Proton Orbital [541]1/2 and Backbending in 178W

The microscopic mechanism of nine experimentally observed bands in ^178W is investigated using the particle-number conserving method of the cranked shell model with monopole and quadrupole paring interactions. The experimental results, including the moments of inertia and angular momentum alignments of nine bands in ^178W, are reproduced well by the particle-number conserving calculations, in which no free parameter is involved. Calculations demonstrate that occurrence of sharp backbending comes mainly from the contribution of high-j intruder orbitals vi13/2 or πh11/2 and their interference effect with orbitals near the Fermi surface. Theω variation of the occupation probability of each cranked orbital and the contribution to moment of inertia from each cranked orbital are analyzed.     

Proton Orbital [541]1/2 and Backbending in 178W

The microscopic mechanism of nine experimentally observed bands in ¹⁷⁸W is investigated using the particle-number conserving method of the cranked shell model with monopole and quadrupole paring interactions. The experimental results, including the moments of inertia and angular momentum alignments of nine bands in ¹⁷⁸W, are reproduced well by the particle-number conserving calculations, in which no free parameter is involved. Calculations demonstrate that occurrence of sharp backbending comes mainly from the contribution of high-j intruder orbitals νi13/2 or πh11/2 and their interference effect with orbitals near the Fermi surface. The ω variation of the occupation probability of each cranked orbital and the contribution to moment of inertia from each cranked orbital are analyzed.     

In-band M1 and E2 transition rates and collective structures in Ba

Subpicosecond mean lifetimes of eight excited states in ¹²⁸Ba populated via the ⁹⁶Zr(³⁶S,4n) reaction were measured by the Doppler-shift attenuation (DSA) technique using a line-shape analysis. The differential decay-curve method (DDCM) was applied for the lifetime determination. The B(E2) values in the yrast band indicate that the first band-crossing is with a proton S-band. The configuration πh_11/2d_5/2 of the negative-parity semi-decoupled bands is confirmed by the measured B(E2, I → I − 2) and B(M1, I → I − 1) transition strengths. The higher-lying “dipole” band in ¹²⁸Ba can be described as a high-K four-quasiparticle band built on the prolate configuration (πh_11/2d_5/2) (νh_11/2g_7/2).     

Backbending in theN=96 isotones

The backbending in the even-even,N=96 isotones can be quantitatively accounted for by the rotation-alignment of the spins of neutrons in i 13/2 orbits, as shown by comparing the aligned angular momentum and relative Routhian for thes-bands in these isotones and for the i 13/2 bands in the corresponding isotopes withN=91. The influence of protons on this backbending situation is shown to be indirect, acting through a change of the nuclear deformation, which yields a change of the moment of inertia of the g.s. band and of the non-rigid character of the rotation. The experimental data on theN=96 and 97 isotones are in reasonable agreement with cranking model calculations. Possible reasons for the inhibition of backbending in the h 9/2 proton bands in the odd-Z, N=96 isotones, all related to a change of deformation, are presented.     

“Backbending” in the Stephens-Simon model

In an attempt to understand the backbending phenomena observed in the rare-earth region a model representing an extension of the rotational alignment scheme has been investigated. It is found, even including attenuation of the Coriolis matrix elements and taking into account the sensitivity of the results on the single-particle spectrum used, that it appears at the moment impossible to decide whether such a model ultimately may lead to an explanation of the observed changes in the nuclear moment of inertia.     

Electron impact ionization of Ba,Ba+ and Ba2+

The binary encounter approximation has been used to investigate the effect of charge state of the target atom (ion) on the electron impact excitation autoionization cross-sections. Roothan-Hartree-Fock (RHF) velocity distribution for the bound electrons has been used through-out the calculations. The present results give a good account of the experimental observations.     

Isotopieverschiebung der Bariumnuklide140Ba,138Ba,136Ba und134Ba in der Ba II-Resonanzlinie 6p 2 P 1/2-6s 2 S 1/2

In principle, the surface resistance of superconductors forRF can be calculated in the framework of the BCS-theory. However, even in the simplest case (low rf field strengths and Meissner phase), the theory yields complicated expressions, which need a computer for solving; the results are shown as graphs. To avoid the use of these complicated expressions, we discuss these numerical results in a model which allows an understanding of the unusual dependencies on the material parameters of superconductors. The theoretical results are compared with new experiments on Nb and on alloys showing, that the surface resistance of superconductors give additional information on the superconducting material in the penetration region.     

An IBM2 Description of the E(5) Symmetry in 134Ba and 108pd

With the low-lying energy levels, E2 transition branching ratios and absolute transition rates of the 134Ba and 108Pd, are investigated in the neutron-proton interacting boson model (IBM2) which includes the quadrupole quadrupole interaction between like bosons and the E(5) symmetry, it shows that the IBM2 can describe the nuclei at critical point of a phase transition well.     

An IBM2 Description of the E(5) Symmetry in 134Ba and 108Pd

With the low-lying energy levels, E2 transition branching ratios and absolute transition rates of the ¹³⁴Ba and ¹⁰⁸Pd, are investigated in the neutron-proton interacting boson model (IBM2) which includes the quadrupole-quadrupole interaction between like bosons and the E(5) symmetry, it shows that the IBM2 can describe the nuclei at critical point of a phase transition well.     

Backbending behaviour of rotational bands in 163,165,167Yb

Several rotational bands in ^163,165,167Yb are observed in (HI,xnγe^?) experiments. The $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ and $\text{3}\text{2}{}^{\mathrm{?}}\text{[521]}$ bands do not backbend, whereas the $\text{5}\text{2}{}^{\mathrm{?}}\text{[523]}$ bands do, indicating additional processes besides the rotational alignment of one $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ neutron pair that are responsible for the backbending.     

Ba nuclear resonance in YBa2Cu2Oy

The first observations of NMR and NQR of both isotopes¹³⁵Ba and¹³⁴Ba in isotopically enriched samples of YBa₂Cu₃O_y with oxygen concentrations y=6.0, 6.2, and 7.0 are described. The pure NQR frequencies and asymmetry parameter are in good agreement with theoretical predictions. The temperature dependence of the NQR frequency of Ba for y=7 is qualitatively similar to that for Cu(2) but much stronger. The temperature dependence of the longitudinal and transverse relaxation times opens new questions.     

Evidence for a possible E(5) symmetry in 134Ba

Evidence for the first empirical example of a transitional dynamical symmetry at a critical point is discussed in the spectrum of 134Ba. The role of such classes of symmetries in nuclear structural evolution is also discussed.     

Low-temperature phase transition in Ba2TiGe2O8

Previous work on Ba₂TiGe₂O₈ crystals has shown an unusual low-temperature (～ 223 K on cooling, ～ 273 K on heating) phase transition. Precession x-ray photographs on Ba₂TiGe₂O₈ single crystals show an incommensurate modulation along b*, and, for the first time, also along a*. Single crystal intensity data confirm the average structure in space group Cmm2. There is positional disorder in the pyrogermanate groups, and this is the probable cause for the modulated structure. The low-temperature phase transition is proposed to be a lock-in transition, with the modulation along a* locking in at a value of 1/3. Several properties, as well as other unusual features of the low-temperature phase transition, are discussed in light of the proposed lock-in transition. Domain studies show that the ferroelastic domains are unstable in the low-temperature phase.     

Synthesis and Luminescence of Ba2ScCl7

Physics of the Solid State - New results on luminescence in Ba2ScCl7 are reported. Lanthanides Eu2+ and Ce3+ were chosen as activators. The phosphors could be prepared by a simple wet chemical...     

原子核代数模型中的F-旋混合态、回弯、电磁跃迁问题的研究

在原子核的代数模型框架下,讨论了集体回弯效应、较高自旋的Ｆ－旋混合对称态以及电磁跃迁几率等问题． The collective backbending effect, F spin mixed symmetry states have been studied for the nuclei with moderate high spins. It is found that there is an additional L(L+3) proportional term in the E2 transition rates in the sdg interacting boson model and solved the long standing problem of reduction of collectivity in the wave function of boson models. The electromagnetic transitions in the spdf interacting boson model have been calculated and compared with existing experimental...     

Backbending in 167Hf and 168Hf and the band-crossing picture

Using two Compton-suppression spectrometers in an E_γ?E_γ coincidence experiment, the yrast bands in ^167,168Hf were extended up to $\text{49}\text{2}$ and 28 ?, respectively. The i ${}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ positive parity band in ¹⁶⁷Hf experiences backbending at a higher frequency than the first backbending in ¹⁶⁸Hf, and no second backbending is obseerved in ¹⁶⁸Hf. New information is threby obtained on the nature and interaction strength of the crossing bands in the vicinity of N = 96.