Relative population of oblate and prolate structures in189Au

High spin states of¹⁸⁹Au were populated via the¹⁷⁴Yb (¹⁹F, 4n reaction at 86, 90, 95 and 100 MeV beam energies. The study of the relative population of oblate and prolate structures shows a striking disappearance of the prolate band relative to the oblate ones as the beam energy goes from 86 to 100 MeV.     

On the coexistence of oblate and prolate deformed bands in83Zr

Deformation parameters of the positive parity yrast band and negative parity bands in⁸³Zr are deduced from lifetimes andE2/M1 mixing ratios. Lifetimes of high spin states have been determined from recoil distance Doppler shift and Doppler shift attenuation measurements using the⁵⁴Fe(³²S,2pnγ) ⁸³Zr reaction. Ten lifetimes and five lifetimes limits were determined. The positive parity band, built on theg _9/2 K=5/2 orbital has an average deformation ¦β ₂¦=0.28(2), and shows a reduction ofE2 transition strengths in the observed backbend region at I^π≈21/2⁺. In contrast, theE2 strengths in the negative parity states show a steady increase up to I^π≈=15/2^?. These states are more strongly deformed than the positive parity states (¦β ₂¦=0.33(3)). TheE2/M1 mixing ratios show that the negative parity band hasK=3/2 and is prolate, and favour oblate deformation for the positive parity yrast band. In theK=1/2^? band theE2 strength of the 7/2^?→3/2^? transition yields a deformation ¦β ₂¦=0.26(5). The band structure is compared with calculations within the Hartree-Fock Bogoliubov cranking model.     

Low-lying levels in 194Os and the prolate—oblate phase transition

Gamma-rays have been observed deexciting the 2⁺₁ and 2⁺₂ levels in ¹⁹⁴Os following two-fold neutron capture on ¹⁹²Os using the high-resolution bent crystal spectrometers and high neutron flux available at the ILL. The results indicate that rather different structural changes take place in the osmium and the platinum nuclei, and that the prolate-oblate transition occuring near ¹⁹²Os leads to a substantially developed oblate character in ¹⁹⁴Os.     

Spheres and prolate and oblate ellipsoids from an analytical solution of the spontaneous-curvature fluid-membrane model

An analytic solution for the Helfrich spontaneous curvature membrane model [H. Naito, M.Okuda, and Ou-Yang Zhong-Can, Phys. Rev. E 48, 2304 (1993); 54, 2816 (1996)], which has the conspicuous feature of representing a circular biconcave shape, is studied. Results show that the solution in fact describes a family of shapes, which can be classified as (i) a flat plane (trivial case), (ii) a sphere, (iii) a prolate ellipsoid, (iv) a capped cylinder, (v) an oblate ellipsoid, (vi) a circular biconcave shape, (vii) a self-intersecting inverted circular biconcave shape, and (viii) a self-intersecting nodoidlike cylinder. Among the closed shapes (ii)-(vii), a circular biconcave shape is the one with a minimum of local curvature energy.     

Effect of angular momentum projection in 28Si on the oblate and prolate alpha-cluster model state

Angular momentum projection is shown to diminish, but not resolve, the discrepancy between experiment and existing alpha-cluster model results for the oblate and prolate state in ²⁸Si.     

Shape coexistence at high spin in187Au

High-spin states in¹⁸⁷Au have been populated in the¹⁷²Yb(¹⁹F, 4n) reaction and studied with in-beam spectroscopic techniques using the “Château de Cristal” 4π-multidetector array. A comprehensive level scheme of¹⁸⁷Au has been established. Experimental band crossing frequencies and gains in alignment were deduced. Shape coexistence in¹⁸⁷Au, well established at low spin, is found to survive up to spin 57/2, and manifests itself through well separated oblate and prolate structures.     

Wetting layer and size effects on the nonlinear optical properties of semi oblate and prolate Si0.7Ge0.3/Si quantum dots

Semi oblate and semi prolate are among the most probable self-organized nanostructures shapes. The optoelectronic properties of such nanostructures are not just manipulated with the height and lateral size but also with the wetting layer element. The practical interest of derivatives of germanium and silicon has a great important role in optoelectronic devices. This study is a contribution to the analysis of linear and nonlinear optical properties of Si_0.7Ge_0.3/Si. In the framework of the effective mass approximation, we solve numerically the Schrödinger equation relative to one particle confined in Si_0.7Ge_0.3/Si semi prolate and semi oblate quantum dots by using the finite element method and by taking into consideration the effect of the wetting layer. The energy spectrum of the lowest states and the dipolar matrix for the fourth allowed transitions are determined and discussed. We also calculate the detailed optical properties, including absorption coefficients, refractive index changes, second and third harmonic generation as a function of the quantum dot sizes. We found that with the change in the size of prolate and oblate quantum dots, there is a shift in the resonance peaks for the absorption coefficient and refractive index. It is due to the modification in the energy levels with changing size. The study proves a redshift in the second harmonic generation and third harmonic generation coefficients with an increase in the height/radius of the oblate/prolate quantum dot, respectively. We also demonstrated the variation of wavefunction inside the quantum dot with the change in wetting layer thickness.     

Theoretical investigation of resonance frequencies in long wavelength electromagnetic wave scattering process from plasma prolate and oblate spheroids placed in a dielectric layer

Response of a prolate spheroid plasma and/or an oblate spheroid plasma in presence of long wavelength electromagnetic wave has been studied. The resonance frequencies of these objects are obtained and it is found that they reduce to the resonance frequency of spherical cold plasma. Moreover, the resonant frequencies of prolate spheroid plasma and oblate spheroid plasma covered by a dielectric are investigated as well. Furthermore, their dependency on dielectric permittivity and geometry dimensions is simulated.     

Relative Distribution of Au48 ～ Au52 in Au Plasma by Ionization Dynamics

The present work proposes a theoretical method called ionization dynamics to derive the ionic charge state distribution. Using relativistic quantum mechanics to calculate the energy level lifetime and average ionic lifetime of each ion, the first-order ionization rate constant can be obtained. Based on these data, from the solution of differential equations for consecutive-irreversible ionization reactions, one will be able to derive the ionic charge state distribution.The calculated average positive charge 49.24 of Au48 ～ Au52 and their relative distribution are in good agreement with the results of Lawrence Livermore National Laboratory.     

Electrical properties of Au–polystyrene–Au submicron structures

Received: 25 January 1998/Accepted: 28 May 1998     

Nuclear ground-state spin of185Au and magnetic moments of 187, 188Au: Further evidence for coexisting nuclear shapes in this mass region

Hyperfine structure measurements have been performed in some neutron-deficient gold isotopes, using on-line atomic-beam magnetic resonance (ABMR) techniques at the ISOLDE facility, CERN. The following results have been obtained: ¹⁸⁵Au, I = $\text{5}\text{2}$; ¹⁸⁷Au, Δv = 44.35(60) GHz, μ = 0.72(7) n.m. and ¹⁸⁸Au, Δv = ± 2992(30) MHz. A discussion of the influence of the hyperfine anomaly is included. With due regard to this effect, the magnetic moments of ¹⁸⁸Au may be given as μ = ± 0.07(3) n.m. The experimental data are compared with the results from calculations based on the particle-asymmetric rotor model. Strong evidence for coexisting nuclear shapes in ¹⁸⁵Au and for a much larger ground-state deformation in ¹⁸⁵Au than in ¹⁸⁷Au is presented.     

Coexisting oblate and strongly triaxial structures in <Superscript>191</Superscript>Pt

Excited states in ¹⁹¹Pt have been populated using the reaction ¹⁸⁶W + ¹¹B at 85MeV beam energy. Gamma-ray coincidences were measured using the EUROGAM-II spectrometer array. The level scheme has been extended considerably. Evidence for favoured structures of highly triaxial shape with -90^° coexisting with oblate structures has been obtained by comparison with total Routhian surface and cranked shell model calculations. The presence of proton excitations in both positive- and negative-parity states has been confirmed.     

Competition between (h11/2)2 proton and neutron excitations around128Ba: Coexistence of near prolate and near oblate shapes at high spin

Recent cranked shell model calculations give a possible explanation for the occurrence of two S-bands in Ba-nuclei.     

Nuclear spins of 186, 187, 188, 189, 189m Au

The nuclear spins of some neutron deficient gold isotopes have been measured using the atomic-beam magnetic resonance method. The following results have been obtained: ¹⁸⁶Au 10.7 min) I = 3, ${}^{187}\text{Au}\text{(8.5}\text{min}\text{) I =}\text{1}\text{2}$, ${}^{188}\text{Au}\text{(8.8}\text{min}\text{) I =}\text{1}\text{2}$, ${}^{189}\text{Au}\text{(28.3}\text{min}\text{) I =}\text{1}\text{2}$ and ${}^{\mathrm{<mtext>189</mtext><mtext>m</mtext>}}\text{Au}\text{(4.6}\text{min}\text{) I =}\text{11}\text{2}$. The spins of these typical transitional nuclei are discussed briefly in terms of various nuclear models.     

Influence of Au and TiO2 structures on hydrogen dissociation over TiO2/Au(100)

We performed H₂–D₂ exchange reactions over TiO_x/Au(100) and compared the observed reaction kinetics with those reported for TiO_x/Au(111) in order to clarify the influence of the Au and TiO₂ structures on dissociation of H₂ molecules. Low energy electron diffraction observations showed that the TiO₂ produced on Au(100) was disordered, in contrast to the comparatively ordered TiO₂ structure formed on Au(111). The activation energies and the turnover frequencies for HD formation over TiO₂/Au(100) agreed well with those for TiO₂/Au(111), clearly indicating that the hydrogen dissociation sites created over TiO₂/Au(100) were the perimeter interface between stoichiometric TiO₂ and Au, as was previously concluded for TiO₂/Au(111). We concluded that the creation of active sites for hydrogen dissociation was independent of the Au and TiO₂ structures consisting perimeter interface, and that local bonds that formed between Au and O atoms of stoichiometric TiO₂ were essential for the creation of active sites.