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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Rotational excitations in rare-earth nuclei: A comparative study within three cranking models with different mean fields and treatments of pairing correlations

High-spin rotational bands in rare-earth Er (Z = 68), Tm (Z = 69), and Yb (Z = 70) isotopes are investigated by three different nuclear models. These are (i) the cranked relativistic Hartree-Bogoliubov (CRHB) approach with approximate particle number projection by means of the Lipkin-Nogami (LN) method, (ii) the cranking covariant density functional theory (CDFT) with pairing correlations treated by a shell-model-like approach (SLAP) or the so-called particle-number conserving (PNC) method, and (iii) cranked shell model (CSM) based on the Nilsson potential with pairing correlations treated by the PNC method. A detailed comparison between these three models in the description of the ground-state rotational bands of even-even Er and Yb isotopes is performed. The similarities and differences between these models in the description of the moments of inertia, the features of band crossings, and equilibrium deformations and pairing energies of the even-even nuclei under study are discussed. These quantities are considered as a function of rotational frequency and proton and neutron numbers. The changes in the properties of the first band crossings with increasing neutron number in this mass region are investigated. On average, a comparable accuracy of the description of available experimental data is achieved in these models. However, the differences between model predictions become larger above the first band crossings. Because of the time-consuming nature of numerical calculations in the CDFT-based models, a systematic study of the rotational properties of both ground-state and excited-state bands in odd-mass Tm nuclei is carried out only by the PNC-SCM. With few exceptions, the rotational properties of experimental 1-quasiparticle and 3-quasiparticle bands in 165,167,169,171 Tm are reproduced reasonably well. As a result, the appearance of backbendings or upbendings in these nuclei is well understood from the analysis of the variations of the occupation probabilities of the single-particle states and their contributions to total angular momentum alignment with rotational frequency.

150 ≤ A ≤ 189↗
DOE OSTI2010

The Study of High Spin States in Nuclear Rotation by the Cranked Nilsson Strutinsky Model

A heavy-ion reaction can populate nuclear states of very high angular momentum with values of the order of I = 60 achievable. The reaction produces such configurations with a considerable internal excitation, but the emission of a few neutrons reduces the excitation energy effectively while not decreasing the spin by much. At sufficiently high spin the pairing is destroyed completely and the rigid-body moment of inertia becomes a good approximation. Even in this regime, however, the single-particle structure remains important and shell effects can be studied in terms of a rotating phenomenological shell model. On the theoretical side the cranked Nilsson strutinsky model has proved to be a successful tool to describe rapidly rotating nucleus. Indeed, this model gives a microscopic description of the influence of rotation on single-particle motion. This paper will concentrate on introduction to the cranked Nilsson strutinsky model in details. First, we explain the cranking model and the rotating liquid-drop model, then introduce the shell correction method. Also, we describe terminating bands, which show a continuous transition from high collectivity to a pure particle-hole state.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

New high-spin level schemes and excitation modes of 117,118,119,120,122 Cd

High-spin level schemes of {sup 117,118,119,120,122}Cd are expanded by analyzing our high-statistics triple and higher-fold coincidence events of prompt fission {gamma} rays from {sup 252}Cf at Gammasphere. Spin/parity assignments were made based on new {gamma}-{gamma} angular correlation measurements and level systematics in the neighboring isotopes. Stretch-aligned band structures observed in low-lying levels in {sup 117,119,121}Cd are seen to weaken with increasing spins, with a quasi-rotational degree of freedom manifested at higher spins. The{sup 5-}levels in even-N{sup 118,120}Cd were tentatively interpreted as candidates of quadrupole-octupole (QOC) coupling. The model-independent spin versus {h_bar}{omega} curves for even-N and odd-N Cd isotopes imply quasirotational alignment of an h11/2 neutron pair in the even-N Cd isotopes. The relative energies of the lowest 11/{sup 2-}, 9/{sup 2-}, 7/{sup 2-}, and 15/{sup 2-} levels in {sup 117}Cd and {sup 119}Cd suggest triaxial shapes based on Meyer-Ter-Vehn theory for these odd-N Cd nuclei. For the even-N Cd isotopes evidence of triaxiality may also be provided by the Shell Correction version of the Tilted Axis Cranking model (SCTAC).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Relation between the mass coefficients for rotational and {gamma}-vibrational modes in well-deformed nuclei

The ratio of the mass coefficients for the {gamma}-vibrational and rotational motion for the well-deformed axially symmetric nuclei is calculated basing on the Cranking model and the Random Phase Approximation. The results obtained show that the calculated ratio is equal to 2-3, i.e., significantly larger than unit. This is in a qualitative agreement with the experimental data.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Semiclassical approaches to nuclear dynamics

The extended Gutzwiller trajectory approach is presented for the semiclassical description of nuclear collective dynamics, in line with the main topics of the fruitful activity of V.G. Solovjov. Within the Fermi-liquid droplet model, the leptodermous effective surface approximation was applied to calculations of energies, sum rules, and transition densities for the neutron–proton asymmetry of the isovector giant-dipole resonance and found to be in good agreement with the experimental data. By using the Strutinsky shell correction method, the semiclassical collective transport coefficients, such as nuclear inertia, friction, stiffness, and moments of inertia, can be derived beyond the quantum perturbation approximation of the response function theory and the cranking model. The averaged particle-number dependences of the low-lying collective vibrational states are described in good agreement with the basic experimental data, mainly due to the enhancement of the collective inertia as compared to its irrotational flow value. Shell components of the moment of inertia are derived in terms of the periodic-orbit free-energy shell corrections. A good agreement between the semiclassical extended Thomas–Fermi moments of inertia with shell corrections and the quantum results is obtained for different nuclear deformations and particle numbers. Shell effects are shown to be exponentially dampted out with increasing temperature in all the transport coefficients.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

On the moment of inertia of a quantum harmonic oscillator

An original method for calculating the moment of inertia of the collective rotation of a nucleus on the basis of the cranking model with the harmonic-oscillator Hamiltonian at arbitrary frequencies of rotation and finite temperature is proposed. In the adiabatic limit, an oscillating chemical-potential dependence of the moment of inertia is obtained by means of analytic calculations. The oscillations of the moment of inertia become more pronounced as deformations approach the spherical limit and decrease exponentially with increasing temperature.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Semiclassical shell-structure moment of inertia for equilibrium rotation of a simple Fermi system

Semiclassical shell-structure components of the collectivemoment of inertia are derived within the mean-field cranking model in the adiabatic approximation in terms of the free-energy shell corrections through those of a rigid body for the statistically equilibriumrotation of a Fermi system at finite temperature by using the nonperturbative extended Gutzwiller periodic-orbit theory. Their analytical structure in terms of the equatorial and 3-dimensional periodic orbits for the axially symmetric harmonic oscillator potential is in perfect agreement with the quantum results for different critical bifurcation deformations and different temperatures.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Semiclassical shell structure in rotating Fermi systems

The collective moment of inertia is derived analytically within the cranking model for any rotational frequency of the harmonic-oscillator potential well and at a finite temperature. Semiclassical shell-structure components of the collective moment of inertia are obtained for any potential by using the periodic-orbit theory. We found semiclassically their relation to the free-energy shell corrections through the shell-structure components of the rigid-body moment of inertia of the statistically equilibrium rotation in terms of short periodic orbits. The shell effects in the moment of inertia exponentially disappear with increasing temperature. For the case of the harmonic-oscillator potential, one observes a perfect agreement of the semiclassical and quantum shell-structure components of the free energy and the moment of inertia for several critical bifurcation deformations and several temperatures.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Octupole correlations near Te 110

The lifetime of the 2 + and 9 – , 11 – , 13 – , 15 – states in the neutron-deficient 110 Te was measured for the first time using the recoil distance Doppler shift technique. The reported value of the reduced transition probability B(E2; $0$$^{+}_{g.s}$ → 2 + ) = 4.3(8) × 10 3 e 2 fm 4 supports the systematic for even-mass Te isotopes and was interpreted in the framework of the large-scale shell model and cranked shell model calculations. The measured reduced transition probabilities in the negative-parity yrast band revealed the upward trend towards the high spins. Furthermore, the enhanced collectivity is discussed in terms of the tilted axis cranking approach and the symmetry configuration mixing method with the Gogny D1S interaction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Two-phonon {gamma}-vibrational states in rotating triaxial odd-A nuclei

The distribution of the two-phonon {gamma}-vibrational collectivity in the rotating triaxial odd-A nucleus {sup 103}Nb, which is one of the three nuclides for which experimental data were reported recently, is calculated in the framework of the particle vibration coupling model based on the cranked shell model plus random phase approximation. This framework was previously utilized for analyses of the zero- and one-phonon bands in another mass region and is applied to the two-phonon band for the first time. In the present calculation, three sequences of two-phonon bands share collectivity almost equally at finite rotation whereas the K={Omega}+4 state is the purest at zero rotation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Shape evolutions in the neutron-rich Ru isotopes

Shape evolutions in the neutron-rich Ru isotopes were investigated using the cranked shell model and an excellent agreement was obtained in comparison with the experimental data. These results show that the cranked shell model with nonaxial deformed Woods-Saxon potential can provide a good description of the shape evolution in the neutron-rich Ru isotopes in terms of not only neutron number but also angular momentum.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Rotational band structure in Mg 32

There is significant evidence supporting the existence of deformed ground states within the neutron-rich N ≈ 20 neon, sodium, and magnesium isotopes that make up what is commonly called the “island of inversion.” However, the rotational band structures, which are a characteristic fingerprint of a rigid nonspherical shape, have yet to be observed. Here, in this work, we report on a measurement and analysis of the yrast (lowest lying) rotational band in 32 Mg up to spin I = 6 + produced in a two-step projectile fragmentation reaction and observed using the state-of-the-art γ-ray tracking detector array, GRETINA (γ-ray energy tracking in-beam nuclear array). Large-scale shell-model calculations using the SDPF-U-MIX effective interaction show excellent agreement with the new data. Finally, a theoretical analysis of the spectrum of rotational states as a function of the pairing gap, together with cranked-shell-model calculations, provides intriguing evidence for a reduction in pairing correlations with increased angular momentum, also in line with the shell-model results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

Structure changes in {sup 160}Er from low to ultrahigh spin

A spectroscopic investigation of the {gamma} decays from excited states in {sup 160}Er has been performed in order to study the changing structural properties exhibited from low spin up toward ultrahigh spin (I{approx}60({h_bar}/2{pi})). The nucleus {sup 160}Er was populated by the reaction {sup 116}Cd({sup 48}Ca,4n{gamma}) at a beam energy of 215 MeV, and resulting {gamma} decays were studied using the Gammasphere spectrometer. New rotational structures and extensions to existing bands were observed, revealing a diverse range of quasiparticle configurations, which are discussed in terms of the cranked shell model. At spins around 50({h_bar}/2{pi}) there is evidence for oblate states close to the yrast line. Three rotational bands that have the characteristics of strongly deformed triaxial structures are observed, marking a return to collectivity at even higher spin. The high-spin data are interpreted within the framework of cranked Nilsson-Strutinsky calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

Multi-quasiparticle structures up to spin {approx}44({h_bar}/2{pi}) in the odd-odd nucleus {sup 168}Ta

High-spin states in the odd-odd nucleus {sup 168}Ta have been populated in the {sup 120}Sn({sup 51}V,3n) reaction. Two multi-quasiparticle structures have been extended significantly from spin {approx}20({h_bar}/2{pi}) to above 40({h_bar}/2{pi}). As a result, the first rotational alignment has been fully delineated and a second band crossing has been observed for the first time in this nucleus. Configurations for these strongly coupled rotational bands are proposed based on signature splitting, B(M1)/B(E2) ratio information, and observed rotation-alignment behavior. Properties of the observed bands in {sup 168}Ta are compared to related structures in the neighboring odd-Z, odd-N, and odd-odd nuclei and are discussed within the framework of the cranked shell model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

High-spin spectroscopy in {sup 125}Xe

Levels excited up to 39.8 MeV and 119/2 units of angular momentum have been populated in {sup 125}Xe by the {sup 82}Se({sup 48}Ca,5n){sup 125}Xe reaction. High-fold {gamma}-ray coincidence events were measured using the Gammasphere Ge detector array. Nine regular rotational bands extending from levels identified previously up to almost 60 ({h_bar}/2{pi}) have been identified, and three of these have been connected to low-lying levels having well-established spins and parities. Configurations have been assigned to six of the bands based on alignment properties, band crossings, and comparison with theoretical cranked shell model calculations (CSM). Transition quadrupole moments have been measured for these bands in the spin range 31-55 ({h_bar}/2{pi}) and were found to be in agreement with the CSM calculations. The corresponding quadrupole deformation {epsilon}{sub 2} ranges from 0.28 to 0.34 at a {gamma} deformation of 0 deg. and from 0.29 to 0.36 at a {gamma} value of 5 deg.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2011

The influence of quasineutron configurations on {sup 161}Ta and nearby odd-A nuclei

Several strongly coupled bands in the neutron-deficient nucleus {sup 161}Ta have been identified and quasiparticle configuration assignments have been made on the basis of rotational alignments and cranked shell model calculations. The level scheme elucidated for {sup 161}Ta highlights the competition between the {nu}(h{sub 9/2}) and {nu}(i{sub 13/2}) orbitals to form the yrast spectrum. The band structures in {sup 161}Ta also provide new insights into the structural features of other heavy odd-A nuclei populated with much lower reaction cross sections in this region at the proton drip line.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Discovery of the new isotope 251 Lr and the α-decay fine structure in 253 L

The products of the 203, 205 Tl ( 50 Ti, 2n) fusion-evaporation reactions were studied using the recently commissioned Argonne Gas-Filled Analyzer at Argonne National Laboratory. Two α-decay activities with energies of 9210(19) and 9246(19) keV and half-lives of $42^{+42}_{-14}$ and $24.4^{+7.0}_{-4.5}$ ms were observed which were followed by the known α decays of 247 Md and 243 Es . They are interpreted as originating from the 1/2 ⁻ [521] and 7/2 ⁻ [514] single-proton Nilsson states in the hitherto unknown isotope 251 Lr . From the measured Q α values the 1/2 ⁻ level was placed 117(27) keV above the 7/2 - level in 251 Lr in contrast to 255 Lr where the 1/2 ⁻ level is the lowest. Also, the α decay of 253 Lr was studied in more detail and a new α line at 8660(20) keV was found and a new half-life value of 2.46(32) s for an isomeric state in 253 Lr was measured. The 251, 253, 255 Lr Q α values were compared with predictions of various mass models. The relative energies of the 1/2 ⁻ [521] and 7/2 ⁻ [514] single-proton Nilsson states in 251, 253, 255 Lr isotopes were compared with results of the cranking shell model with pairing treated using the particle-number-conserving method. The level separation and, in particular, the level order change between 251 Lr and 255 Lr was reproduced only when the hexacontetrapole deformation ϵ 6 was included in the calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗