Discrete line gamma-ray spectroscopy in the (50-60)h spin domain of Er-161,Er-162 - art. no. 024321

Very high spin states (I=50-60 (h) over bar) have been observed in the tran sitional nuclei Er-161 and Er-162 using the Euroball gamma-ray spectrometer . In Er-161, three bands are observed well above spin 50 (h) over bar. In t he positive parity, positive signature (+, + 1/2) band a discontinuity in t he regular rotational behavior occurs at 109/2 (+) and a splitting into two branches occurs at 97/2(-) in the negative parity, positive signature (-, 1/2) band. The (-,- 1/2) band continues ina regular fashion to 115/2(-), t entatively (119/2(-)). In Er-162 the positive parity, even spin (+,0) yrast band is observed to continue smoothly up to 58(+) (60(+)) and the negative parity, even spin (-,0) and odd spin (-,1) bands are extended from 30(-) t o 34(-) and from 31(-) to 47(-) (49(-)), respectively. The high spin experi mental spectra are compared with both a simple model involving the occupati on of specific single neutron states in the absence of neutron pair correla tions and with more detailed cranked Nilsson-Strutinsky calculations in whi ch both proton and neutron pairing correlations are neglected. The very hig h spin domain is found to comprise a Series of unpaired rotational bands. U npaired bond crossings between bonds with different neutron and proton conf igurations are identified in Er-161. There is no evidence for aligned oblat e or terminating states being close to the yrast line in Er-161,Er-162 up t o spin approximate to 60 (h) over bar in contrast to the lighter Er isotope s.