Calculation of differential Cross Section for pion absorption on diproton

The asymmetry of the differential cross section for the process of pion absorption onT=1 nucleon pairs in³He and³H is calculated using the experimental partial amplitudes for pion scattering prior to the absorption. The asymmetry is found to be a consequence of the even and odd partial-wave interference.     

Measurement of the absolute n p scattering differential cross section at 194 MeV

We describe a double-scattering experiment with a novel tagged neutron beam to measure differential cross sections for np backscattering to better than +/-2% absolute precision. The measurement focuses on angles and energies where the cross section magnitude and angle dependence constrain the charged pion-nucleon coupling constant, but existing data show serious discrepancies among themselves and with energy-dependent partial-wave analyses. The present results are in good accord with the partial-wave analyses, but deviate systematically from other recent measurements.     

Elastic scattering of an electron on the Coulomb potential with a cut-off

The partial-wave method is used to study the elastic scattering of electrons on the Coulomb potential with a cut-off. There is considerable discrepancy between the present results and those obtained by means of the Born approximation and the classical method. At a given specific energy, the cross section exhibits a maximum. This due to the appearance of maxima in the differential cross section in both the forward and the backward direction.     

激发态Li原子和基态Ar原子的相互作用势及低能弹性碰撞

在MRCI+Q/ang-cc-PCVQZ+DK理论基础上对LiAr第一激发态(A²Π)的势能曲线进行了理论计算, 采用HFD(Hartree-Fock dispersion)解析势能函数对得到的势能曲线进行拟合, 并得到了相应的光谱常数, 计算结果与实验值和大部分理论计算值符合得很好. 通过求解核运动的薛定谔方程完整地获得了每个电子态下J=0时的振动能级E_v、转动惯量B_v和6 个离心畸变常数(D_v, H_v, L_v, M_v, N_v, O_v). 然后采用分波法研究了低温及极低温度下激发态Li原子和基态Ar原子沿LiAr相互作用势的弹性碰撞, 在1.0×10^{- 12} –3.45×10^-6 eV碰撞能区内通过数值计算得到了这一弹性碰撞的总截面和各分波截面, 讨论了各分波截面对总截面的影响. 结果表明: 在入射能量低于10^-9 eV时弹性散射的总截面值很大且几乎为一常数, 总弹性截面的形状主要由s分波决定, 但是随着碰撞能量的增加, s分波对总截面的贡献不断减少, 高阶分波对散射截面的贡献逐渐增大.     

Cross section of electron-nucleus bremsstrahlung near the short-wavelength limit

Using the partial-wave formalism the cross section of bremsstrahlung for a pure Coulomb field is calculated for various atomic numbers of the target nucleus and various incident electron energies. The results are compared to those of previous theories. For intermediate and large atomic numbers the latter cross sections undervalue significantly the present ones. Except for low atomic numbers the cross sections in Born approximation with the Coulomb correction by Elwert yield more accurate results than the cross sections obtained by using the approximate Sommerfeld-Maue wave function. The effect of screening is small for low atomic numbers. At nonrelativistic energies the number of required partial waves is rather large for target nuclei with high atomic numbers, contrary to the expectations. The pertinent results exceed the numerical values including screening by factors of up to five. They verify the assumption that the nonrelativistic cross section of Sommerfeld is fairly accurate even for high atomic numbers.     

Influence of anomalous thresholds in electron-positron annihilation into hadrons: The e+e− → ϱππ cross section

We calculate the cross section for e⁺e^? → ?ππ on the basis of partial-wave dispersion relations in the ππ channel taking proper account of anomalous singularity contributions. The appearance of anomalous thresholds is due to the fact that the vertex γ_V?(ππ) becomes internally unstable as the virtual photon mass is increased. Reasonable agreement with existing data is found. The anomalous singularity contributions provide by far the dominant part of the cross section which is a warning to using naive vector dominance extrapolations in estimating the electron-positron cross section.     

Particle-wave ambiguities in the interpretation of heavy-ion reactions

The relations between the partial wave scattering amplitudes in l-space and the reaction cross section angular distributions are derived in the limits of classical and diffractive scattering. It is shown that a measurement of the angular distribution of a “quasi-elastic” heavy ion reaction does not permit an unambiquous inference of the reaction's partial-wave amplitudes, even for large l. The ambiguities are illustrated with DWBA calculations.     

Determination of partial-wave inelasticities for elastic pion-nucleon scattering with the aid of experimental data on π N → ππ N processes in the beam-momentum range 300 < P beam < 500 MeV/ c

The partial-wave inelasticity parameters of the amplitude for elastic pion-nucleon scattering are determined with the aid of the phenomenological amplitude for inelastic πN → ππN processes in the energy range extending to the threshold for the production of two pions. The resulting inelasticity parameters are compared with their counterparts derived from modern partial-wave analyses. The largest inelastic-scattering cross section in the P11 wave is in excellent agreement with the analogous value from the analysis performed at the George Washington University in 2006. For other waves, however, the present results differ in the majority of cases from respective values given by partial-wave analyses (the distinctions are especially large for the isospin-3/2 amplitudes). Original Russian Text ? V.A. Kozhevnikov, S.G. Sherman, 2008, published in Yadernaya Fizika, 2008, Vol. 71, No. 11, pp. 1891–1909.     

非相干光宽带腔增强吸收光谱技术应用于SO_2弱吸收的测量

非相干光宽带腔增强吸收光谱作为高灵敏检测技术,已成功应用于多种大气痕量气体浓度的测量。根据腔增强吸收光谱技术测量原理可知,若已知测量气体准确浓度,镜片反射率随波长的变化曲线、有效吸收长度、光学腔内有无测量气体吸收前后的光辐射变化,可测量出待测气体的吸收截面。SO_2由于a~3 B_1—X~1 A_1自旋禁阻跃迁,在345~420nm波段吸收截面较低(~10~(-22) cm2/molecule),其测量有一定难度,而准确的弱吸收截面对于卫星反演大气痕量气体浓度以及大气研究等方面均有重要意义。采用365nm LED光源的宽带腔增强吸收光谱实验装置测量357~385nm波段范围SO_2的弱吸收,获得该波段SO_2弱吸收截面,并与已公开发表的SO_2吸收截面进行对比,相关系数r为0.997 3,验证了非相干光宽带腔增强吸收光谱技术准确测量气体弱吸收截面的适用性。     

Elastic collisions of sulfur and hydrogen in their ground states at low temperatures and spectroscopic parameters of SH（X^2∏） radical

This paper constructs the interaction potential of the SH（X^2∏） radical by using the coupled-cluster singlesdoubles-approximate-triples theory combining the correlation-consistent quintuple basis set augmented with the diffuse functions, aug-cc-pV5Z, in the valence range. Employing the potential, it accurately determines the spectroscopic parameters. The present De, Re, ωe, ωeχe, ae and Be values are of 3.7767eV, 0.13424nm, 2699.846 cm^-1, 47.7055 cm^-1, 0.2639cm^-1 and 9.4414 cm^-1, respectively, which are in excellent agreement with those obtained from the measure- ments. A total of 19 vibrational states has been found when J = 0 by solving the radial SchrSdinger equation of nuclear motion. The complete vibrational levels, classical turning points, initial rotation and centrifugal distortion constants when J = 0 are reported for the first time, which are in good accord with the experimental results. The total and various partial-wave cross sections are computed for the elastic collisions of sulfur and hydrogen in their ground states at low temperatures when two atoms approach each other along the SH（X^2∏） potential energy curve. Over the impact energy range from 1.0×10^-11 to 1.0×10^-4 a.u., eight shape resonances have been found in the total elastic cross sections. For each shape resonance, the resonant energy is accurately calculated. Careful investigations have pointed out that these resonances result from the 1 = 0, 1, 2, 3, 4, 6, 7, 8 partial-wave contributions.     

自旋极化电子与Xe原子的弹性碰撞

在电子与无自旋原子的弹性过程中,可认为电子是在一个向心的有效势V(r)中作相对论运动。由Slater定域近似下的相对论自洽场方法(SCF)求得该有效势。在求得有效势的基础上,采用相对论分波法,计算了极化电子与无自旋原子弹性碰撞的散射振幅,进而计算了微分截面和散射电子自旋极化参量。通过与有关的完全实验比较,明确了本文所采用理论方法的适用范围,即在E≥100eV的能量范围内,本文所用理论方法可较好地描述极化电子与无自旋原子的弹性碰撞过程。 关键词：     

Absorption of a massless scalar wave from a Schwarzschild black hole surrounded by quintessence

By using the partial wave method,we investigate the absorption of a massless scalar wave from a Schwarzschild black hole surrounded by quintessence.We obtained the expression of absorption cross section σabs(ω)=π/ω2sum from l=0 to ∞(2l+1)|Tωl(ω)|2=π/ω2sum from l=0 to ∞(2l+1)Γωl(ω).Then we numerically carry out the absorption cross section and we find that the larger the angular momentum quantum number l is,the smaller the corresponding maximum value of the partial absorption cross section is,and that the total absorption cross section tends to the geometric-optical limit σ hf abs ≈πb 2 c.We also find that higher value of ω q(state parameter of quintessence) corresponds to the higher value of absorption cross section σ abs.     

掺镱硼酸盐激光玻璃的光谱性质

测试了掺镱硼酸盐玻璃的吸收光谱和荧光光谱;计算了掺镱硼酸盐玻璃光谱参数;计论了网络修饰体种类、Ｂ２Ｏ３含量和高价离子Ｌａ＾３＋、Ｔｉ＾４＋、Ｎｂ＾５＋、Ｔａ＾５＋氧化物的引入对掺镱硼酸盐玻璃光谱性质的影响,通过两种不同的方法对其受激发射截面进行计算,对结果进行了比较和分析。     

Axisymmetric scattering of scalar waves by spheroids

A phase shift formulation of scattering by oblate and prolate spheroids is presented, in parallel with the partial-wave theory of scattering by spherical obstacles. The crucial step is application of a finite Legendre transform to the Helmholtz equation in spheroidal coordinates. In the long-wavelength limit the spheroidal analog of the spherical scattering length immediately gives the cross section. Analytical results are readily obtained for scattering of Schro?dinger particle waves by impenetrable spheroids, and for scattering of sound waves by acoustically soft spheroidal objects. The method is restricted to scattering by spheroids whose symmetry axis is coincident with the direction of the incident plane wave.     

KN Scattering in 3D Formulation

KN scattering is formulated in three-dimensional (3D) momentum space. A direct product of the relative-momentum state and the spin state is used as the basis state. The spin quantization axis is chosen along the z-axis. The interaction for the KN system is assumed to take the Yukawa-type. It consists of two terms, the central and the spin-orbit one. Calculations for the cross section based on this technique are shown, as well as comparison with the standard partial-wave calculations.     

ns → n′s transition of hydrogen atom by positron impact with screened Coulomb interactions

We have made an investigation on H(ns) → H(n′ s) transition processes by positron impact with screened Coulomb potentials (SCP) by employing a distorted-wave formalism in the momentum space. Making use of simple variational wave functions of the hydrogen atom interacting with SCP we have been able to obtain the partial-wave scattering amplitudes in closed analytical forms. We have then used these distorted-wave scattering amplitudes to make a detailed study on differential and total cross sections in the energy range 20–300 eV. This study reveals some hitherto unknown features of the differential and total cross section. To the best of our knowledge such a study on the differential and total cross sections for inelastic positron-hydrogen collisions with SCP is reported for the first time in the literature.     

Correlation between zeroes and poles ofS matrix for complex potentials

Using several illustrative examples, the nature of resonance poles and the corresponding zeroes of the s-waveS matrix is examined for several potentials having an absorptive pocket followed by a barrier. It is shown that even though the presence of absorption practically suppresses the manifestation of resonance in the elastic scattering cross section, the effect of the resonances generated by the absorptive pocket is more clearly manifested in the absorption cross section provided the barrier width is not too large. We further find that the signature of barrier top resonances are also more clearly manifested in the absorption cross section rather than in the elastic scattering cross section. These results have been interpreted in terms of complex resonance poles and corresponding zeroes of theS matrix. This implies that in complex potential scattering like heavy ion collisions, the reaction channel cross section peak is a more reliable signature of resonance phenomenon than the variation of the elastic channel cross section with energy.     

纳米碳纤维导电性对红外消光性能的影响

纳米碳纤维是一种新型吸波材料。为探讨烟幕粒子的红外消光特性,利用矩量法建立了纳米碳纤维感应电流和散射场的计算模型,在此基础上得出了纳米碳纤维吸收、散射和消光截面的计算表达式。通过Matlab编程计算分析了纳米碳纤维红外消光截面与电导率的关系。结果表明,纳米碳纤维红外消光特性与电导率密切相关,随着电导率的增加,消光截面迅速增加,当波长大于纤维本身长度时,消光截面随电导率的变化出现峰值,峰值电导率与波长有关。     

Forward photoproduction of neutral pions on polarized protons in the third resonance region

Angular distributions of the target symmetry for the reaction γ + p → π⁰ + p have been measured at the Bonn 2.5 GeV Electron Synchrotron at pion c.m. angles between 13° and 63° and photon energies of 1.0 and 1.1 GeV. The π⁰ mesons were detected by their two decay photons with total absorption lead-glass ?erenkov counters. Butanol was used as target material in a continuous flow ³He cryostat operating at 0.5 K and 25 kG. The π⁰ counting rate from free protons in the butanol target was derived from the measurements of the differential cross section on hydrogen. The data are compared with data of other laboratories and the results of two recent partial-wave analyses.     

Absorption of massless scalar wave from Schwarzschild black hole surrounded by quintessence

By using the partial wave method, we investigate the absorption of massless scalar wave from Schwarzschild black hole surrounded by the quintessence. We obtained the expression of absorption cross section
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Then we numerically carry out the absorption cross section and we find that the larger angular momentum quantum number l is, the smaller the corresponding maximum value of partial absorption cross section is, and that the total absorption cross section tends to geometric-optical limit σ_abs^hf≈ π b_c². We also find that higher value of ω_q (state parameter of the quintessence) corresponds the higher value of absorption cross section σ_abs.