Identification of yrast high-$K$ intrinsic states in ${}^{188}\mathrm{Os}$

The high-spin structure of the $Z=76$ nucleus ${}^{188}\mathrm{Os}$ has been studied using the incomplete fusion reaction ${}^7\mathrm{Li}+{}^{186}\mathrm{W}$. A $K^{\pi }={10}^{+}$ band has been established up to spin $({24}^{+})$ and its crossing with the ground-state band has been studied. In addition, intrinsic high-$K$ states have been identified and on top of two of them, $K^{\pi }=7^{-}$ and $K^{\pi }={10}^{-}$, regular bands have been observed. The $K^{\pi }={16}^{+}$ and $K^{\pi }={18}^{+}$ states are yrast whereas the $K^{\pi }={14}^{+}$ level lies only 33 keV above the yrast line and decays with a low reduced hindrance of $f_{\nu }<1.3$ to the ground-state band $(\Delta K=14)$. The results are discussed by means of a systematic comparison with the even-even neighboring nucleus ${}^{186}\mathrm{Os}$. Configuration-constrained multiquasiparticle potential-energy-surface calculations have been performed to identify the configurations of multiquasiparticle states.

Figure 1

Projections of the $\gamma \gamma$ matrices (a) without particle condition and requiring either a proton (b), a deuteron (c), or a triton (d) coincidence. The projection of the clean ${}^{188}\mathrm{Os}$ matrix is shown in (e). Peaks corresponding to transitions in ${}^{187}\mathrm{Ir}$, ${}^{188}\mathrm{Ir}$, ${}^{187}\mathrm{Os}$, ${}^{188}\mathrm{Os}$, and ${}^{189}\mathrm{Os}$ are labeled by symbols as indicated in the inset, respectively.

Figure 2

Level scheme of ${}^{188}\mathrm{Os}$ as established in the present work.

Figure 3

Coincidence spectrum with gate on the 686-keV ${12}^{+}\to {10}^{+}$ member of the gsb in the clean ${}^{188}\mathrm{Os}$ matrix.

Figure 4

Double-gated coincidence spectra with gates on (a) 582-keV and one of the 686-, 655-, or 575-keV transitions and on (b) 811-keV and one of the 686-, 655-, or 575-keV transitions; (c) single-gated coincidence spectrum with gate on the 503-keV transition.

Figure 5

Single-gated coincidence spectra with gate on the 589-keV (a) and 601-keV (b) transitions within the $K^{\pi }={10}^{-}$ band.

Figure 6

Time distributions observed for the 284-keV and the sum of the 390- and 729-keV $\gamma$ rays in prompt coincidence with the 314-keV ${11}^{-}\to {10}^{-}$ transition. Continuous lines represent the fits to the data points (see text for details).

Figure 7

Single-gated coincidence spectra with gate on the 262-keV ${16}^{+}\to {14}^{+}$ transition (a) and the 320-keV doublet (b).

Figure 8

Yrast line and high-$K$ multiquasiparticle (mpq) states in the even-even nuclei ${}^{182\text{−}188}\mathrm{Os}$.

Figure 9

Comparison between the ground-state bands (gsb), the $K^{\pi }={10}^{+}$ bands, and the $\gamma$ bands in ${}^{186}\mathrm{Os}$ (open symbols) and ${}^{188}\mathrm{Os}$ (filled symbols).

Figure 10

Alignment plot for the gsb–t band sequences in ${}^{184}\mathrm{Os}$ (squares),${}^{186}\mathrm{Os}$ (triangles), and ${}^{188}\mathrm{Os}$ (circles).

Figure 11

Experimental yrast and yrare levels within the ground-state band (filled circles) and the tilted $K^{\pi }={10}^{+}$ band (empty circles). The dashed lines indicate the unperturbed bands and the solid lines the yrast and yrare bands obtained in the two-band-mixing fit.

Figure 12

Calculated potential energy surfaces for the ground state (top left), the ${10}^{+}$ state (top right), the second ${14}^{+}$ state (bottom left), and the ${18}^{+}$ state (bottom right).