Anisotropic spin transport in two-terminal mesoscopic rings: Rashba and Dresselhaus spin-orbit interactions

We theoretically investigate the spin transport in two-terminal mesoscopic rings in the presence of both the Rashba spin-orbit interaction (RSOI) and the Dresselhaus spin-orbit interaction (DSOI). We find that the interplay between the RSOI and DSOI breaks the original cylindric symmetry of the mesoscopic rings and consequently leads to the anisotropic spin transport, i.e., the conductance is sensitive to the positions of the incoming and outgoing leads. The anisotropic spin transport can survive even in the presence of disorder caused by impurity elastic scattering in a realistic system.

Luminosity determination for the dd→αK+K-experiment atANKE/COSY

High resolution studies of a0/f0(980) decays into channels involving open strangeness are currently being performed at COSY-Jülich. As a “filter” for isospin-zero intermediate states, i.e. to selectively produce the f0(980) resonance, the dd→αK+K− reaction was measured with the magnetic ANKE spectrometer. In order to determine the luminosity of this experiment, the elastically and quasi-elastically scattered deuterons were recorded simultaneously with the αK+K− events. Here we report about the luminosity determination via investigating the (quasi-) elastic deuterons at ANKE.

Exotic behaviour of angular dispersion of weakly bound nucleus F-17 at small angles

The differential cross sections of F-17 and O-17 elastic scattering products on Pb-208 have been measured at the Radioactive Ion Beam Line at Lanzhou (RIBLL). Two angular dispersion plots of ln(d sigma/d theta) versus theta 2 are obtained from the angular distribution of the elastic scattering differential cross sections. The angular dispersion plot exhibits a clear turning point for F-17 in the range of small scattering angles 6 degrees-20 degrees due to its exotic structure, but for O-17, the turning point is not observed in the same angular range. The experimental results have been compared with previous data of other groups. Systematical analysis on the available data supports the above conclusion that there is an exotic behaviour of the angular dispersion plot of weakly bound nuclei with halo or skin structure as compared with that of the ordinary nuclei near stable line. Therefore the turning point of the angular dispersion plot appears at small angle for weakly bound nuclei with halo or skin structure, and can be used as a new probe to investigate the halo and skin phenomena of weakly bound nuclei.

Study of unbound nuclei N-11 resonance energy level

The excitation functions of elastic scattering proton which were measured with inverse kinematics of elastic resonance scattering reactions in GANIL and MSU have been fitted by the multi-energy level R-matrix theory. The final result shows that the new energy levels order for nucleus N-11 should be 1/2(+), 1/2(-), 5/2(+), 3/2(+), 3/2(-), 5/2(+), 7/2(-), which is consistent with the experimental results of Be-11 (the mirror nucleus of N-11) and the theoretical calculation of N-11 with GCM theory.

Evidence of strong projectile-target-core interaction in single ionization of neon by electron impact

The momentum distributions of recoil ions were measured in the single ionization of neon by electron impact at incident energies between 80 and 2300 eV. It was found that there are a noticeable number of recoil ions carrying large momenta, and the relative contributions of these ions becomes more pronounced with the further decrease of incident electron energy. These observed behaviors indicate that there is a strong projectile-target-core interaction in the single-ionization reaction. By comparing our results with those of electron-neon elastic scattering, we concluded that the elastic scattering of the projectile electron on the target core plays an important role at low and intermediate collision energies.

17F和18Ne与质子弹性散射研究

论文讲述了采用逆运动学方法用放射性核束~(17)F和~(18)Ne与质子弹性散射的实验准备、设汁方法、实验情况、实验数据处理过程、理论分析处理和得到的结果。弹性散射测量核敞射的角分布，对位置探测器有很高的要求。在实验的准备阶段，为了对放射性核束的准确定位，研制了位置分辨为lITlm的高位团置分辨的PPAC。山于质予的穿透能力很强，在半导体硅探测器中的能损很小，实验前，刘。测量反冲质子的探测器PSSD在低能量沉积下的工作情况进行了测试，满足质f位置和I能量测量的要求。实验采用初级束流强度约为80nA能量为45Mev／A的~(20)Ne轰击lmm厚的~9Be，反应产物经过500μm厚的Wedge~(27)Al，通过次级束流线的筛选，得到~(17)F和~(18)Ne和少量的~(16)O束流，其能量分别为17.7Mev／A、16.1Mev／A和14.3Mev／A。然后轰击60μm厚的(CH_2)_n靶。用次级束流线装置的两个焦点处的塑料闪烁体测量放射性核束的时间Tl和T2，根据飞行时间差在相同的磁场条件下来鉴别粒子和得到放射性核束的能量。用靶前的两个PPAC和靶后的一个PPAC来确定放射性核束的入射方向、反应点和出射方向，反冲质子的位置由分布于各实验室系角区的五个PSSD来测定。实验数据处理时，根据放射性核束经过基本相同的飞行路径和磁场条件，用T1和T2测到的飞行时间差来确定放射性核束的能量。将入射到PPAC上的弹核粒子位置，经对宏观几何位置矫正后，来确定弹核粒子的入射方向、反应点位置和出射方向。将PSSD测量到的位置谱经与沉积能量相关的修正因子对位置修正后，确定反冲核在PSSD上的几何位置点，跟PPAC测量确定的靶上的反应点位置结合，确定反冲核的出射方向。测量得到的位置经过空间关系换算，由测量到的弹核入射方向、反应点位置和反冲核出射方向，得到弹性散射的实验室系散射角。累计所有测到的事件得到初始的反冲核实验测量角分布。采用逐个事件的方法，用一事先产生的一系列点组成的数据库模拟探测器边界，事件的几何探测效率进行归一化，得到实际的实验室系散射角分布。用弹核出射角度随反冲核的出射角度的运动学关系鉴别来自靶中的H和C的散射事件。将实验室系角分布转换到质心系下后，再根据弹核粒子数、单位面积靶核数和测量到的事件数，得到实验测量的质的弹性散射微分截面。实验得到的微分截面数据采用零程相互作用的扭曲波玻恩近似理论计算程序DWUCK4序进行光学势拟合计算，选用较准确描述奇异核性质的CH89参数化的光学势为初始的光学势参数，对光学势参数的组成成分进行敏感性分析后，确定参数搜索的顺序，用跟各参数相关联的自动参数搜索程序ABOD进行分析处理。进行光学模型的理论拟合计算时，将计算结果和实验值进行比较，拟合实验数据，求得光学势参数。参数拟合佳度用残差平方和检验(χ~2检验)。得到~(17)F和~(18)Ne与质子弹性散射的光学势参数。根据得到的光学势参数进行折叠模型分析。得到了，1)~(17)F和~(18)Ne实势相互作用均方根半径分别为，_(rF)~(1/2) = 3．239(fm)，_(r_Ne)~(1/2) = 3.317 (fm)。跟相对论平均场计算结果比较分析表明，~(17)F的核物质半径为2.95±0.03fm，~(18)Ne的核物质半径为3.07±0.03fm,~(17)F和~(18)Ne表面的密度要比相对论平均场理论预言的值要大。2)~(17)F和~(18)Ne的自旋轨道耦合相互作用主要作用于核表面区域，这是因为位于核外层的价质子的影响。

The eigenphase formulation of fine-structure transition cross sections

The eigenphase formulation of Blatt and Biedenharn is applied to fine-structure transitions in *P atoms colliding with ‘S perturbers. Consideration is given to the limit of weak spin-orbit interaction. If the eigenphases are equal to the phaseshifts for elastic scattering by the molecular potentials then the expression for the total cross section reduces to the expression derived in the elastic approximation. However, a numerical comparison for the Li(2p ’P) + He(’S) system shows that the elastic molecular phaseshifts are not good approximations to the eigenphases. Hence the elastic approximation cannot be reliable.

Electron/positron collisions with positronium

We report results for e(+/-)-Ps(Is) scattering in the energy range up to 80 eV calculated in 9-state and 30-state coupled pseudostate approximations. Cross-sections are presented for elastic scattering, ortho-para conversion, discrete excitation, ionization and total scattering. Resonances associated with the Ps(n = 2) threshold are also examined and their positions and widths determined. Very good agreement is obtained with the variational calculations of Ward et al. [J. Phys. B 20 (1987) 127] below 5.1 eV. (C) 2004 Elsevier B.V. All rights reserved.

Low-energy positron interactions with atoms and molecules

This paper is a review of low-energy positron interactions with atoms and molecules. Processes of interest include elastic scattering, electronic and vibrational excitation, ionization, positronium formation and annihilation. An overview is presented of the currently available theoretical and experimental techniques to study these phenomena, including the use of trap-based positron beam sources to study collision processes with improved energy resolution. State-resolved measurements of electronic and vibrational excitation cross sections and measurement of annihilation rates in atoms and molecules as a function of incident positron energy are discussed. Where data are available, comparisons are made with analogous electron scattering cross sections. Resonance phenomena, common in electron scattering, appear to be less common in positron scattering. Possible exceptions include the sharp onsets of positron-impact electronic and vibrational excitation of selected molecules. Recent energy-resolved studies of positron annihilation in hydrocarbons containing more than a few carbon atoms provide direct evidence that vibrational Feshbach resonances underpin the anomalously large annihilation rates observed for many polyatomic species. We discuss open questions regarding this process in larger molecules, as well as positron annihilation in smaller molecules where the theoretical picture is less clear.

Ultracold radiative charge transfer in hybrid ion-atom traps

We present ab initio quantum chemistry calculations for elastic scattering and the radiative charge transfer reaction process and collision rates for trapped ytterbium ions immersed in a quantum degenerate rubidium vapor.
The collision of the ion (or ions) with the quasiatom is the key mechanism to transfer quantum coherences between the systems. We use first-principles
quantum chemistry codes to obtain the potential surfaces and coupling terms for the two-body interaction of Yb^+ with Rb. We find that the low energy collision has an inelastic radiative charge transfer process in agreement with recent experiments.
The charge transfer cross section agrees well with the semiclassical Langevin model at higher energies but is dominated by resonances at submillikelvin temperatures.

Oxygen precipitation in Czochralski grown silicon heat treated at 525 degrees C

The diffusion of interstitial oxygen In silicon at 525 degrees C is studied using time-of-flight small-angle neutron scattering (SANS) to separate the elastic scattering from oxygen-containing aggregates from the inelastic scattering from neutron-phonon interactions. The growth of oxygen-containing aggregates as a function of time gives a diffusion coefficient, D, calculated from Ham's theory, that is I factor of similar to 3.8 +/- 1.4 times higher than that expected by extrapolation of higher and lower temperature data (D = 0.13 exp(-2.53 eV kT(-1)) cm(2) s(-1)). This result confirms previous observations of enhanced diffusion at intermediate temperatures (400 degrees C-650 degrees C) although the magnitude of the enhancement we find is Much smaller than that reported by some others.

GLUON SATURATION AND THE FROISSART BOUND: A SIMPLE APPROACH

At very high energies we expect that the hadronic cross sections satisfy the Froissart bound, which is a well-established property of the strong interactions. In this energy regime we also expect the formation of the Color Glass Condensate, characterized by gluon saturation and a typical momentum scale: the saturation scale Q(s). In this paper we show that if a saturation window exists between the nonperturbative and perturbative regimes of Quantum Chromodynamics (QCD), the total cross sections satisfy the Froissart bound. Furthermore, we show that our approach allows us to described the high energy experimental data on pp/p (p) over bar total cross sections.

FUSION ENHANCEMENT/SUPPRESSION AND IRREVERSIBILITY IN REACTIONS INDUCED BY WEAKLY BOUND NUCLEI

We show that halo effects enhance fusion cross sections of weakly bound systems, comparing with the situation when there is no-halo. We introduce dimensionless fusion functions and energy variable quantity to investigate systematical trends in the fusion cross sections of weakly bound nuclei at near-barrier energies. We observe very clearly complete fusion suppression at energies above the barrier due to dynamic effects of the breakup on fusion. We explain this suppression in terms of the repulsive polarization potential produced by the breakup.

CLUSTER MODEL FOR REACTIONS INDUCED BY WEAKLY BOUND AND/OR EXOTIC HALO NUCLEI WITH MEDIUM-MASS TARGETS

An experimental overview of reactions induced by the stable, but weakly-bound nuclei (6)Li, (7)Li and (9)Be, and by the exotic, halo nuclei (6)He, (8)B, (11)Be and (17)F On medium-mass targets, such as (58)Ni, (59)Co or (64)Zn, is presented. Existing data on elastic scattering, total reaction cross sections, fusion, breakup and transfer channels are discussed in the framework of a CDCC approach taking into account the breakup degree of freedom.

Astrophysical S factors for fusion reactions involving C, O, Ne, and Mg isotopes

Using the Sao Paulo potential and the barrier penetration formalism we have calculated the astrophysical factor S(E) for 946 fusion reactions involving stable and neutron-rich isotopes of C, O, Ne, and Mg for center-of-mass energies E varying from 2 to approximate to 18-30 MeV (covering the range below and above the Coulomb barrier). We have parameterized the energy dependence, S(E), by an accurate universal 9-parameter analytic expression and present tables of fit parameters for all the reactions. We also discuss the reduced 3-parameter version of our fit which is highly accurate at energies below the Coulomb barrier, and outline the procedure for calculating the reaction rates. The results can be easily converted to thermonuclear or pycnonuclear reaction rates to simulate various nuclear burning phenomena, in particular, stellar burning at high temperatures and nucleosynthesis in high density environments. (C) 2010 Elsevier Inc. All rights reserved