Discovery of a 10<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>μ</mml:mi></mml:mrow></mml:math>s isomeric state in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow/><mml:mrow><mml:mn>63</mml:mn></mml:mrow><mml:mrow><mml:mn>139</mml:mn></mml:mrow></mml:msubsup></mml:mrow></mml:math>Eu
Аннотация
Recoil-isomer tagging with the $^{54}\mathrm{Fe}$$+$$^{92}\mathrm{Mo}$ reaction was used to establish a 10(2)-$\ensuremath{\mu}$s isomeric state in $^{139}\mathrm{Eu}$. Prompt versus delayed $\ensuremath{\gamma}$-ray coincidence data have revealed the presence of a prompt rotational band built upon the isomer. The alignment properties of the states in this band show that the isomer is based upon a proton ${g}_{7/2}$ configuration. The decay of the isomer takes place through a single 26-keV $E1$ transition. The $\ensuremath{\gamma}$-ray transition strength for this decay is consistent with those established in the neighboring isomeric gamma-soft nuclei. In these nuclei, isomers are expected to form as a consequence of differences in nuclear shapes or configurations, and the natural hindrance associated with configuration-changing $E1$ transitions. The isomeric nature of the state in $^{139}\mathrm{Eu}$ is reasoned to be because of difference in shape of the proton ${g}_{7/2}$ state and the proton ${h}_{11/2}$ ground state to which it decays.