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81.
The continuum γ-rays following the reaction 166Er(α, 2n)168Yb have been studied at bombarding energies of 21, 27 and 36 MeV. The shape of the statistical γ-rays below 1 MeV was deduced. A low energy bump at ~300 keV was observed. This may arise from transitions along bands at and above the pairing gap. 相似文献
82.
D. Ward P. Colombani I.Y. Lee P.A. Butler R.S. Simon R.M. Diamond F.S. Stephens 《Nuclear Physics A》1976,266(1):194-214
Rotational states up to spin 20+ (18+) in 174Yb (176Yb) have been Coulomb excited using beams of 136Xe. Lifetimes up to and including the 14+ state have been measured using Doppler-broadened lineshape techniques with 136Xe and 86Kr beams. An annular gas-scintillation counter has been developed in order to perform particle-γ coincidence studies. Moments of inertia in 174, 176Yb behave very regularly, showing no signs of backbending effects. The measured lifetimes are in agreement with the rotational model predictions, and the measured cross sections for Coulomb excitation of the high-spin states are in agreement with the semiclassical Winther-de Boer calculation. 相似文献
83.
Mass-separated samples of 254mEs were used to investigate its α-decay scheme. Twelve α-groups were identified in a spectrum measured with the Argonne magnetic α-spectrometer. The favored α-transition populates a 211.8 keV level in 250Bk and four members of its rotational band were observed. A three-parameter α-γ time coincidence experiment showed that the 211.8 keV level decayed by three routes: two were prompt and one was delayed. The delayed γ-rays (50.07, 71.30, 90.7, 104.0, 126.0 and 175.7 keV) decayed with a 42±2ns half-life. The energies of the prompt γ-rays were 79.90, 96.3, 177.3 and 211.8 keV. From an α-ce? coincidence experiment the multipolarity of the 211.8 keV transition was deduced to be E1. The α-branching was determined from an α-singles spectrum and was found to be 0.33±0.01%. From the results of the present investigation and the known properties of 250Bk and 254mEs, the 211.8 keV state in 250Bk and the 254mEs ground state were given assignment. Other levels in 250Bk were postulated at 104.0 (and its rotational member at 125.3), 131.9 and 175.3 keV and these were given tentative assignments of and (with I = 1), respectively. The splitting energies between the parallel and antiparallel coupled states were calculated with a Gaussian potential for the residual neutron-proton interaction and were found to be in agreement with the experimental values. A precise measurement of the energies and intensities of γ-rays and K X-rays associated with the 254mEs β? decay was also made. The Fm Kα2 and Kα1 energies were found to be 115.280±0.015 and 121.065±0.015 keV, respectively. 相似文献
84.
85.
Stephens FS Deleplanque MA Lee IY Ward D Fallon P Cromaz M Clark RM Diamond RM Macchiavelli AO Vetter K 《Physical review letters》2002,88(14):142501
We have made the first clear measurements of rotational damping widths in nuclei. In a mixture of three Yb nuclei, these widths are 300 +/- 60 keV between 1.2 and 1.5 MeV gamma-ray energy [approximately (37-57)Planck's constant]. Compound damping and motional narrowing are discussed in connection with these results. 相似文献
86.
A sandpile with two stable and two unstable ranges of slopes is presented as a minimal model for the study of H-mode pedestal formation and dynamics. Pedestals are observed to form and expand inward with increasing deposition. Transport bifurcation is not critical to pedestal formation, though the pedestal structure obtained with a second, hard stability boundary is qualitatively different from that found in standard sandpiles. Nonperiodic particle ejection events are observed, but do not initiate pedestal collapse. Pedestal formation alters the spectrum of transport avalanches. 相似文献
87.
We show that the autocorrelation sequence of interarrival times for a Markovian arrival process (MAP) of order two is geometric. We determine the set of feasible values for the autocorrelation decay parameter and the first two or three moments of the interarrival time distribution. A method is derived for matching these parameters to a MAP of order two and some numerical examples are included to illustrate approximating higher dimensional MAPs by two dimensional ones. The numerical examples have helped us pose important questions regarding the significance of correlation in a MAP of order two when it is used as input to a queueing model. 相似文献
88.
We develop and validate an efficient lattice kinetic Monte Carlo (LKMC) method for simulating particle aggregation in laminar flows with spatially varying shear rate, such as parabolic flow or flows with standing vortices. A contact time model was developed to describe the particle-particle collision efficiency as a function of the local shear rate, G, and approach angle, θ. This model effectively accounts for the hydrodynamic interactions between approaching particles, which is not explicitly considered in the LKMC framework. For imperfect collisions, the derived collision efficiency [?=1 - ∫(0)(π/2) sinθ exp(-2cotθΓ(agg)/G)dθ] was found to depend only on Γ(agg)∕G, where Γ(agg) is the specified aggregation rate. For aggregating platelets in tube flow, Γ(agg)=0.683 s(-1) predicts the experimentally measured ε across a physiological range (G = 40-1000 s(-1)) and is consistent with α(2b)β(3)-fibrinogen bond dynamics. Aggregation in parabolic flow resulted in the largest aggregates forming near the wall where shear rate and residence time were maximal, however intermediate regions between the wall and the center exhibited the highest aggregation rate due to depletion of reactants nearest the wall. Then, motivated by stenotic or valvular flows, we employed the LKMC simulation developed here for baffled geometries that exhibit regions of squeezing flow and standing recirculation zones. In these calculations, the largest aggregates were formed within the vortices (maximal residence time), while squeezing flow regions corresponded to zones of highest aggregation rate. 相似文献
89.
Intrermolecular cyclization of 1,3-dipolar aroylnitrile oxides to malononitrile provided a viable approach to a variety of novel (3-aroyl-1,2,4-oxadiazol-5-yl)acetic acid derivatives. 相似文献
90.
H. Hübel M. Murzel E. M. Beck H. Kluge A. Kuhnert K. H. Maier J. C. Bacelar M. A. Deleplanque R. M. Diamond F. S. Stephens 《Zeitschrift für Physik A Hadrons and Nuclei》1988,329(3):289-299
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. 相似文献