Excited rotational bands in the high-spin region of deformed nuclei

Rotational bands of deformed nuclei in the rare-earth region in the vicinity of the yrast line are investigated within the framework of the random phase approximation based on a self-consistent solution of the Hartree-Fock-Bogolyubov equations in the rotating system. For low angular momenta one finds the well-known β, δ and γ vibrational bands and non-collective two-quasiparticle bands. In the high-spin region additional aligned bands develop. They are dramatically lowered in energy by the Coriolis interaction. Several band crossings occur. The calculated spectra are in fair agreement with experimental measurements.     

On the properties of the extended ground rotational bands in actinide even-even nuclei

The energies of the yrast levels extending up to I = 28 in even-even actinide nuclei were analyzed in terms of an angular velocity expansion E_rot(I) = ∑_i=1ⁿα_iω_I²ⁱ with n = 2?7 to test the application of this expansion to high spin. A strong ω²-dependence is observed for the Variable Moment of Inertia model (VMI) with two parameters α_i(ω²), particularly at the higher spins. There is a marked difference in the ω²-dependence, of these parameters between the N = 142 and other nuclei studied in this region to indicate structure effects are present at the higher spin.     

IBA,macroscopic SU(3) and microscopic description of ground state bands in rotational nuclei

The number of bosons deduced from variational calculations of spectra and intrinsic mass quadrupole moments of heavy deformed nuclei are compared with predictions of IBA in the SU(3) limit. The differenct between the two suggest the need for including l > 2 bosons in IBA.     

The ground state of deformed nuclei as a boson condensate

It is shown that the ground state of deformed nuclei can be considered as a condensate of bosons that do not have a well-defined angular momentum. Values for the quadrupole moment and the particle number that are very close to the values obtained using the full boson wave function are obtained by retaining only the s- and d-parts of the boson wave function.By comparing with the many-shell (realistic) situation we found the limitations of the single-shell calculations.     

Scars of discrete rotational bands in hot nuclei

Rotational motion loses its coherence as a function of the nuclear internal excitation energy. The damping process does not proceed in a continuous fashion and scars of discrete rotational bands are found, inbedded in a background of damped rotational states, regardless whether the calculations are carried out using effective or “random” forces. The complexity of the damping mechanism is revealed in the lineshape of the ridges in theγ-γ correlation spectrum.     

Scars of discrete rotational bands in hot nuclei

Rotational motion loses its coherence as a function of the nuclear internal excitation energy. The damping process does not proceed in a continuous fashion and scars of discrete rotational bands are found, inbedded in a background of damped rotational states, regardless whether the calculations are carried out using effective or “random” forces. The complexity of the damping mechanism is revealed in the lineshape of the ridges in the γ-γ correlation spectrum.     

On the interpretation of rotational bands in odd actinide nuclei

While the cranked quasiparticle model gives too large alignment of angular momentum for the ground state bands of ²³⁵U and ²³⁷Np, the empirical alignments are well reproduced in a quasiparticle plus rotor model with a rotation dependent interaction between core and quasiparticle. This model also gives better agreement with the data than a cranked quasiparticle model with Coriolis attenuation.     

On the fine structure of the rotational bands of superdeformed nuclei

It is shown that the staggering of the energy levels of the superdeformed rotational bands can be explained from first principles, using the standard microscopic Hamiltonian with the pairing, quadrupole, and hexadecapole residual interactions, as resulting from rotation-induced nonadiabatic distortion of the mean field in the nucleus. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 231–236 (25 August 1996)     

On the description of collective negative parity bands in even-even deformed nuclei

The collective bands of negative parity are studied via a microscopic approach where Coriolis forces and octupole correlations are treated on an equal footing. The apparent moment of inertia of these bands are nicely reproduced.     

Comparison between formulas of rotational band for axially symmetric deformed nuclei

The experimental rotational spectra of the deformed nuclei available in even-even and odd-A nuclei in the rare-earth and actinide regions are systematically analyzed with several rotational spectra formulas,including Bohr-Mottelson's I(I+l)-expansion,Harris'w2-expansion,ab and abc formulas.It is shown that the simple 2-parameter ab formula is much better than the widely used 2-parameter Bohr-Mottelson's AB formula and Harris'αβ formula.The available data of the rotational spectra of both ground-state band in even-even nuclei and one-quaasiparticle band in odd-A nuclei can be conveniently and rather accurately reproduced by ab formula and abc formula.The moment of inertia and the variation with rotational frequency of angular momentum can be satisfactorily reproduced by ab and abc formulas.     

Comparison between formulas of rotational band for axially symmetric deformed nuclei

The experimental rotational spectra of the deformed nuclei available in even-even and odd-A nuclei in the rare-earth and actinide regions are systematically analyzed with several rotational spectra formulas, including Bohr-Mottelson's I(I+1)-expansion, Harris' ω²-expansion, ab and abc formulas. It is shown that the simple 2-parameter ab formula is much better than the widely used 2-parameter Bohr-Mottelson's AB formula and Harris'αβ formula. The available data of the rotational spectra of both ground-state band in even-even nuclei and one-quasiparticle band in odd-A nuclei can be conveniently and rather accurately reproduced by ab formula and abc formula. The moment of inertia and the variation with rotational frequency of angular momentum can be satisfactorily reproduced by ab and abc formulas.     

The ground state rotational constants of NNO

We report new measurements of the 5 ← 4 through 9 ← 8 lines in the pure rotational spectrum of nitrous oxide, ¹⁵N¹⁵N¹⁶O, and measurements at room temperature and at an elevated temperature of the 10⁰0-00⁰0 and 02⁰-00⁰0 bands of that molecule. The new data together with data for 10 other vibration-rotational transitions which previously have been reported enable us to determine the ground state constants. Using the newly determined values of B₀₀₀, D₀₀₀, and H₀₀₀, we have determined the band origins and the upper state constant differences B - B₀₀₀, D - D₀₀₀, and H - H₀₀₀ of 25 vibration-rotational bands whose lower level is the ground vibrational state.     

The rotational spectrum of the ground state of methylamine

Recent progress is reported in measuring, assigning, and fitting the rotational spectrum of the ground vibrational state of methylamine, CH₃NH₂, a spectrum complicated both by internal rotation of the methyl top and by inversion of the amino group. New measurements of 513 rotational transitions with J up to 30 and K up to 9 were carried out between 49 and 326 GHz using the millimeter-wave spectrometer in Kharkov. After removing the observed quadrupole hyperfine splittings, these new data along with previously published measurements were fitted to a group-theoretical high-barrier tunneling Hamiltonian from the literature, using 53 parameters to give an overall weighted standard deviation of 0.80 for 850 far-infrared and 673 microwave transitions in the ground state. The root-mean-square deviation of 0.018 MHz obtained for 346 millimeter-wave transitions measured with 0.020 MHz uncertainty represents an approximately 30-fold improvement in fitting accuracy over past attempts.     

The study of the ground state rotational bands in U 233 and U 235 by the inelastic scattering of deuterons

The ground state rotational bands in the odd isotopes of uranium U 233 and U 235, were studied by the inelastic scattering of 13.1 MeV deuterons. Seven members of these bands were seen in both nuclei. By fitting the experimental energies of the levels to the relation E(I)= =AI(I+1)+B[I(I+1)]², the parametersA andB were determined. Their values and the upper limits of the quadrupole reduced transition probabilities determined from the cross sections were: U 233:A=(5.93±0.10)keV,B=(?0.002±0.001)keV,B(E2,5/2→7/2)= =(6.51±0.66)×10^?48 e² cm⁴,B(E2,5/2→9/2)=(2.80±0.37) X 10^?48 e² cm⁴. U 235:A=(5.36±0.04)keV,B=(?0.0017±0.0004) keV,B(E2,7/2→9/2)=(8.05±0.71) × × 10^?48 e² cm⁴,B(E2,7/2→11/2)=(2.17±0.39) X 10^?48 e² cm⁴.     

Coriolis coupling and electromagnetic properties of rotational bands in odd-a Yb nuclei

Properties of the rotational bands in¹⁶⁷Yb are studied using the quasiparticle-phonon model with the Coriolis interaction included. The level energies,B(E2) andB(M1) values, E2/M1 mixing ratios, and magnetic moments are calculated. In particular, theB(E2) values and the E2/M1 mixing ratios measured by using delay coincidence and nuclear orientation methods, respectively, are well reproduced.Dedicated to Professor Ivan Úlehla on the occasion of his sixtieth birthday.