Magnetic rotation and quasicollective structures in58Fe: Influence of theνg9/2orbital

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The structure of ${}^{58}$Fe was investigated at Gammasphere using ${}^{48}$Ca(${}^{13,14}$C,$x$$n$) fusion-evaporation reactions at a beam energy of 130 MeV. The level scheme has been revised and extended to $J\ensuremath{\sim}17\ensuremath{\hbar}$ and an excitation energy of 16.6 MeV. Regular band structures consisting of low-energy $\ensuremath{\Delta}J=1\ensuremath{\hbar}$ transitions have been observed at moderate spin ($J\ensuremath{\sim}8\ensuremath{\hbar}$--15$\ensuremath{\hbar}$) and are candidates for magnetic rotational bands. Self-consistent tilted-axis-cranking calculations within a relativistic mean-field theory were applied to investigate these bands and were found to reproduce the experimental results well. In other parts of the level scheme, quasirotational bands composed of stretched-$E2$ transitions have been extended to high spin, and other new bands have been identified. Positive-parity experimental states were compared to predictions of the spherical shell model using the GXPF1A, KB3G, and FPD6 effective interactions in the $fp$ model space. The projected shell model, with a deformed quasiparticle basis including the neutron $\ensuremath{\nu}{g}_{9/2}$ orbital, was applied to interpret regular $\ensuremath{\Delta}J=2\ensuremath{\hbar}$ band structures that extend beyond the maximum spin available for $\ensuremath{\pi}$[(${f}_{7/2}$)${}^{\ensuremath{-}2}$] $\ensuremath{\bigotimes}$ $\ensuremath{\nu}$[(${p}_{3/2}{f}_{5/2}{p}_{1/2}$)${}^{4}$] configurations and exhibit features characteristic of rotational alignment. It is clear that the $\ensuremath{\nu}{g}_{9/2}$ intruder orbital plays a crucial role in describing the quasirotational structures in this nucleus, even starting as low as $J\ensuremath{\sim}5\ensuremath{\hbar}$.