studied with high-energy resolution in the (p, t) reaction, with the Munich Q3D spectrograph. 143 states have been observed up to 4 MeV excitation, and spin and parity has been proposed for about 100 states, based on a DWBA analysis of their angular distributions, out of which 11 are excited 0(+) states, and 39 2(+) states. The excitation pattern of these states (especially the 0(+) ones) in Er-166 is compared to that in Er-168. Calculations were carried out with the spdf-IBM model, which gives a reasonable agreement with the observed number of 0(+) states in Er-166 and their excitation in the (p, t) reaction. The 2n-transfer intensity pattern for the 0(+) states in the Er-166(t, p)Er-168 reaction is also reasonably predicted. However, the spdf-IBM calculations do not explain the differences between Er-166 and Er-168, in the (p, t) transfer distribution of the 0(+) states. The understanding of these differences, which appear to be related to a structure change at the N = 98 deformed subshell closure, remains as an important issue of future, more elaborated model calculations.