Lifetime measurements and shape coexistence in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi mathvariant="normal">Dy</mml:mi><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>144</mml:mn></mml:mrow></mml:mmultiscripts></mml:math>
Аннотация
The known level scheme of $^{144}\mathrm{Dy}$ has been extended and lifetime measurements have been made with the recoil-distance Doppler-shift method. Reduced transition probabilities and deformations have been determined for four low-lying transitions. These states form part of the first observed band crossing, giving information on the change in nuclear deformation resulting from the rearrangement of ${h}_{11/2}$ protons in the nucleus. Two bands built upon excited ${10}^{+}$ states have been assigned $\ensuremath{\pi}({h}_{11/2}){}^{2}$ prolate and $\ensuremath{\nu}({h}_{11/2}){}^{\ensuremath{-}2}$ oblate configurations with $\ensuremath{\tau}=12(2)\text{ps}$ and $0.01<\ensuremath{\tau}\ensuremath{\lesssim}16\text{ns}$, respectively. These long lifetimes are reasoned to be a result of shape coexistence at low energy and moderate spin. A known four-quasiparticle dipole band has been extended to higher spin and lifetime measurements suggest a long-lived bandhead state. In this case, the excited states in the band may be consistent with a shears model interpretation of a magnetic dipole rotor. However, the measured $B(M1)/B(E2)$ branching ratios reveal a larger than expected deformed rotational component compared with that in the analogous band in the lower mass isotone $^{142}\mathrm{Gd}$.
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