Isoscaling behavior studied by HIPSE model

The isoscaling behavior in the reaction system of 58,64Ni + 9Be has been studied by using the heavy-ion phase-space exploration(HIPSE) model. The extracted isoscaling parameters α and β for both heavy and light fragments for HIPSE model calculations are in good agreement with recent experimental data. The investigation shows that the parameters in the HIPSE model have some effect on the isoscaling parameter. The isoscaling parameters for hot and cold fragments have been extracted.     

Isoscaling of projectile-like fragments

In this paper, the isotopic and isotonic distributions of projectile fragmentation products have been simulated by a modified statistical abrasion--ablation model and the isoscaling behaviour of projectile-like fragments has been discussed. The isoscaling parameters α and β have been extracted respectively, for hot fragments before evaporation and cold fragments after evaporation. It looks that the evaporation has stronger effect on α than β. For cold fragments, a monotonic increase of α and β with the increase of Z and N is observed. The relation between isoscaling parameter and the change of isospin content is discussed.     

Isoscaling in Statistical Sequential Decay Model

A sequential decay model is used to study isoscaling, i.e. the factorization of the isotope ratios from sources of different isospins and sizes over a broad range of excitation energies, into fugacity terms of proton and neutron number, R21（N, Z） = Y2（ N, Z）/Y1（ N, Z） = Cexp（αN -βZ）. It is found that the isoscaling parameters α and β have a strong dependence on the isospin difference of equilibrated source and excitation energy, no significant influence of the source size on α andβ has been observed. It is found that α and β decrease with the excitation energy and are linear functions of 1/T and △（Z/A）2 or△（N/A）2 of the sources. Symmetry energy coefticient Gsym is constrained from the relationship of a and source △（Z/A）2, /3 and source △（N/A）2.     

Recrystallization behavior of high-fluence N-implanted GaAs studied by Raman spectroscopy

Raman spectroscopy was used to study the evolution of host lattice recrystallization in high-fluence N⁺-implanted GaAs. A high-fluence of N⁺ ions (>10¹⁵ cm⁻²) was introduced into semi-insulating GaAs by the combinatorial implantation method. Subsequent thermal annealing at 800 °C was carried out to re-grow the implantation-induced amorphous layers. The dependence of Raman parameters on N contents was systematically observed for each recrystallized cell. The volume of the newly formed crystallites with original orientation decreases with increasing fluences, whereas that of crystallites of other orientations increases after high-fluence implantation and annealing. The correlation length L, representing the size of crystalline regions with preserved translational symmetry, was determined by fitting the LO phonon signal with spatial correlation model. For 10¹⁶ cm⁻² implantation, the recrystallized layer consists of nano-meter-sized crystallites (∼30 nm). The dimension of the recrystallized crystallites decreases with increasing N⁺ fluences, in good agreement with the model.     

Critical behavior of a ferroelectric studied by nuclear spin-lattice relaxation

Nuclear spin-lattice relaxation measurements have been performed on ¹¹B nuclei in colemanite CaB₃O₄(OH)₃·H₂O in the ferroelectric and paraelectric phases. Results obtained with a temperature accuracy of 0.01° C show a logarithmic behavior of T₁^?1 in the very vicinity of T_c.     

Bromine metallization studied by X-ray absorption spectroscopy

The experimental data carried out by M?ssbauer and magnetic resonances investigations of the structural phase transitions in K₂ZnCl₄ crystals are discussed by a simple electrostatic model, calculating, the lattice contributions to the local electric potential V(r), electric field intensity E(r) and electric field gradient tensor, (r) and taking into account both the fractional electric point charges and rigid lattice approximations. The validity of the model is proved by a good fit of the computing results and experimental data of quadrupole splitting parameters at K sites obtained by ³⁹K-NMR methods in high temperature incommensurate phase ( Pnam symmetry). The experimental results obtained by M?ssbauer and EPR methods in commensurate phase (Pna2₁ symmetry) of iron and copper doped K₂ZnCl₄ crystals are explained by relaxing the rigid lattice approximation. The insertion of probe ions appear to be done on not-exactly-Zn²⁺ site. Received 3 February 1999 and Received in final form 4 May 1999     

Mn/PbTe(111)界面行为的光电子能谱研究

利用X光电子能谱(XPS)对Mn在PbTe(111)表面上沉积生长的界面性质进行了研究.研究表明Mn的沉积使衬底发生了原子尺度上的突变及金属/半导体界面的形成.从X光电子能谱的芯态能级峰来看,随着Mn膜的沉积Pb 4f峰的低结合能端出现了金属Pb的特征新峰,而Te 3d峰的高结合能端却出现了MnTe特征新峰.且随着Mn膜厚度的增加这些新峰变得越来越明显,当Mn膜厚度超过7 ML(monolayer)(即超过Pb,Te的探测深度)时,衬底信号峰完全消失,只剩下金属Pb和MnTe的芯态能级峰.Mn膜厚度继续增 关键词： PbTe半导体 界面形成 光电子能谱 偏析     

Dependence of Isoscaling Parameters on Nucleon-Nucleon Cross Section and Momentum-Dependent Interaction

Inltuences of the isospin dependence of the in-medium nucleon-nucleon cross section and the momentum-dependent interaction （MDI） on the isotope scaling are investigated by using the isospin-dependent quantum molecular dynamics model （IQMD）. The results show that both the isospin dependence of the in-medium nucleon-nucleon cross section and the momentum-dependent interaction affect the isoscaling parameters appreciably and indepen- dently. The inltuence caused by the isospin dependence of two-body collision is relatively larger than that from the MDI in the mean tield. Aiming at exploring the implication of isoscaling behaviour, which the statistical equilibrium in the reaction is reached, the statistical properties in the mass distribution and the kinetic energy distribution of the fragments simulated by IQMD are presented.     

Degradation behavior of deep UV-LEDs studied by electro-optical methods and transmission electron microscopy

Degradation mechanism of 265-nm deep ultraviolet light emitting diodes (UV-LEDs) has been investigated by means of electroluminescence, current-voltage measurement, capacitance-voltage measurement, and transmission electron microscopy (TEM) equipped with energy dispersive X-ray spectrometer (EDAX). It is revealed that a major degradation mode of UV-LEDs may be the leakage current induced optical degradation. The current pathway is demonstrated by TEM with EDAX, indicating that the contact metals can partially interact with p-type materials, which accelerate the degradation of LEDs. The presented results can help to understand the degradation mechanisms and improve the reliability of deep UV-LEDs.     

Critical behavior of electric field gradient in MnSi studied by muon level-crossing resonance

The electric quadrupole interaction of⁵⁵Mn nuclei was studied in the weakly ferromagnetic system MnSi using muon level-crossing resonance (LCR) technique. The temperature dependence of the electric field gradient (EFG) shows a critical behavior near the ferromagnetic transition temperature, indicating that the EFG due to the conduction electron is strongly correlated with the magnetic susceptibility in the itinerant electron magnetism. The temperature dependence of EFG is in reasonable agreement with the self-consistent renormalization theory developed by Moriya and coworkers.We gratefully acknowledge helpful discussion with Dr. N. Nishida. We also wish to thank Keith Hoyle and Curtis Ballard for technical support.     

Nuclear structure and nuclear moments studied by the shell model and the interacting boson model

Magnetic dipole and electric quadrupole moments are discussed in terms of the interacting boson model (IBM) and the shell model. From the viewpoint of the IBM, systematic variations of magnetic moments will be discussed by analyzing data of Xe and Ba isotopes. Magnetic and quadrupole moments of various states of Sm and Os isotopes are discussed, pointing out an open problem in the magnetic moments of Os isotopes. The importance of measuring the quadrupole moment of O(6) or -unstable nuclei is emphasized by the example of¹²⁸Xe. The structure of neutron-rich unstable nuclei will be studied in terms of the shell model, by paying attention to the break-down of the closed shell structure, for instance, the collapse ofN=20 closed shell withZN=20. The magnetic moment of the anomalous ground state of¹¹Be is another topic of this discussion, and it is studied in terms of a new theoretical framework called variational shell model.     

Stacking behavior of 2-D assemblies of octa-alkoxyl-substituted phthalocyanine studied by scanning tunneling microscopy

In this paper we report the observations of the bilayer structures of octa-alkoxyl-substituted phthalocyanine formed with high stability on graphite surfaces through direct deposition from solutions. The high resolution scanning tunneling microscope (STM) images of the overlayer assembly display discernible shifts. The bilayer structures are simulated by molecular mechanics method and the calculated results agree well with the experimental observations, indicating that the observed overlayer shift could be attributed to the π-π interaction associated with phthalocyanine. The results suggest that the multilayer growth of PcOC8 is jointly affected by π-π interactions, especially together with Van der Waals interactions.     

Mixing in a model gas turbine combustor studied by panoramic optical techniques

Using planar optical methods based on laser-induced fluorescence and particle image velocimetry instantaneous velocity fields and passive tracer concentration are measured simultaneously in a model of GT-combustor at realistic flow rates. Spatial distributions of velocity pulsations and passive tracer concentration pulsations are measured at air flow rate about 0.4 kg/s. Correlations of velocity and concentration pulsations are measured. The most intense turbulent mass flux in the region of swirling flow mixing layer was observed. The contribution of advective and turbulent components in the transfer of a passive tracer in the axial direction was estimated.     

Hydrogen behavior in Pd0.75Ag0.25H x studied by PAC and PAS

Hydrogen behavior in Pd_0.75Ag_0.25H _x has been investigated by both perturbed angular correlation (PAC) and positron annihilation lifetime spectroscopy (PAS) techniques. The PAC measurements with the ¹¹¹Ag/¹¹¹Cd probe nuclei were conducted at room temperature as a function of the hydrogen concentration x up to 0.35. At x = 0 the probe nuclei experienced no quadrupole perturbation, while a distinct perturbation was observed after hydrogen charging. The quadrupole interaction frequency ω ₁ and its distribution width σ ₁ and relative fraction f₁ all decrease with increasing hydrogen concentration, indicating size growth and concentration reduction of the hydrogen induced vacancy clusters. The measured frequency distribution width σ ₁ reveals hydrogen diffusion. The PAS measurements were also performed at room temperature. The obtained lifetimes and their variation with hydrogen concentration strongly support the PAC results. The experimental results can be explained by the appearance of the β-phase in the Pd_0.75Ag_0.25H _x samples. The α-phase is the major phase in the Pd_0.75Ag_0.25H _x samples. Charging of the hydrogen leads to the formation of the β-phase and the fraction of the β-phase increases with increasing hydrogen concentration. The present PAC and PAS results show that as the fraction of the β-phase increases, hydrogen induced vacancy clusters are formed and become larger and larger, while the cluster density reduces due to the combination of the vacancy clusters into larger size vacancy clusters.     

Density and Symmetric Potential Dependences of Isoscaling Behaviour in the Lattice Gas Model

Isoscaling behaviour of the statistical emission fragments from the equilibrated sources with Z=30 and N=30, 33, 36 and 39 is investigated in the framework of the isospin-dependent lattice gas model. The dependences of isoscaling parameters α on source isospin asymmetry, temperature andfreeze-out density are studied, and the `symmetry energy' is deduced from isoscaling parameters. The results show that symmetry energy C_sym is insensitive to the change of temperature but follows the power-law dependence on the freeze-out density ρ. The effect of strength of asymmetry of nucleon--nucleon interaction potential on the density dependence of the symmetry energy is discussed.     

Abnormal odd-even staggering behavior around 132Sn studied by density functional theory

In this work, we have performed Skyrme density functional theory (DFT) calculations of nuclei around ¹³²Sn to study whether the abnormal odd-even staggering (OES) behavior of binding energies around N = 82 can be reproduced. With the Skyrme forces SLy4 and SkM*, we tested the volume- and surface-type pairing forces and also the intermediate between these two pairing forces, in the Hartree-Fock-Bogoliubov (HFB) approximation with or without the Lipkin-Nogami (LN) approximation or particle number projection after the convergence of HFBLN (PLN). The Universal Nuclear Energy Density Function (UNEDF) parameter sets are also used. The trend of the neutron OES against the neutron number or proton number does not change significantly by tuning the density dependence of the pairing force. Moreover, for the pairing force that is favored more at the nuclear surface, a larger mass OES is obtained, and vice versa. It appears that the combination of volume and surface pairing can give better agreement with the data. In the studies of the OES, a larger ratio of surface to volume pairing might be favored. Additionally, in most cases, the OES given by the HFBLN approximation agrees more closely with the experimental data. We found that both the Skyrme and pairing forces can influence the OES behavior. The mass OES calculated by the UNEDF DFT is explicitly smaller than the experimental one. The UNEDF1 and UNEDF2 forces can reproduce the experimental trend of the abnormal OES around ¹³²Sn. The neutron OES of the tin isotopes given by the SkM* force agrees more closely with the experimental one than that given by the SLy4 force in most cases. Both SLy4 and SkM* DFT have difficulties in reproducing the abnormal OES around ¹³²Sn. Using the PLN method, the systematics of OES are improved for several combinations of Skyrme and pairing forces.     

Ground-state complex formation of perylene with pyromellitic dianhydride studied by static fluorescence quenching

The association of complex formation with static quenching in CT systems was investigated. Evaluation of the data made evident that the inner filter effect must be allowed for. Time-resolved and temperature-dependent stationary measurements of fluorescence led to the separation of dynamic and static quenching components. The static quenching constant is discussed with respect to the equilibrium constant of complex formation determined by absorption spectroscopy.