Large-angle scattering of heavy ions: (I). General structure of elastic cross section

Closed-form expressions are derived for the differential cross section of elastic heavy-ion scattering at large angles. The derivation is based on the general form of the elastic partial-wave S-matrix in real l-space. By a generalization of analytic techniques developed in earlier work, it is shown that the large-angle scattering cross section has a universal structure involving combinations of Bessel functions and the Fourier transforms of the rapidly varying parts of the S-matrix, irrespective of their dynamical origin. Anomalous large-angle scattering is attributed to deviations of the S-matrix from its “normal strong-absorption profile”, and general conditions for backward-angle enhancement are given. Our model-independent formulation provides the framework for an “inductive” method of analyzing experimental angular distributions and excitation functions aimed at identifying, as uniquely as possible, the dynamical mechanisms that operate in large-angle heavy-ion scattering. Extensions of the formalism to inelastic scattering and transfer reactions, and applications of the analytic method, will be described in subsequent papers.     

Tensor interaction in heavy-ion scattering: (I). The turning-point model

The Heidelberg shape-effect model for heavy-ion tensor interactions is reformulated and generalized using the Hooton-Johnson formulation. The generalized semiclassical model (the turning-point model) predicts that the components of the tensor analysing power $\text{T}{}_{\mathrm{2q}}$ have certain relations with each other for each type of tensor interaction (T_R, T_P and T_L types). The predicted relations between the $\text{T}{}_{\mathrm{2q}}$ are very simple and have a direct connection with the properties of the tensor interaction at the turning point. The model predictions are satisfied in quantum-mechanical calculations for ⁷Li and ²³Na elastic scattering from ⁵⁸Ni in the Fresnel-diffraction energy region. As a consequence of this model, it becomes possible to single out effects from a T_P? or T_L-type tensor interaction in polarized heavy-ion scattering. The presence of a T_P-type tensor interaction is suggested by measured $\text{T}{}_{20}\text{/}\text{T}{}_{22}$ ratios for ⁷Li+⁵⁸Ni scattering. In the turning-point model the three types of tensor operator are not independent, and this is found to be true also in a quantum-mechanical calculation. The model also predicts relations between the components of higher-rank tensor analysing power in the presence of a higher-rank tensor interaction. The rank-3 tensor case is discussed in detail.     

Fast iterative approach to the difference scattering from a dielectric target above a rough surface

1 Introduction Electromagnetic scattering from the target above or beneath a rough surface has at- tracted much interest during recent years, because of extensive applications to radar surveillance, target detection, ground radar probing, and so on[1―3]. In order to numeri- cally simulate scattering from composite model of the target and underlying rough sur- face, some fast numerical methods, such as general forward backward method and spec- trum acceleration algorithm (GFBM/SAA)[4,5], fin…     

Fast iterative approach to the difference scattering from a dielectric target above a rough surface

The difference field RCS (d-RCS) has been defined to analyze the scattering from the target above a rough surface. The electric field integral equations (EFIEs) of the difference induced currentJ _sd on the rough surface, the induced electric currentJ _o and magnetic currentK _o on the dielectric target under a TE wave incidence are derived. A small portion of the rough surface towards the target along the specular direction is taken to compute the scattering contributionE _s0 from the rough surface towards the target, which improves the computation speed. A numerical iterative approach is developed to solve the EFIEs and bistatic d-RCS. The surface length for iterations is dependent on the scattering angle and discussed for comparison with Johnson’s method. Using the Monte-Carlo method to generate the Pierson-Morkowitz (P-M) ocean-like rough surface, bistatic d-RCS of the dielectric target, e.g. a cylinder or a square column, above the rough surface is numerically simulated. The induced electric and magnetic currents on the dielectric target and the difference induced current on the rough surface are numerically discussed.     

KN interactions in the resonance region: (I). Analysis of data

An energy-dependent multichannel K-matrix formalism has been used to analyse two-body $\text{K}\text{N}$ data n the region E_CM ? 2 GeV. Details of the data analysis are presented.     

斜程大气湍流中漫射目标的散射特性

根据推广的惠更斯-菲涅尔原理及ITU-R大气结构常数模型(2001年国际电信联盟提出的随高度变化的大气结构常数模型),考虑了大气湍流对激光从发射机到目标和从目标到接收机双程路径的影响,研究了大气湍流中漫射目标的激光波束散射问题,导出了考虑对数振幅起伏和相位占优情况下在斜程大气湍流中传输时激光波束散射场的互相关函数、强度协方差和强度方差的计算公式,并给出了数值计算结果.数值分析了波长、接收机高度和传播距离对强度协方差和归一化强度方差的影响. 关键词： 激光散射 斜程湍流 强度方差 强度协方差     

Phenomenology of asymptotically free theories in deep inelastic scattering: (I). Electron and muon scattering

We calculate the predictions of asymptotically free theories for deep inelasric scattering using a straightforward Mellin transform technique which uses a minimum of theoretical assumptions. Parameterizing the quark and anti-quark distributions functions, we fit all the available μ and e scattering data. We investigate the sensitivity of the theory of the (almost) unknown gluon distributions and the choice of scaling variable. The best fit uses the formalism of Georgi and Politzer for the 1/Q² terms with a quark gluon coupling constant g²/4π ～ 1 at Q² = 1 (GeV/c)². (Equivalently the scale parameter Λ is 500 MeV/c.) Good fits are also found in simpler models using x, x′ or ξ as scaling variables. The best value of Λ depends strongly on the choice of scaling variable.     

Dispersion relations and low-energy elastic scattering of charged particles from nuclei: (I). Theory

Dispersion relations for the elastic scattering of charged particles from nuclei are deduced for the case of potential scattering. The inclusion of the Coulomb interaction leads to a simple modification of the formalism developed so far for uncharged projectiles only.     

Beta-delayed proton emission from heavy nuclei: (I). The observation of coincidences between protons and γ-rays

Coincidences have been detected between γ-rays and β-delayed protons emitted after the decay of very neutron-deficient nuclei. In the three cases studied the decay proceeds to the ground state with branches to the first excited (2⁺) state of the even daughter nucleus of (58±7) % (¹¹⁵Xe to 709 keV in ¹¹⁴Te), (14±3) % (¹¹⁷Xe to 679 keV in ¹¹⁶Te), and (50±10) % (¹⁸¹Hg to 158 keV in ¹⁸⁰Pt). Upper limits of 2 and 6 % can be placed on the branches to the 4⁺ states of ¹¹⁴Te and ¹⁸⁰Pt. For the cases of ^115,117Xe, coincidences with annihilation radiation were also observed; the measured positon/proton ratio determines the difference Q—B_p, between the energy available for electron capture and the proton separation energy for the daughter. For ¹¹⁵Xe the result is 6.20±0.13 MeV, for ¹¹⁷Xe 4.10±0.20 MeV.     

Multiple-reflection effects in hadron-nucleus scattering: (I). Cluster expansion of the optical potential

A basic assumption underlying the high-energy hadron-nucleus optical potential is that no target nucleon is struck more than once. Although this condition is satisfied at high energy, such is not the case in the vicinity of medium-energy resonances, where the amplitude for the projectile to undergo multiple reflections between two target nucleons is quite large. As a remedy for this problem, the multiple-scattering series is rearranged such that the optical potential can be expressed as a cluster expansion. The lowest order optical potential is modified by a two-body cluster term, which is a sum of all possible reflections of the projectile between a pair of target nucleons. This term is evaluated for a model potential within the formalism of Foldy and Walecka: it is substantially smaller than the contribution of a single reflection, and its overall effect is small under certain additional restrictions. If the independent-pair picture of nuclei is valid, then the three-body cluster term may be small, and the lowest order Glauber optical potential can provide a self-consistent picture of hadron-nucleus interactions, even though a term-by-term expansion of the multiple-scattering series does not provide such assurance.     

Hadron scattering in two-dimensional QCD: (I). Formalism and leading order calculations

Two-dimensional quantum chromodynamics in the 1/N_c expansion is explored as a model for hadronic interactions. In meson-meson scattering, order 1/N_c terms exhibit embryonic “Regge” behaviour, with the crossed channel factorization, signature and exchange degeneracy properties found in dual Regge models. “Regge” intercepts are additive in the quark quantum numbers exchanged, and have a lower limit for large quark masses. Residues also factorize in the direct channel. An analogue for fixed angle scattering is presented which has deviations from dimensional counting rules related to form factors and Regge intercepts.     

Electron-nucleon interaction in quasi-free scattering: (I). Non-relativistic Hamiltonian through second order

In the frame of a program aiming at examining the approximations involved in the theoretical treatment of (e, e′p) reactions, the electron-nucleon interaction producing the knock-out mechanism is considered in the non-relativistic approach of McVoy and Van Hove and compared with the relativistic one based on the one-photon-exchange Feynman graph. In this paper the non-relativistic Hamiltonian through second order in the nucleon recoil velocity is adopted; in the next paper higher order terms are included. The two approaches appear equivalent as far as the usual DWIA cross section is concerned, where a factorization occurs between the electron-nucleon cross section and the nucleon momentum distribution. However the unfactorized DWIA cross section behaves differently. This is attributed to a different off-shell behaviour of the two scattering amplitudes.     

Potential of multiphoton exchange in the scattering of light charged particles of a heavy target

Classical solution of the inverse problem of determing the potential for differential scattering cross section was obtained by O.B. Firsov in 1953. We use it to investigate the deviation from the Coulomb potential due to the exchange of two or more photons in the scattering of an electron in an external field produced by a heavy nucleus with charge Z _e . We also construct the effective potential acting on a charged particle in the problem of planar channeling.     

Elastic and inelastic scattering of neutrons from Fe and Cu : (II). Scattering and nuclear structure effects from coupled channels calculations

The differential cross sections for neutron scattering from ^{54, 56}Fe and ^{63, 65}Cu at energies between 8 and 14 MeV, which were reported in a companion paper, have been analyzed in the framework of the coupled channels formalism. Neutron potential deformations were extracted and compared with corresponding deformations deduced from the reanalysis of proton scattering measurements and Coulomb excitation results. The size of the Coulomb correction term in the absorptive proton potential is discussed. Matter root-mean-square radii are estimated from our potential and compared with results from -particle folding model calculations.     

Generalized fresnel model for very heavy ion scattering: (II). Relation to the optical model

The generalized Fresnel model presented in part I as a simplified method for analyzing angular distributions of very heavy ion scattering is used here with an alternative parameterization of the partial-wave S-matrix. Its form is suggested by analytic expressions for the reflection function and nuclear phase shifts derived by Kauffmann from conventional optical potentials. This enables us to formulate explicitly the relationships between the l-space and r-space properties of the elastic heavy ion interaction, in particular the continuous ambiguities and other features found empirically from optical model calculations.     

Polarization of recoil protons from proton Compton scattering in the region of the second πN resonance

The polarization of recoil protons from proton Compton scattering has been measured at an angle of 90° c.m.s. in the region of the second nucleon resonance. The scattered photons were detected by a telescope which consisted of a lead plate converter, scintillation-counter hodoscopes and a ?erenkov counter, The angles and momenta of recoil protons were analyzed by a magnet with four spark chambers. The polarization of protons was obtained from the asymmetry in the elastic scattering of protons on carbon in a spark chamber.     

The scattering of ions from a clean solid surface in the 1 to 10 eV range

We have proposed a surface model which consists of partially screened spherical caps oscillating in a direction normal to the undisturbed surface to correlate measurements of the trapping probability of sodium and potassium ions on clean (110) tungsten surfaces at energies of 1 to 15 eV and incidence of 10° to 70° from the normal to the surface. The trapping probability may be represented as a relatively simple function of angle, mass ratio, surface temperature and beam energy to ionization potential ratio, with good agreement with experimental data. The model depends on some assumptions about elevation and azimuthal screening of lattice sites which cannot fully be justified from first principles. Further analysis of the data, particularly with respect to scattered particle distribution and additional data for the scattering of lithium and cesium might help refine those assumptions.     

Measurement of the average neutrons yield from 250 MeV protons absorbed in a lead target

Neutron yield from 250 MeV protons accelerated by the ITEPh synchrotron was measured in a lead target 5 cm diameter and 10 cm long. The observed total yield is 2.56±0.27 neutrons/proton, where the evaporation and cascade components are 2.30±0.25 and 0.26±0.11 neutrons/proton respectively.