Shape isomerism at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>N</mml:mi><mml:mo>=</mml:mo><mml:mn>40</mml:mn></mml:mrow></mml:math>: Discovery of a proton intruder state in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi mathvariant="normal">Co</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>67</mml:mn></mml:mrow></mml:mmultiscripts></mml:math>
Abstract
The nuclear structure of $^{67}\mathrm{Co}$ has been investigated through $^{67}\mathrm{Fe}$ $\ensuremath{\beta}$ decay. The $^{67}\mathrm{Fe}$ isotopes were produced at the LISOL facility in proton-induced fission of $^{238}\mathrm{U}$ and selected using resonant laser ionization combined with mass separation. The application of a new correlation technique unambiguously revealed a $496(33)$ ms isomeric state in $^{67}\mathrm{Co}$ at an unexpected low energy of 492 keV. A $^{67}\mathrm{Co}$ level scheme was deduced. Proposed spin and parities suggest a spherical $(7/{2}^{\ensuremath{-}})$ $^{67}\mathrm{Co}$ ground state and a deformed first excited $(1/{2}^{\ensuremath{-}})$ state at 492 keV, interpreted as a proton 1p-2h prolate intruder state.
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