6533b859fe1ef96bd12b7683

RESEARCH PRODUCT

Discrete lineγ-ray spectroscopy in the(50–60)ħspin domain of161,162Er

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description

Very high spin states $(I=50--60\ensuremath{\Elzxh})$ have been observed in the transitional nuclei ${}^{161}\mathrm{Er}$ and ${}^{162}\mathrm{Er}$ using the Euroball $\ensuremath{\gamma}$-ray spectrometer. In ${}^{161}\mathrm{Er},$ three bands are observed well above spin $50\ensuremath{\Elzxh}.$ In the positive parity, positive signature $(+,+\frac{1}{2})$ band a discontinuity in the regular rotational behavior occurs at ${\frac{109}{2}}^{+}$ and a splitting into two branches occurs at ${\frac{97}{2}}^{\ensuremath{-}}$ in the negative parity, positive signature $(\ensuremath{-},+\frac{1}{2})$ band. The $(\ensuremath{-},\ensuremath{-}\frac{1}{2})$ band continues in a regular fashion to ${\frac{115}{2}}^{\ensuremath{-}},$ tentatively $({\frac{119}{2}}^{\ensuremath{-}}).$ In ${}^{162}\mathrm{Er}$ the positive parity, even spin (+,0) yrast band is observed to continue smoothly up to ${58}^{+}$ ${(60}^{+})$ and the negative parity, even spin $(\ensuremath{-},0)$ and odd spin $(\ensuremath{-},1)$ bands are extended from ${30}^{\ensuremath{-}}$ to ${34}^{\ensuremath{-}}$ and from ${31}^{\ensuremath{-}}$ to ${47}^{\ensuremath{-}}$ ${(49}^{\ensuremath{-}}),$ 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 band crossings between bands with different neutron and proton configurations are identified in ${}^{161}\mathrm{Er}.$ There is no evidence for aligned oblate or terminating states being close to the yrast line in ${}^{161,162}\mathrm{Er}$ up to spin $\ensuremath{\approx}60\ensuremath{\Elzxh}$ in contrast to the lighter Er isotopes.