Shell effects on rotational damping in superdeformed nuclei

Damping of collective rotational motion in A ∼ 190 and A ∼ 150 superdeformed nuclei is studied by means of the cranked shell model with two-body residual force. Numerical calculations predict that in a typical A ∼ 190 superdeformed nucleus, ¹⁹²Hg, the rotational damping width is significantly small, Γ_rot ∼ 30 keV, and that the number of superdeformed bands in the offyrast region amounts up to 150 at a given rotational frequency. These features are quite different from the prediction for A ∼ 150 superdeformed nuclei and rare-earth normally deformed nuclei. It is shown that the single-particle alignments of the cranked Nilsson orbits have strong shell oscillation. It affects significantly the properties of rotational damping in superdeformed ¹⁹²Hg.     

Spectroscopy of195Hg and196Hg

High-spin states in the oblate-deformed nuclei¹⁹⁵Hg and¹⁹⁶Hg were populated in the¹⁹⁸Pt(α, xn) reaction and investigated by in-beamγ-ray spectroscopy using six Compton-suppressed Ge detectors. The level schemes of both nuclei are extended considerably. The level structure is interpreted within the framework of the cranked shell model. Good agreement is obtained between model predictions and experimental results.     

High-spin structure of 190–194Hg and the cranked shell model

High-spin states in ^190–194Hg, populated in the ¹⁷⁰Er (^{24, 26}Mg, xn) and ^{184, 186}W(¹³C, xn) reactions, were investigated by in-beam γ-ray spectroscopic techniques. The level schemes in all five nuclei were extended to considerably higher spins and new band intersections were found. The band structure is interpreted within the framework of the cranked shell model. Remarkable agreement is obtained between the predictions of the model and the experimental data for these weakly oblate deformed nuclei. In ^{192, 194}Hg irregular sequences were found which could be examples of “ terminating bands”.     

Structure of neutron-rich s-d shell nuclei

States in neutron-rich s-d shell nuclei were populated in the reaction of a ¹⁴C beam at E _lab=22 MeV on a ¹⁴C target. Coincidences between γ rays and either other γ rays or light charged particles were measured. γ rays in coincidence with protons established levels at 66.8, 1730, 1823, and 2219 keV in ²⁷Na. The states are compared with calculations based on the s-d shell model and the cranked Nilsson-Strutinsky model. A number of levels in ²⁴Ne were observed in both α-γ and α-γ-γ coincidences and are compared with shell-model calculations.     

Properties of side bands observed in180Os

Bands in ¹⁸⁰ Os have been studied with in-beam spectroscopy methods. Four side bands were established. Configurations have been assigned to them considering the features of similar bands in neighbouring nuclei. New aspects result from an interpretation in the framework of the cranked shell model.     

On the moment of inertia in deformed Ba-Xe nuclei as deduced from gamma-gamma energy correlation experiments

The γ-rays following reactions induced by bombarding targets of ^{114, 116, 118, 120, 122}Sn with 118 MeV ¹²C ions were investigated using six NaI(Tl) detectors in a two-dimensional coincidence arrangement. Experimental energy-correlation spectra were extracted from the original coincidence matrices. The energy-correlation spectra exhibit the features expected for rotational nuclei and were used to deduce information on the moment of inertia $\text{I}{}^{\mathrm{(2)}}\text{= ΔI/Δω}$. The gross properties of the behaviour of $\text{I}$⁽²⁾ in the Ba-Xe region are discussed together with their interpretation within the cranked shell model (CSM).     

Pionic degrees of freedom in atomic nuclei and quasielastic knockout of pions by high-energy electrons

The microscopic mechanism of the identical bands in odd-odd nucleus ¹⁹⁴Tl and its neighbor odd-A nuclei ^193,195Tl is investigated using the particle-number-conserving (PNC) method for treating the cranked shell model with monopole and quadrupole pairing interactions. It is found that the blocking effect of the high-j intruder orbital plays an important role in the variation of moments of inertia (J⁽¹⁾ and J⁽²⁾) with rotational frequency for the superdeformed bands and identical bands. The variation of the occupation probability of each cranked orbital and the contributions to moment of inertia from each cranked orbital are presented.     

Symmetry-conserving Hartree-Fock-Bogoliubov theory: (II). Number-projected cranked Hartree-Fock-Bogoliubov calculations in the rare earth region

The yrast line of the nuclei ¹⁶⁴Er and ¹⁶⁸Er is investigated within the cranking approximation by a full variation after exact number projection. The results are compared with those of the cranked shell model and of a self-consistent solution without number projection. In particular we discuss the behavior of pairing correlations in the region of very high spins, where a phase transition is expected.     

The statistical properties of single-particle levels in rotating heavy nuclei

The single particle-energy levels of U ₉₂ ²³⁸ as a function of cranked frequency are given in rotating two-centre shell model. It is found that the curvature distribution approaches the prediction of Gaussian unitary ensemble (GUE) [14] for a certain range of separations between two centers at some cranked frequencies, which is the first support to the prediction in the realistic and complex system like heavy nuclei. Meanwhile, we find that the spacing distributions for various separations have a similar structure when the frequency is high, for which a formulae is suggested to describe this kind of spacing distributions. In addition, we compute the spectral rigidity characterizing the long range correlation of a spectrum.     

Inclusion of pairing into strutinsky-type cranking calculations

The shell correction method for rotating nuclei was generalized to include pairing correlations. This extends the applicability of the cranked Strutinsky-type calculations to the low-spin region. As an illustrative example the yrast-line of²⁴Mg is studied.     

High-j proton alignments in 101Pd

High-spin states in ¹⁰¹Pd have been investigated by means of in-beam γ-ray spectroscopic techniques via the ⁷⁶Ge(²⁸Si, 3n) reaction at beam energies of 85 and 95 MeV. The previously known d _5/2 and 1/2^?[550] bands were extended to higher spins, and the unfavored signature branch of the 1/2^?[550] band was built. The band crossings observed experimentally are explained by the alignment of g _9/2 protons. The band properties in ¹⁰¹Pd are compared with those in the neighboring nuclei and are discussed within the framework of the cranked shell model (CSM).     

Calculations of the energy spectra of Zn,Ga, and Ge isotopes by the shell model

The effective Hamiltonian which was determined empirically by Koops and Glaudemans is tested in shell model calculations for the^65–68Zn,^67–69Ga, and^68–70Ge nuclei in the full (1p _3/2,0f _5/2,1p _1/2) ⁿ space. The resulting energy spectra are compared with the experimental spectra and results of previous calculations. The overall agreement with experiment is as satisfactory for these nuclei as for the Ni and Cu isotopes, by which the Hamiltonian was determined. It is noticed that the spectra of⁶⁷Zn and^67,69Ga calculated in this work are similar to those provided by the Alaga model.     

Level densities of heaviest nuclei

The intrinsic level densities of superheavy nuclei in the α-decay chains of ^296,298,300120 are calculated using the single-particle spectra obtained with the modified two-center shell model. The role of the shell and pairing effects on the level density as well as their quenching with excitation energy are studied. The extracted level density parameter is expressed as a function of mass number, ground-state shell correction, and excitation energy. The results are compared with the phenomenological values of level density parameters used to calculate the survival of excited heavy nuclei.     

Rotation aligned bands and configuration dependent interaction in189Hg

High spin states in¹⁸⁹Hg have been studied using the¹⁸¹Ta(¹⁴N, 6n) reaction. The various one- and three-quasiparticle rotational bands were interpreted within the cranked shell model. The band-crossing frequencies are found to depend on the number of spectator particles. The effect can be accounted for by a residual two-body interaction of appr. ?0.11 MeV.     

Space symmetry in light nuclei. I Application to the 2s−1d shell

The Wigner supermultiplet scheme is studied in the 2s?1d shell using the spectral distribution methods of French. Expressions for the average expectation value of H and H² over states belonging to a definite SU(4) symmetry are derived. Numerical results for these averages are given for the 2s?1d shell. These averages are then used to predict ground state energies and low energy spectra for nuclei in this shell, using Ratcliff's procedure; a comparison with shell model and observed spectra is made. Mixing intensities of SU(4) representations near the ground state are also evaluated. These provide us with a measure of symmetry breaking. It appears from our calculations that the symmetry is strongly mixed. Finally a preliminary application to the theory of level densities is made.     

The low-lying rotational bands of the neutron-rich nucleus <Superscript>172</Superscript>Tm

The microscopic mechanism of four experimentally observed bands in 172Tm 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 four bands in 172Tm are reproduced well by the particle-number conserving calculations.The ω variation of the occupation probability of each cranked orbital and the contribution to moment of inertia from each c...     

Particle-Number Conserving Analysis for High K Multi-Quasiparticle Bands in Odd-A Deformed Nuclei 173,175Hf

Using the Particle-number Conserving (PNC) method for treating the cranked shell model, the high K multi-quasiparticle bands in odd-A deformed nuclei ^173,175Hf are analyzed, including the variation with rotational frequency of the moment of inertia, angular momentum alignment and occupation probability of each cranked Nilsson orbital. No free parameters are involved in the PNC calculation and the experimental results are reproduced well. The microscopic mechanism of the difference between the multi-quasiparticle high K bands and the yrast bands in neighboring even-even nuclei is investigated, where the blocking effects of high j intruder orbitals near the Fermi surface play a crucial role.     

High-spin spectroscopy of162Hf

Excited states in¹⁶²Hf were investigated up to spinI ≈ 38 using the anti-Comptonspectrometer array HERA with 21 detectors. In addition, some information was obtained on¹⁶¹Hf. The analysis of triple coincidences was crucial for the construction of the level schemes. The results are interpreted within the framework of the cranked shell model and are compared to neighbouring isotopes and isotones, showing Fermi level and deformation effects. The systematic behaviour of the band crossings in the Hf isotopes and theN=90 isotones is discussed.