Rotational Damping Research Articles

Fluctuation analysis of the rotational motion of excited nuclei

The structure of excited rotational bands in well deformed nuclei is discussed. It is shown how fluctuations of 2-dimensional energy-energy γ-ray spectra can give quite detailed information about both the region of discrete bands and the region of rotational damping.

Lifetime measurements for continuum gamma rays in 164Yb and 170Hf

Lifetimes of states associated with the ridges in the E γ - E γ correlation spectrum of 164Yb and 170Hf were measured by the Doppler-shift attenuation method. The results indicate a reduction of the quadrupole collectivity associated with γ-rays with energy from 0.7 to 0.9 MeV and an enhancement of collectivity for those above 0.9 MeV. The reduced and the enhanced collectivity can be understood as rotationally-induced modifications of the occupation of high- j orbitals originating from below and above the Fermi surface, respectively. The effect of rotational damping on the lifetimes of continuum states is also discussed.

Multiple band structure and band termination in 157Ho towards complete high-spin spectroscopy

Rotational bands of 157Ho have been populated via the 124Sn(37Cl, 4n) reaction at beam energies of 155 and 165 MeV. Gamma-ray spectroscopy was performed using the 8π spectrometer at Chalk River. Many rotational bands have been observed for the first time. A detailed level scheme is presented, containing approximately 380 transitions, and the quasiparticle structure of the various bands is discussed. Band termination has been observed in the yrast states. For strongly coupled bands, B(M1)/B(E2) transition strength ratios are extracted and compared with previous measurements and theoretical expectations. Branching ratios for out-of-band E2 transitions are analysed to extract band mixing interaction strengths. Implications for rotational damping are considered. The interaction at the first backbend in the ground band is found to be strongly signature dependent; this is evidence for a signature-dependent triaxial shape of the nucleus.

Three-dimensional γ-ray correlations and the study of rotational damping in 167,168Yb

A new method of analyzing E γ1∗E γ2∗E γ3 correlation data by rotational plane mapping is discussed and applied to high spin triple data on 167,168Yb formed in 48Ca+ 124Sn reactions. Values for the rotational damping width Γ rot=124±20keV and 96 ±30 keV are found for transition energy intervals 820–980 keV and 980–1140 keV corresponding to I≈35 h ̷ and≈45 h ̷ , respectively.

NON-LINEAR DYNAMICAL INVESTIGATIONS BY USING SIMPLIFIED WHEELSET MODELS

SUMMARY A generic wheelset structure is introduced allowing investigations with conventional as well as advanced unconventional wheelsets. The axles of this generic model can include variable camber angle and coupling. The coupling can be modelled rigidly or elastically, as a passive element with rotational damping or actively with creep control. The wheel profile is simplified by a dicone whereas the rail profile is that of a UIC 60-rail. Simulations are performed for the suspended single wheelset structure as well as for a simple bogie with two wheelset structures. The results indicate the influence of the parameters velocity, cone angle and camber angle on the tangent track response of several types of passive wheelset designs. For a bogie, so far beeing equipped with two conventional wheelsets, the simulation results are compared with experiments on a 1:5-scaled roller rig.

Quantum choas and rotational damping

The appearence of quantum chaos in the excited rapidly rotating nucleus is studied in a simple nuclear model, consisting of the cranked Nilsson model with a schematic two-body interaction added. Chaos is found to smoothly set in at a much lower excitation energy in normal-deformed 168Yb than in superdeformed 152Dy. A dynamical sign of chaos is a saturation of the standard deviation of the E2-strength function, and also the disapearence of correlations in γ-γ-correlations. Motional narrowing may however restore the correlations also for the completely chaotic case. The distribution of E2-matrix elements strongly deviate from Porter-Thomas result, and many more strong γ-transitions appear than expected from GOE-theory. Transition entropy is introduced as a measure of order in the E2 cascade.

Recent studies of the high-spin quasi-continuum

Two new methods, the Rotational Plane Mapping, and the Fluctuation Analysis Method are reviewed, and applied to the study of high spin quasi-continuum states in 167,168Yb and 163Tm nuclei. New results are given for the rotational damping width Г rot and the number of different 2-step-paths below and above U 0, defined to be the energy of the borderline between undamped regular rotational motion for bands along the yrast line and the region of heated nuclei with damped rotational motion. The results indicate that at least 30 bands with regular rotational structure exist in the I = 40 region before damping becomes dominating. The fundamental concept of rotational damping may be questioned, and has never been verified experimentally. The analysis support the damping picture, giving evidence for a strong branching of the E2 decay, showing 10 times as many 2-step-paths through the continuum than expected if only regular rotational E2 decay, and E1 statistical branching were the decay modes.

A study of rotational damping in 167,168Yb

A study of rotational damping in 167,168Yb

Side-feeding times in even dysprosium isotopes

The continuum γ-decay in the isotopes 152–158Dy after heavy-ion compound reactions is studied by means of the Monte Carlo simulation. Side-feeding times, γ-ray multiplicities and intensities and E2 spectra are discussed. Rotational damping is included in the analysis. The dependence of the feeding times of yrast states on the parameters controlling the γ-decay is analyzed.

Rotational damping motion in nuclei

The recently proposed model to explain the mechanism of the rotational motion damping in nuclei is exactly solved. When compared with the earlier approximative solution, we find significative differences in the low excitation energy limit (i.e. $$\Gamma _\mu<< 2\Delta \omega _0 $$ ). For the strength functions we find distributions going from the Wigner semicircle through gaussians to Breit-Wigner shapes.

The population of the superdeformed continuum

The quasicontinuum ridge structures of superdeformed nuclei in the A=150 region are discussed in terms of a statistical model based on the Monte Carlo method, simulating the population and decay of superdeformed continuum and yrast states. A picture of the decay flow in the superdeformed quasicontinuum and its implications are presented. The role of rotational damping in the second minimum is discussed.

Fluctuation analysis of rotational motion in warm atomic nuclei

The mixing of rotational bands in warm nuclei was first considered by Georg Leander [1]. He pointed very early to posibility that the in-band decay of any given state may be spread over a broad spectrum. The B(E2) matrix elements governing rotational decay out of a mixed band state may be distributed over all final states of given parity within a certain energy interval. The width of this interval is defined as rotational damping width Frot [2]. Close to yrast line, on other hand, bands are believed to retain their structure, allowing essentially only one final state for each decay step. Figure 1 illustrates rotational decay within two regions of rotational motion, unmixed region at low excitation energy, below U0 ~ 1 MeV , and region of rotational damping at higher excitation energy above U0 (also shown schematically in insert). The intensity distributions of flow of E2 transitions along Yrast line are also indicated on this figure with dark area representing expected decreasing intensity in discrete region, for increasing spin.

Study of spin-temperature effects using energy-ordered continuum gamma-ray spectroscopy technique

We have investigated a new continuum γ -ray spectroscopy technique which is based on the detection of all emitted γ rays in a 4π detector system, and ordering them according to their energies on an event-by-event basis. The technique allows determination of gamma strength functions, and rotational damping width as a function of spin and temperature. Thus, it opens up the possibility of studying the onset of motional narrowing, order-to-chaos transition, and the mapping of the evolution of nuclear collectivity with spin and temperature. Application of the technique for preferential entry-state population, exit-channel selection, and feeding of the discrete states via selective pathways will be discussed.

Analysis of vibration transmission through periodic structures using a power flow approach

The analysis of the parameters controlling the transmission of vibrational power through coupled structures can be performed using a structural power flow approach. In this paper, a periodic structure is considered with equal length spans between the stiffeners or the supports. With the power flow technique, the global structure is divided into subelements for which structural mobility functions can be defined. Also, structural mobility elements can be introduced at the interfaces between the subelements to represent different types of supports or stiffeners or some other interface characteristic. Thus, using this approach, the influence of such parameters as translational and rotational inertia, stiffness, and damping of the supports or stiffeners, and the stiffness, damping, and other structural characteristics of the separate spans, can be determined using this technique. This approach is applied here to a thin periodic beam with different types of stiffeners and supports, and some of the analysis results are presented. [Work supported by NASA.]

Rotational damping and the spontaneous polarization in ferroelectric liquid crystals

Rotational damping and the spontaneous polarization in ferroelectric liquid crystals

Nuclear rotational damping: Finite-system analogue to motional narrowing in nuclear magnetic resonances.

From the analogy between the collective quadrupole decay among compound nuclear states in strongly rotating nuclei and the phenomenon of nuclear magnetic resonance, it is possible to formulate a model of nuclear rotational damping which exhibits interesting correspondences between nuclear and atomic statistical processes.

Motional narrowing in CO2: a hydrodynamic description?

The motionally narrowed depolarized Raman spectrum of compressed CO2 is reexamined in terms of classical rotational diffusion. The analysis shows that a hydrodynamic interpretation of the width of the spectrum in terms of rotational Brownian motion and viscous damping is not warranted for CO2 and probably not for any single component fluid. The analysis also gives a physical reason for the τ0 arbitrarily introduced by several authors while inflicting a hydrodynamic interpretation on motionally narrowed rotational spectra.

Squeeze Effects in Radial Face Seals

Squeeze effects in a liquid lubricated radial face seal are analyzed. The analysis considers face misalignment with both axial and angular vibrations of the primary seal ring. Translational, rotational, and cross-coupled damping coefficients of the fluid film are derived analytically from a solution of the Reynolds equation utilizing the narrow seal approximation. Results are given for a wide range of practical radius ratios. At each radius ratio, the complete range of angular misalignment—from parallel faces to touch down—is covered. It is shown that squeeze effects in face seals are usually larger than the more familiar hydrodynamic effects. These effects play an important role in the seal’s mechanism of operation and therefore have to be considered in any realistic seal model.

Motion and stability of a rotating space station-cable-counterweightconfiguration

An analysis of the dynamics of a rotating, connected two-body satellite system is presented. The motion is restricted to the orbital plane in which the system mass center follows a circular orbit. The cable is assumed to be extensible, but of negligible mass. The Lagrangian equations of motion are developed and linearized about the equilibrium motion, where the cable tensile force is balanced by the centrifugal force. Necessary and sufficient Routh-Hurwitz stability criteria are obtained for various special cases. Damping system parameters are optimized by repeated examination of the roots of the system characteristic equation. Minimum time constants are found to be insensitive to small changes in the amount of cable damping, but are dependent on the amount of rotational damping of the end body motions. Spin axis drift attributed to gravity-gradient torques is examined quantitatively and found to be small.

Rotational axisymmetric mean flow and damping of acoustic waves in asolid propellant rocket.

Rotational axisymmetric mean flow and damping of acoustic waves in asolid propellant rocket.