Semi-decoupled Bands Research Articles

High-spin levels inPt191andPt193and the triaxial rotor model

The high-spin level structures of the transitional nuclei /sup 191/Pt and /sup 193/Pt have been studied by (..cap alpha..,3n..gamma..) reactions on enriched Os targets. The measurements included ..gamma..-ray singles, comprehensive ..gamma..-..gamma.. coincidences, half-life determinations, and ..gamma..-ray angular distributions. The extensive /sup 191/Pt and /sup 193/Pt level schemes established are reported here. In both nuclei, decoupled ..nu..i/sub 13///sub 2/ /sup -1/ bands, strongly resembling the ground bands of the adjacent core nuclei, and many other high-spin positive parity states have been located. Low-lying 21/2/sup -/ bands have also been observed in both nuclei and they are described as semidecoupled bands with microscopic structures dominated by three-quasiparticle components of the type (..nu..i/sub 13///sub 2/ /sup -2/,..nu..j/sup -1/). The abundant information about ..nu..i/sub 13///sub 2/ level families obtained in these experiments and in a complementary /sup 191/Au decay study is discussed, and it is shown that these complex level spectra can be accounted for rather well in terms of the coupling of an i/sub 13///sub 2/ neutron hole to a triaxially deformed core. (AIP)

High-spin level structure ofPt190andPt192

The level structures of the shape transitional nuclei $^{190}\mathrm{Pt}$ and $^{192}\mathrm{Pt}$ have been studied by ($\ensuremath{\alpha},xn\ensuremath{\gamma}$) reactions on enriched Os targets. The measurements included $\ensuremath{\gamma}$-ray singles, prompt and delayed $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ conincidences, half-life determinations in the range 1-500 ns, and $\ensuremath{\gamma}$-ray angular distributions. Detailed level schemes for $^{190}\mathrm{Pt}$ and $^{192}\mathrm{Pt}$, incorporating much new spectroscopic information, are reported. Acute backbending observed at about spin 10 in the positive parity yrast sequences of the two nuclei is attributed to intersection of the ground bands by rotation aligned bands of both ($\ensuremath{\nu}i_{\frac{13}{2}}^{}{}_{}{}^{\ensuremath{-}2}$) and ($\ensuremath{\pi}h_{\frac{11}{2}}^{}{}_{}{}^{\ensuremath{-}2}$) character. A description of well-developed ${5}^{\ensuremath{-}}$ bands observed in both nuclei as semidecoupled ($\ensuremath{\nu}{i}_{\frac{13}{2}}, \ensuremath{\nu}$) bands is briefly discussed. ${10}^{\ensuremath{-}}$ isomers with half-lives of 47\ifmmode\pm\else\textpm\fi{}6 ns in $^{190}\mathrm{Pt}$ and 250\ifmmode\pm\else\textpm\fi{}30 ns in $^{192}\mathrm{Pt}$ are reported. The nature of these isomers is discussed in light of our related finding that the neighboring nuclei $^{189,\phantom{\rule{0ex}{0ex}}191,\phantom{\rule{0ex}{0ex}}193}\mathrm{Pt}$ have triaxial shapes ($\ensuremath{\gamma}\ensuremath{\sim}30\ifmmode^\circ\else\textdegree\fi{}$), and it is concluded that the ${10}^{\ensuremath{-}}$ states are predominantly of ($\ensuremath{\nu}{i}_{\frac{13}{2}}, \ensuremath{\nu}{h}_{\frac{9}{2}}$) two-quasiparticle composition.NUCLEAR REACTIONS $^{190,192}\mathrm{Os}(\ensuremath{\alpha},4n\ensuremath{\gamma})$, $^{188,190}\mathrm{Os}(\ensuremath{\alpha},2n\ensuremath{\gamma})$, $E=28\ensuremath{-}50$ MeV; measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}(\ensuremath{\theta})$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin, $\ensuremath{\gamma}\ensuremath{-}t$ relationships; $^{190,192}\mathrm{Pt}$ deduced level schemes, $J$, $\ensuremath{\pi}$, ${T}_{\frac{1}{2}}$.

Semi-decoupled bands in the even Hg isotopes

Abstract The odd-parity yrast states of the isotopes 190–200 Hg are studied in a model of two quasiparticles coupled to an oblate rotor and interacting by a surface delta interaction. The experimental energy spectra and the enhancement of E2 transition probabilities are well explained by the model. The pure Coriolis coupling problem (i.e., the problem obtained when the residual interaction is suppressed) is investigated in detail. It is shown that the main effect of the Coriolis force is to decouple the high-spin quasiparticle originating in the neutron 1 i 13 2 subshell from the system of the rotor and the low-spin quasiparticle. We study the coupling of a particle to an axially symmetric rotor, which has an intrinsic spin along its symmetry axis, and derive a good approximate solution to the problem.