Gamma Vibrational Bands and Chiral Doublet Bands in A≈100 Neutron-rich Nuclei

The level structures of neutron-rich ~(105)Mo,~(106)Mo,~(108)Mo and 110Ru nuclei in A≈100 region have been carefully investigated by coincidence measurements of the prompt γ-rays populated in the spontaneous fission of ~(252)Cf with the Gammasphere detector array.In 105Mo,one-phonon K =9/2 and two-phonon K=13/2 γ-vibrational bands have been identified.In ~(108)Mo,one-phonon γ-vibrational band is expanded and two-phonon γ-vibrational band has been identified.Two similar sets of bands in ~(106)Mo and ~(110)Ru are observed to high spins,which have been proposed as the soft chiral γ-vibrational bands.The characteristics for these γ-vibrational bands and chiral doublet bands have been discussed.     

New multi-phonon gamma vibrational bands in A∼110 neutron-rich nuclei

The high spin states of neutron-rich ¹⁰³Nb, ¹⁰⁷Tc and ¹⁰⁹Tc nuclei in A～110 region have been investigated by measuring prompt γ-γ-γ coincident measurements populated with the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. In ¹⁰³Nb, one-phonon K = 9/2 and two-phonon K = 13/2 γ-vibrational bands have been identified. In ¹⁰⁷Tc and ¹⁰⁹Tc, one-phonon K = 11/2 and two-phonon K = 15/2 γ-vibrational bands, in which the zero-phonon bands are based on K=7/2 excited states, have also been identified. The two-phonon bands are first observed in odd-Z nuclei. The characteristics for these band structures have been discussed.     

Measurements of f-numbers for α- and γ-bands of TiO

A pressure-driven shock tube has been used to measure electronic f-numbers for bands (three each) belonging to the α- and γ-band systems of titanium oxide. Observations were made at wavelengths of 6734 Å, 7147 Å, and 7689 Å in the γ-bands, and at 4969 Å, 5183 Å, and 5460 Å in the γ-bands. Observed variations in the f-numbers for a given electronic band system may perhaps be attributed to the interaction between vibrational and electronic motion.     

Collective bands in 104,106,108Mo

We have used our analysis of γ-γ-γ data (5.7 × 10¹¹ triples and higher folds) taken with Gammasphere from prompt γ rays emitted in the spontaneous fission of ²⁵²Cf to study the collective bands in ^104,106,108Mo. The one-phonon and two-phonon γ-vibrational bands and known two-quasiparticle bands in neutron-rich ^104,106Mo were extended to higher spins. The one-and two-phonon γ-vibrational bands have remarkably close energies for transitions from the same spin states and identical moments of inertia. Several new bands are observed and are proposed as quasiparticle bands in ^104,106Mo, along with the first β-type vibrational band in ¹⁰⁶Mo. The quasiparticle bands have essentially constant moments of inertia near the rigid-body value that indicate blocking of the pairing interaction. Candidates for chiral doublet bands in ¹⁰⁶Mo are strong. These are the first reported chiral vibrational bands in an even-even nucleus. The text was submitted by the authors in English.     

Levels in 156Gd studied in the (n, γ) reaction

Levels up to 2.3 MeV in ¹⁵⁶Gd have been studied using the (n, γ) reaction. Energies and intensities of low-energy γ-rays and electrons emitted after thermal neutron capture have been measured with a curved-crystal spectrometer, Ge(Li) detectors and a magnetic electron spectrometer. High-energy (primary) γ-rays and electrons have been measured with Ge(Li) detectors and a magnetic spectrometer. The high-energy γ-ray spectrum has also been measured in thermal neutron capture in 2 keV resonance neutron capture. The neutron separation energy in ¹⁵⁶Gd was measured as S_n = 8535.8 ± 0.5 keV.About 600 transitions were observed of which ~50% could be placed in a level scheme containing more than 50 levels up to 2.3 MeV excitation energy. 42 of these levels were grouped into 15 excited bands. In addition to the β-band at 1050 keV we observe 0⁺ bands at 1168, 1715 and 1851 keV. Other positive-parity bands are: 1⁺ bands at 1966, 2027 and 2187 keV; 2⁺ bands at 1154 (γ-band) and 1828 keV; and 4⁺ bands at 1511 and 1861 keV. Negative-parity bands are observed at 1243 keV (1^?), 1366 keV (0^?), 1780 keV (2^?) and 2045 keV (4^?). Reduced E2 and E0 transition probabilities have been derived for many transitions. The ground band, the β- and γ-bands and the 0⁺ band at 1168 keV have been included in a phenomenological four-band mixing calculation, which reproduces well the experimental energies and E2 transition probabilities.The lowest three negative-parity (octupole) bands of which the 0^? and the 1^? bands are very strongly mixed, were included in a Coriolis-coupling analysis, which reproduces well the observed energies. The E1 transition probabilities to the ground band are also well reproduced, while those from the higher-lying 0⁺ bands to the octupole bands are not reproduced. Absolute and relative transition probabilities have been compared with predictions of the IBA model and the pairingplus-quadrupole model. Both models reproduce well the E2 transitions from the γ-band, while strong disagreements are found for the E2 transitions from the β-band. The IBA model predicts part of the decay features of the higher lying 2⁺₂, 4⁺₁ and 2^?₁ bands.     

High-energy-resolution inelastic electron and proton scattering and the multiphonon nature of mixed-symmetry 2+ states in 94Mo

High-energy-resolution inelastic electron scattering (at the S-DALINAC) and proton scattering (at iThemba LABS) experiments permit a thorough test of the nature of proposed one- and two-phonon symmetric and mixed-symmetric 2+ states of the nucleus 94Mo. The combined analysis reveals the one-phonon content of the mixed-symmetry state and its isovector character suggested by microscopic nuclear model calculations. The purity of two-phonon 2+ states is extracted.     

Low frequency multiphonon absorption in InP:Fe

Far infrared transmission measurements have been made on iron doped crystals of InP in the 20–250 cm^?1 region at temperatures between 6 and 300 K. New weak bands were observed at 42, 83 and 113 cm^?1. The frequencies and temperature dependences of these bands indicate that they arise from two-phonon difference processes and appropriate assignments are given. Another new band observed at 65 cm^?1 is one-phonon like.     

Jahn-Teller effect in crystals: Optical response function and vibronic states

We present a method for evaluating the optical spectrum of a Jahn-Teller centre in a crystal. We are able to obtain an approximated, but not perturbative, expression for the optical response function of the system in the weak coupling case. All cases of electronic degeneracy are treated together. The general formulae giving the zero-phonon line and the one- and two-phonon bands are obtained in the two cases of Jahn-Teller interaction acting when the electron is in the ground or in an excited level. In particular, the contribution of the vibronic states as peaks in the one-phonon band is explicitly shown.     

Chemiluminescence of nitric oxide: The NO (C2Π−A2Σ+) rate constant

A rocket borne scanning $\text{1}\text{4}$-m spectrometer was used to observe the night airglow between 1900 and 2300 Å at a resolution of 15 Å. An attitude control system oriented the payload horizontally near apogee (150 km) and pointed the field of view to the north and parallel with the terminator. Progressions from the δ(0, v″) and γ(0, 0) band system of nitric oxide were observed. The observations of the δ-bands and γ-bands are consistent with the relative intensities produced in the preassociation of ground state atomic oxygen and nitrogen. An observation of the v′ = 0, ε-band progression is suggested and is consistent with the presence of a resonance fluorescence contribution near apogee. The A²Σ⁺ (upper level of the γ-bands) can only be populated by cascade from the C²π state (upper level of the γ-bands) in the preassociation reaction. In the absence of quenching of the A²Σ⁺ state, the emission rate of the γ-bands can be used as a measure of the C?A transition and thus to deduce the branching ratio to the A²Σ⁺ state. This branching ratio is estimated to be 0.21±0.04.     

(α, 2nγ) Studies of γ-vibrational and other side-bands in 162, 164, 166Er

Levels in ^{162, 164, 166}Er have been studied using the (α, 2nγ) reaction at an energy of 24 MeV. Singles spectra, γ-γ coincidence spectra, and angular distributions were obtained using Ge(Li) detectors. Transitions from levels in the γ-vibrational bands up to the 8^+' in ^{162, 164}Er and 10^+' in ¹⁶⁶Er were observed and M1/E2 mixtures were determined for many of these transitions. There is a relative shifting upward of the even-spin levels in the γ-band of ¹⁶⁶Er while the analogous levels of ^{162, 164}Er are shifted downward with the effect being most pronounced for¹⁶²Er. The standard phenomenological band-mixing parameters z₂ and z₀₂ were obtained from γ-ray branching ratio data and the values are probably correlated with the staggering of levels in the γ-bands. The ratios of the intraband and interband E2 transition strengths which are related to the intrinsic quadrupole moments of the ground-state and γ-bands are discussed. A number of other levels are observed in ¹⁶², 164Er and some of these correspond to negative parity states reported in decay studies.     

Evidence for second-phonon nuclear wobbling

The nucleus 163Lu has been populated through the reaction 139La(29Si,5n) with a beam energy of 157 MeV. Three triaxial, strongly deformed (TSD) bands have been observed with very similar rotational properties. The first excited TSD band has earlier been assigned as a one-phonon wobbling excitation built on the lowest-lying (yrast) TSD band. The large B(E2)(out)/B(E2)(in) value obtainable for one of four observed transitions between the second and first excited TSD bands is in good agreement with particle-rotor calculations for a two-phonon wobbling excitation.     

The nature of the superband in backbending for the nucleus 156Dy

In two recent publications by Broglia et al., it has been shown that backbending can be understood by mixing the ground (g) and a K = 1 (super)band (s1). It has also been claimed that a K = 0 superband (s0) is not able to reproduce the data. Here we show that, in ¹⁵⁶Dy, and with the inclusion of the γ-band, a K = 0 or a K = 1 superband can explain the data equally well. The parameters of the band-mixing model may be reduced by using, for the g-, γ- and β-bands, a generalization of the rotational-vibrational model. The g, γ, β and sK band mixing fits are greatly improved if the moment of inertia of the g-, γ- and β-bands are described by the VMI model. Inclusion of the low spin members of the superband in the fit indicates a slight preference for an sO band.     

Angular-distribution He(I) /Ne(I) /Ar(I) photoelectron spectra of unsaturated hydrocarbons

The energy dependence of the anisotropy parameters of the π- and selected σ-bands of ethylene, 1,3-butadiene, benzene, cyclohexene, norbornadiene, 1,3-and 1,4-cyclohexadiene has been determined in the low energy region. Whereas the behaviour of the σ-bands is much less uniform, all π-band β-values decrease with decreasing energy towards similar threshold values. Strong intra-band energy dependencies have been observed for both π and σ orbitals, while in the multiple π-orbital molecules there is a symmetry-specific contribution to the π β-values. Marked intensity variations are observed among the ethylene, butadiene and benzene bands, and the anisotropy-parameter-based assignment of symmetric character to the 1,4-cyclohexadiene first band is confirmed.     

Two-phonon processes in Heisenberg ferromagnet

Using the method of double-time retarded Green function, an expression for the spin energy spectrum including the contributions of one-phonon and two-phonon processes has been derived. Calculations have been performed using the spin wave approximation. The broadening of the energy level is roughly estimated in a peculiar case.I would like to thank Dr. Dagmat Fraitová for her advice and help.     

Hydrogen vibrations in γ-TiH and γ-ZrH under high pressure

Abstract

The effect of high hydrostatic pressure on the vibrational spectra of monohydrides γ-TiH and γ-ZrH was studied by inelastic neutron scattering, the maximum experimental pressure being, respectively, P=15 and 17·5 kbar. There was observed a uniform linear pressure-induced energy shift of each spectrum compared to that at ambient pressure with proportionality factors of 1·02 for y-TiH and 1·03 for γ-ZrH. The observed linear shift of the one-phonon hydrogen modes and the bound multiphonons (biphonons and triphonons) is indicative of a pressure-induced increase of the anharmonicity parameters in the model Hamiltonian representing the strength of two-phonon and three-phonon interactions.     

Elastic and inelastic scattering of 11.8 MEV polarized deuterons from 34S

The elastic and inelastic scattering of 11.8 MeV vector polarized deuterons from ³⁴S has been studied. Angular distributions of the cross section σ(θ) and vector analyzing power iT₁₁(θ) have been measured for the ground state and the first three excited states in ³⁴S. Optical model parameters were first obtained by fitting the elastic deuteron scattering data alone. DWBA calculations with a collective model form factor were performed for the inelastic scattering to the excited states. Coupled-channels calculations were also done both for the one-phonon and the two-phonon excited states. The optical model parameters were suitably modified to obtain simultaneous fit to elastic and inelastic data when channel coupling was introduced. The values of the vibrational parameter β₂ for one- and two-phonon states are discussed and compared with those obtained from γ-decay width studies.     

A study of configuration mixing in vibrational nuclei

The configuration-mixed wave functions for one-phonon and two-phonon 2⁺ states have been obtained from the experimental energy spectra of the even-even vibrational nuclei. The reduced transition probabilities and electric quadrupole moments have been calculated.     

Time-resolved hot luminescence and resonant Raman scattering: Cu2O revisited

Time-resolved resonant scattering of both one-phonon and two-phonon Raman modes at the 1s ortho-exciton state of the yellow series in Cu₂O is reported. From the time dependence of the one-phonon mode we determine the scattering rate among the triply degenerate ortho-exciton states to be 2.5 × 10⁸sec^-1. From the two-phonon modes we directly determine the exciton lifetime as a function of its kinetic energy. In both cases the resonant scattering is found to be dominated by hot luminescence.     

Critical-point analysis of the two-phonon Raman spectrum of silicon

Two-phonon Raman spectrum of silicon has been measured in back-scattering configuration at room temperature using Argon ion laser. It reveals many critical points and consists mainly of two-phonon overtone states. The agreement between the calculated density of states from neutron diffraction data and the present Raman spectrum is excellent except the region where combination spectrum appears. Polarization measurement shows that the structure centered at 300 cm^?1 is not the one-phonon fine structure, predicted by Cowley and observed in part and identified as such by Wright and Mooradian, but the two-phonon overtone spectrum of acoustic phonons. Critical-point analysis has been done on the two-phonon overtone and combination spectra, and phonon frequencies of points of high symmetry in the Brillouin zone are determined and compared with other experimental results. In contrast to the Raman spectrum of diamond, no peak was observed near twice the frequency of zone-center optical phonon. This fact is explained by the difference of phonon dispersion relation between diamond and silicon.     

The superposition of one- and two-phonon absorption and radiation in TeO2 crystal

Raman scattering and IR reflectivity for actual configuration have been investigated. The contours of reflectivity spectra rave been calculated. Phonon parameters have been determined. The temperature dependence of Raman scatterung and IR reflectivity indicated absence of soft modes in optical oscillations. Two-phonon processes of light absorption and radiation have been investigated. In the one-phonon mode frequency range, a two-phonon radiation which is completely absorbed by the crystal itself has been observed.