Search Results (211 total)

The higher spin levels in neutron-rich ¹⁰⁴Nb have been investigated from a study of the prompt γ rays in spontaneous fission of ²⁵²Cf with the Gammasphere detector array. A new collective band has been identified for the first time. This band is proposed as a semidecoupled band based on the configuration π5/2^-[303]⊗ν1/2^-[541]. The other structural characteristics are discussed.

The high spin excited states of neutron-rich nuclei ¹⁵⁹Sm and ^89,91Kr are identified for the first time from the spontaneous fission of ²⁵²Cf. Six excited states and six γ transitions in ¹⁵⁹Sm are reported here for the first time. Five and two new γ transitions are identified in ⁸⁹Kr and ⁹¹Kr, respectively. Level schemes in ^89,91Kr are interpreted as the 2d_5/2 neutron hole configuration weakly coupled to the neighboring even-even Kr nuclei. A possible yrast spin sequence of 11/2^--9/2⁺-5/2⁺ is suggested in ⁸⁹Kr. A rotational band with the proposed configuration of ν5/2[523] is observed in ¹⁵⁹Sm.

Neutron-rich nuclei of ^153,155Nd were studied from the spontaneous fission of ²⁵²Cf. Eleven and nine new γ transitions were identified in ¹⁵³Nd and ¹⁵⁵Nd, respectively. Rotational bands with the configurations of ν5/2[642] and ν3/2[521] were identified in ¹⁵³Nd and ¹⁵⁵Nd, respectively. Excited states and γ transitions in ¹⁵⁵Nd are reported for the first time here.

The high-spin spectroscopy of neutron-rich ¹⁰⁹Ru is studied by measuring the prompt γ rays from the spontaneous fission fragments of ²⁵²Cf with 102 Compton-suppressed Ge detectors in the Gammasphere detector array. Previous band structures are confirmed and the ground state band is extended. A positive parity band based on a 332.5 keV level is newly identified. This band is proposed as a single-neutron excitation band built on the 7/2⁺[404] Nilsson orbital. Some band structural characteristics are discussed.

This paper is concerned with the connection between the properties of dielectric relaxation and alternating-current (ac) conduction in disordered dielectrics. The discussion is divided between the classical linear-response theory and a self-consistent dynamical modeling. The key issues are stretched exponential character of dielectric relaxation, power-law power spectral density, and anomalous dependence of ac conduction coefficient on frequency. We propose a self-consistent model of dielectric relaxation in which the relaxations are described by a stretched exponential decay function. Mathematically, our study refers to the expanding area of fractional calculus and we propose a systematic derivation of the fractional relaxation and fractional diffusion equations from the property of ac universality.

The high-spin levels in the neutron-rich ¹⁴³La nucleus have been investigated from the study of prompt γ rays in the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. A new level scheme with spin up to 27/2 ħ has been established, and the collective bands have been identified for the first time. A set of opposite-parity bands connected by ΔI=1E1 crossing transitions gives evidence for octupole correlations. The results of B(E1)/B(E2) branching ratios indicate that the octupole correlations in ¹⁴³La are strong. The reflection-asymmetry shell model is applied to calculate the levels of the octupole bands of ¹⁴³La, and the calculated results are in good agreement with the experimental ones.

High spin states of ^137,138Cs have been studied by measuring γ-γ-γ coincidences from the spontaneous fission of ²⁵²Cf with the LBNL Gammasphere detector array. The high spin level scheme of the N=83 neutron-rich Cs (Z=55) isotope, ¹³⁸Cs, built on the 6^- isomeric state, has been established for the first time up to a 4626 keV level, assigned (16⁺). The level scheme of ¹³⁷Cs has been expanded up to a 5495 keV level, assigned (31/2^-). Spins, parities, and configurations are assigned based on the agreement between experimental level energies and shell model calculations and level systematics. Similarities are observed in the N=82 isotones, ¹³⁷Cs and ¹³⁵I, up to 17/2⁺ as well as in the N=83 isotones, ¹³⁸Cs and ¹³⁶I, up to 12^-. The shell model calculations indicate the important role played by interactions between the excitation of the valence protons outside the Z=50 major shell and the f_7/2 valence neutron outside the N=82 major shell.

High-spin band structures in neutron-rich ¹⁰⁵Mo have been investigated by measuring prompt γ rays emitted by the spontaneous fission fragments of ²⁵²Cf with the Gammasphere detector array. The yrast band has been confirmed and five new collective bands are observed. The three bands based on the 246.3-, 332.0-, and 310.0-keV levels are proposed as the single-neutron excitation bands built on the 3/2⁺[411], 1/2⁺[411], and 5/2⁺[413] Nilsson orbitals, respectively. The other two bands with band head levels at 870.5 and 1534.6 keV are candidates for one-phonon K=9/2 and two-phonon K=13/2 γ-vibrational bands, respectively. Systematic comparison of these bands with bands in neighboring nuclei are discussed.

The high-spin nuclear structure of Tc isotopes is extended to more neutron-rich regions based on the measurements of prompt γ rays from the spontaneous fission of ²⁵²Cf at the Gammasphere. The high-spin level scheme of N=67 neutron-rich ¹¹⁰Tc (Z=43) is established for the first time, and that of ¹¹¹Tc is extended and expanded. The ground band of ¹¹¹Tc reaches the band-crossing region, and the new observation of the weakly populated α=-1/2 member of the band provides important information on signature splitting. The systematics of band crossings in the isotopic and isotonic chains and a CSM calculation suggest that the band crossing of the ground band of ¹¹¹Tc is due to alignment of a pair of h_11/2 neutrons. The best fit to signature splitting, branching ratios, and excitations of the ground band of ¹¹¹Tc by the rigid triaxial rotor plus particle model calculations result in a shape of ɛ₂=0.32 and γ=-26^° for this nucleus. Its triaxiality is larger than that of ^107,109Tc, which indicates increasing triaxiality in Tc isotopes with increasing neutron number. The identification of the weakly populated K+2 satellite band provides strong evidence for the large triaxiality of ¹¹¹Tc. In ¹¹⁰Tc, the four lowest-lying levels observed are very similar to those in ¹⁰⁸Tc. At an excitation of 478.9 keV above the lowest state observed, ten states of a ΔI=1 band are observed. This band of ¹¹⁰Tc is very analogous to the ΔI=1 bands in ^106,108Tc, but it has greater and reversal signature splitting at higher spins.

Triple coincidence data from the fission of ²⁵²Cf were used to deduce the intensity of the proposed “hot” mode in barium channels. γ-γ-γ and α-γ-γ fission data were analyzed to find the neutron multiplicity distribution for several binary and ternary charge splits. The binary channels Xe-Ru and Ba-Mo were analyzed, as well as the Ba-α-Zr, Mo-α-Xe, and Te-α-Ru ternary channels. An improved method of analysis was used to avoid many of the complexities associated with fission spectra. With this method, we were unable to confirm the second mode in the either the Ba-Mo or Ba-α-Zr splits.

Eight new high spin states and 23 new γ transitions have been identified in ¹⁰⁰Zr from studies of ²⁵²Cf spontaneous fission with Gammasphere. A near-spherical excited band in ¹⁰⁰Zr based on the 331.1 keV 0⁺ state is extended from 4⁺ up to 12⁺. A ΔI=1 band with band-head energy of 2316.1 keV is extended.

New transitions and levels in ¹⁴⁸Ce have been observed in a γ-γ-γ coincidence study from the spontaneous fission of ²⁵²Cf with Gammasphere detector array. The ground band has been extended up to I^π=22⁺, and side bands are extended with ΔI=2 stretched transitions and ΔI=1 crossing transitions. The observed level scheme is interpreted in terms of possible octupole correlations. Two sets of interwined positive- and negative- parity bands with the simplex quantum numbers s=±1 are suggested. The results of B(E1)/B(E2) branching ratios indicate that the octupole correlations in ¹⁴⁸Ce are strong.

Viscoelastic vortical fluid motion in a strongly coupled particle system has been observed experimentally. Optical tracking of particle motion in a complex plasma monolayer reveals high grain mobility and large scale vortex flows coexistent with partial preservation of the global hexagonal lattice structure. The transport of particles is superdiffusive and ascribed to Lévy statistics on short time scales and to memory effects on the longer scales influenced by cooperative motion. At these longer time scales, the transport is governed by vortex flows covering a wide spectrum of temporal and spatial scales.

From the analysis of γ-γ-γ coincidence data taken with Gammasphere of the prompt γ rays in the spontaneous fission of ²⁵²Cf, the 2⁺→0⁺ transition in ⁸⁸Se was identified for the first time. Also, the 4⁺→2⁺ and 6⁺→4⁺ transitions in ⁸⁶Se were identified along with four new states above 4⁺ in ⁸⁴Se. Surprisingly, the 2⁺ energy rises in ⁸⁸Se compared to ⁸⁶Se. This increase in energy could arise from the interaction of a low-lying excited 0⁺ state with different deformation and the 0⁺ ground state to depress the ground-state energy.

Level structures of ^113,115,117Pd have been studied using the Gammasphere and a spontaneous fission source of ²⁵²Cf. A new 85.1-keV transition was identified in ¹¹³Pd. This indicates that the spin and parity of the isomeric state is 9/2^- rather than the previously assigned 11/2^-. New low-energy transitions are confirmed in ^115,117Pd. In ¹¹⁵Pd, the 39.0.- and 49.0-keV transitions are shown to be in prompt coincidence. This coincidence relationship indicates a spin and parity assignment of 1/2⁺ for the ground state rather than the previously assigned 3/2⁺.

The effect of attractive linear potentials on self-focusing in-waves modeled by a nonlinear Schrödinger equation is considered. It is shown that the attractive potential can prevent both singular collapse and dispersion that are generic in the cubic Schrödinger equation in the critical dimension 2 and can lead to a stable oscillating beam. This is observed to involve a splitting of the beam into an inner part that is oscillatory and of subcritical power and an outer dispersing part. An analysis is given in terms of the rate competition between the linear and nonlinear focusing effects, radiation losses, and known stable periodic behavior of certain solutions in the presence of attractive potentials.

New level schemes of odd-Z ^105,107,109Tc are proposed based on the ²⁵²Cf spontaneous-fission-gamma data taken with Gammasphere in 2000. Bands of levels are considerably extended and expanded to show rich spectroscopic information. Spin/parity and configuration assignments are made based on determinations of multipolarities of low-lying transitions and the level analogies to the previously reported levels, and to those of the neighboring Rh isotopes. A non-yrast negative-parity band built on the 3∕2⁻[301] orbital is observed for the first time in ¹⁰⁵Tc. A positive-parity band built on the 1∕2⁺[431] intruder orbital originating from the π(g_7∕2∕d_5∕2) subshells and having a strong deformation-driving effect is observed for the first time in ¹⁰⁵Tc, and assigned in ¹⁰⁷Tc. A positive-parity band built on the excited 11∕2⁺ level, which has rather low excitation energy and predominantly decays into the 9∕2⁺ level of the ground state band, provides evidence of triaxiality in ^107,109Tc, and probably also in ¹⁰⁵Tc. Rotational constants are calculated and discussed for the K=1∕2 intruder bands using the Bohr-Mottelson formula. Level systematics are discussed in terms of the locations of proton Fermi levels and deformations. The band crossings of yrast positive-parity bands are observed, most likely related to h_11∕2 neutron alignment. Triaxial-rotor-plus-particle model calculations performed with ε=0.32 and γ=−22.5° on the prolate side of maximum triaxiality yielded the best reproduction of the excitation energies, signature splittings, and branching ratios of the positive-parity bands (except for the intruder bands) of these Tc isotopes. The significant discrepancies between the triaxial-rotor-plus-particle model calculations and experiment for the K=1∕2 intruder bands in ^105,107Tc need further theoretical studies.

Twenty new γ transitions in ⁹⁵Sr were identified from γ-γ-γ coincidences in the spontaneous fission of ²⁵²Cf. New bands, based on a previously known isomeric state, T_1∕2=23.6(24) ns, have been built up to a (31∕2⁺) state. The states in these bands show a close similarity in transition energies to the ground band of the neighboring ⁹⁴Sr, which has a spherical shape. This similarity is interpreted as the weak coupling of the 1g_7∕2 neutron particle to the levels of the ₃₈⁹⁴Sr₅₆ core.

Half-lives (T_1∕2) of several states which decay by delayed γ transitions were determined from time-gated triple γ coincidence method. We determined, for the first time, the half-life of 330.6+x state in ¹⁰⁸Tc and the half-life of 19∕2⁻ state in ¹³³Te based on the new level schemes. Three half-lives of ⁹⁹Zr, ¹³⁴Te, and ¹³⁷Xe are consistent with the previously reported ones. These results indicate that this new method is useful for measuring the half-lives.

Ternary fission of ²⁵²Cf was studied at Gammasphere with eight ΔE×E particle telescopes. After Doppler correction, the 3368  keV  2⁺→0⁺ transition in ¹⁰Be was found in coincidence with the ¹⁰Be fragments with no evidence for any γ rays not Doppler shifted for ¹⁰Be with >21  MeV kinetic energy. The ratio of the first 2⁺ to ground-state population probabilities was estimated as N(2⁺)∕N(0⁺)=0.160±0.025. The angular distribution for 3368  keV γ rays indicated the spin alignment of excited ¹⁰Be nuclei preferentially is parallel or antiparallel to their momentum.

Two-dimensional fluid simulations of interchange turbulence for geometry and parameters relevant for the scrape-off layer of magnetized plasmas are presented. The computations, which have distinct plasma production and loss regions, reveal bursty ejection of particles and heat from the bulk plasma in the form of blobs. These structures propagate far into the scrape-off layer where they are dissipated due to transport along open magnetic field lines. From single-point recordings it is shown that the blobs have asymmetric conditional wave forms and lead to positively skewed and flattened probability distribution functions. The radial propagation velocity may reach one-tenth of the sound speed. These results are in excellent agreement with recent experimental measurements.

Level schemes of ¹¹¹Rh and ¹¹³Rh are proposed from the analysis of γ-γ-γ coincidence data from a ²⁵²Cf spontaneous fission source with Gammasphere. These schemes have the highest excitation energies and spins yet established in these nuclei, as well as weakly populated bands not reported in earlier fission-γ work. From these data, information on shapes is inferred. By analogy with lighter Z=45 odd-even isotopes, tentative spins and parities are assigned to members of several rotational bands. In this region triaxial nuclear shapes are known to occur, and we carried out calculations for ¹¹¹Rh and ¹¹³Rh with the triaxial-rotor-plus-particle model. The 7∕2⁺πg_9∕2 bands of both nuclei, as well as lighter isotopes studied by others, show similar signature splitting. Our model calculations give a reasonable fit to the signature splitting, collective sidebands, and transition probabilities at near-maximum triaxiality with γ≈28°. For the K=1∕2⁺[431] band, experiment and model calculations do not fit well, which is accounted for by greater prolate deformation of the K=1∕2⁺ band, a case of shape coexistence. Our data on ^110,112Rh show no backbending and thus support the idea of the band crossing in the ground band of the odd-A neighbors being due to alignment of an h_11∕2 neutron pair. In ^111,113Rh above the band crossing (spins ≈21∕2ℏ) the ground band appears to split, with two similar branches. We consider the possibility that chiral doubling may be involved, but there are not enough levels to determine that.

Incompressible, inviscid, irrotational, unsteady flows with circulation Γ around a distorted toroidal bubble are considered. A general variational principle that determines the evolution of the bubble shape is formulated. For a two-dimensional (2D) cavity with a constant area A, exact pseudodifferential equations of motion are derived, based on variables that determine a conformal mapping of the unit circle exterior into the region occupied by the fluid. A closed expression for the Hamiltonian of the 2D system in terms of canonical variables is obtained. Stability of a stationary drifting 2D hollow vortex is demonstrated, when the gravity is small, gA^3/2/Γ²≪1. For a circulation-dominated regime of three-dimensional flows a simplified Lagrangian is suggested, inasmuch as the bubble shape is well described by the center line R(ξ,t) and by an approximately circular cross section with relatively small area, A(ξ,t)≪(∮|R^′|dξ)². In particular, a finite-dimensional dynamical system is derived and approximately solved for a vertically moving axisymmetric vortex ring bubble with a compressed gas inside.

We present experiments and theory for the “bathtub vortex,” which forms when a fluid drains out of a rotating cylindrical container through a small drain hole. The fast down-flow is found to be confined to a narrow and rapidly rotating “drainpipe” from the free surface down to the drain hole. Surrounding this drainpipe is a region with slow upward flow generated by the Ekman layer at the bottom of the container. This flow structure leads us to a theoretical model similar to one obtained earlier by Lundgren [J. Fluid Mech. 155, 381 (1985)], but here including surface tension and Ekman upwelling, comparing favorably with our measurements. At the tip of the needlelike surface depression, we observe a bubble-forming instability at high rotation rates.

New levels in the neutron-rich ¹¹³Ru nucleus have been identified by analyzing γ-γ-γ coincidence events following the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. A rotational band going up to 3.6 MeV is identified and is proposed to be built on the intruder νh_11/2 orbital going up to (31/2)ħ. A few states of a possible signature partner are also observed.