Discrete line gamma-ray spectroscopy in the (50-60)h spin domain of Er-161,Er-162

J Simpson, A P Bagshaw, A Pipidis, M A Riley, M A Bentley, D M Cullen, P J Dagnall, G B Hagemann, S L King, R W Laird, J C Lisle, S Shepherd, A G Smith, S Tormanen, A V Afanasjev, I Ragnarsson

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    Very high spin states (I=50-60 (h) over bar) have been observed in the transitional 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 the positive parity, positive signature (+, + 1/2) band a discontinuity in the 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(-), tentatively (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(-) to 34(-) and from 31(-) to 47(-) (49(-)), respectively. The high spin experimental spectra are compared with both a simple model involving the occupation of specific single neutron states in the absence of neutron pair correlations and with more detailed cranked Nilsson-Strutinsky calculations in which both proton and neutron pairing correlations are neglected. The very high spin domain is found to comprise a Series of unpaired rotational bands. Unpaired bond crossings between bonds with different neutron and proton configurations are identified in Er-161. There is no evidence for aligned oblate or terminating states being close to the yrast line in Er-161,Er-162 up to spin approximate to 60 (h) over bar in contrast to the lighter Er isotopes.
    Original languageEnglish
    JournalPhysical Review C
    Issue number2
    Publication statusPublished - 2000


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