Effects of E2 and El-E2 Interference on Coulomb Dissociation of 19C

We investigate the effects of higher order multipole transitions, in particular electric quadrupole （E2） and El-E2 interference, on the Coulomb dissociation of 19 C within the framework of the first order eikonal approximation. The sensitivity of the total Coulomb breakup cross section and the longitudinal momentum distribution of the core fragment to these effects are checked. The breakup occurs predominately through the dipole transition and the contribution of E2 transition to the total cross section is found to be within the range from 1 to 3% of that of El. It is further observed that the El-E2 interference term contributes nothing to the integrated cross section. On the other hand, the longitudinal momentum distribution is observed to be insensitive to the E2 transition while the El-E2 interference introduces a small asymmetry in its shape.     

A comment on the electric dipole sum rule for nuclear photoeffect

Gerasimov's argument on the E1 sum rule for nuclear photoeffect is shown not to hold exactly in simple non-relativistic models. The retardation effect does not precisely cancel the contribution of higher multipoles and remaining terms have about the same magnitude as the cancelled ones. They are also found to be of the order of relativistic correction so that the consistent argument on the higher multipole and retardation effects seems to require a relativistic treatment.     

Electromagnetic processes in relativistic heavy ion collisions

Electromagnetic effects in relativistic heavy ion collisions with impact parameter larger than the sum of the nuclear radii are studied using the virtual photon method. With increasing value of the relativistic parameter γ the hardness of the virtual photon spectrum increases. This leads to interesting new effects which will also have to be considered in the design of future relativistic heavy ion machines and experiments. The excitation of high-lying giant E1 and E2 multipole resonances is calculated as well as electromagnetic pion production. Coulomb bremsstrahlung is calculated and compared to the bremsstrahlung emitted in the more violent central nuclear collisions. K-shell ionization and electron-positron pair production is studied. The latter process has a very large cross section for heavy ions and contributes significantly to the stopping power of relativistic heavy ions in a dense medium.     

Out of plane measurements of the decay neutron from the giant resonance in the 12C(e,e(')n)11C reaction

Out of plane measurements of the angular correlations for the 12C(e, e(')n) reaction have been performed for the first time in the giant resonance region. The cross sections were directly separated into the longitudinal and transverse, longitudinal-transverse, and transverse-transverse components. The cross section at the peak of the giant resonance ( omega = 22.5 MeV) has been found to be almost all longitudinal. It was reproduced by the multipole expansion with E0 and E2 components besides E1. The longitudinal-transverse component might have a maximum around 24 MeV. The transverse-transverse component is very small over the giant resonance.     

Photodisintegration of He

Total and differential cross sections for the reaction ³He(γ, d)¹H have been measured from 13 MeV to 45 MeV using a magnetic spectrometer and solid-state detectors. The results agree well with some of the previous measurements. A systematic study of the energy and the angular dependence of the cross sections shows that the E2 cross section increases with increasing energy indicating relative importance of the higher-order multipole transitions in the disintegration process. The isotropic terms in the angular distribution also increase with energy, suggesting the importance of D-state in the ground state of ³He. Comparison of our experimental data with the available theoretical calculations is also presented.     

Neutron elastic and inelastic scattering from 28Si, 32S and 34S

Differential cross sections for the elastic and inelastic scattering of neutrons from the sd-shell nuclei ²⁸Si, ³²S and ³⁴S have been measured in the 20–26 MeV region. The data are analyzed in terms of the rotation-vibration (²⁸Si) and anharmonic vibration (^{32, 34}S) collective models. Isoscalar E2, E3 and E4 transition matrix elements are obtained from the normalized multipole moments of the real potential and the results are compared with those obtained from electromagnetic probes and from nuclear structure theoretical calculations.     

Convergence of the multipole results for first order orientation dependent intermolecular forces using NH3-H+ as a model interaction

The NH₃-H⁺ interaction is used as a model for discussing the usefulness of energy multipole expansions for interactions where the first order energy plays an important role. The multipole results for the first order energy are analysed formally and are compared numerically with the non-expanded first order energy for a variety of NH₃-H⁺ relative configurations. The results are used to discuss the limitations of the multipole expansion of the first order energy which can be very severe for some NH₃-H⁺ collision trajectories.     

Weak neutral-current effects in electron-scattering coincidence experiments

Using a recently developed helicity analysis of electron-scattering coincidence experiments, we derive general expressions for the asymmetry in the coincidence cross section with polarized incident electrons. The asymmetry cross section is expressed in terms of the helicity components of the electromagnetic and weak neutral currents in the center-of-momentum frame. The asymmetry arises from an interference between the electromagnetic and weak neutral currents and from parity admixtures in the nuclear wave functions. In the limit of heavy, static nuclei, connection can be made to the usual multipole matrix elements of the electromagnetic and weak interactions. Some simple examples are discussed for the case where the reaction proceeds through a single intermediate resonance.     

Second-order orientation effects in light scattering by polarized atoms

A compact expression is derived for the part of the cross section for light scattering by axisymmetrically polarized atomic systems proportional to the third-rank state multipole. The effect of the second-order orientation determined by this state multipole on the polarization and angular distribution of the scattered light is studied. The polarization of the incident light can be arbitrary and is specified by the Stokes parameters. A number of orientation effects in the scattering process are shown to be induced precisely by the second-order orientation. In particular, when nonpolarized light is scattered by an oriented atom, the scattering intensity in the perpendicular direction depends on the second-order orientation alone. The second-order orientation also preserves circular dichroism in the linear polarization of the forward-and back-scattered light.     

Neutral-current neutrino–nucleus cross sections for A∼50–65 nuclei

We study neutral-current neutrino–nucleus reaction cross sections for Mn, Fe, Co and Ni isotopes. An earlier study for a few selected nuclei has shown that in the supernova environment the cross sections are increased for low energy neutrinos due to finite-temperature effects. Our work supports this finding for a much larger set of nuclei. Furthermore we extend previous work to higher neutrino energies considering allowed and forbidden multipole contributions to the cross sections. The allowed contributions are derived from large-scale shell model calculations of the Gamow–Teller strength, while the other multipole contributions are calculated within the random phase approximation. We present the cross sections as functions of initial and final neutrino energies and for a range of supernova-relevant temperatures. These cross sections will allow improved estimates of inelastic neutrino reactions on nuclei in supernova simulations.     

Manifestation of the second-order alignment in light scattering by polarized atoms

An expression for the cross section of light scattering by axisymmetrically aligned atomic systems is derived in a compact form. The cross section under consideration is proportional to the state multipole of the fourth rank. The effect of the second-order alignment determined by the fourth-rank state multipole on the polarization and the angular distribution of scattered light is investigated. The polarization of incident light can be arbitrary and, in the general case, is specified by the Stokes parameters. In particular, it is demonstrated that the second-order alignment cannot induce circular polarization of scattered light and does not influence the dissipation-induced effects of circular dichroism associated with the first-order alignment but leads to a change in the angular distribution and the degree of linear polarization of the scattered light.     

Scalar and Pseudo-Scalar Form Factors in Electro- and Weak-Production of Pion Near Threshold

We investigated pion production near threshold by the weak current in terms of multipole amplitudes. By exploiting the chiral Ward identity based on the QCD Lagrangian, we derived relevant multipole amplitudes in closed forms and presented their numerical results. In the amplitudes, scalar and pseudo scalar (PS) form factors, which represent the scalar and the PS quark density distributions, manifest by themselves. We applied these amplitudes to the cross sections for the weak- and electro-production near threshold. Both pion and PS form factor contributions are shown to account for the t-channel contribution in the charged pion electro-production near threshold. The asymmetry on the pion production by the neutrino and anti-neutrino is also discussed with their longitudinal and transverse cross sections.     

Calculation of Interaction Potentials between Spherical and Deformed Nuclei

The interaction potential for spherical-deformed reaction partners is calculated. The shape, separation and orientation dependence of the interaction potential and fusion cross section of the system ^32S＋^154Sm are investigated within the double-folding model of the deformed nuclei. The effective nucleon-nucleon interaction is taken to be the M3Y-Reid potential. The density is considered for three terms of the expansion using the truncated multipole expansion method, which is a deformed Fermi shape With quadrupole and hexadecapole for the density distribution of ^154Sm. It is found for the interaction potential that the height and the position of barrier strongly depend on the deformations, the orientation angle of the deformed nucleus, and hence produce great effects on fusion cross section. The integrated fusion cross section is in good agreement with the experimental data.     

On the coupling of the giant multipole resonances to the surface quadrupole oscillations of nuclei

Within the framework of the hydrodynamic model the exact coupling constants of the coupling of the giant multipole resonances to the surface quadrupole oscillations of nuclei are derived. The differences to former variational calculations are discussed. It is found that the coupling constants for the terms linear in the surface variables are almost the same whereas the coupling constants for the quadratic terms differ appreciably. The influence on the photon absorption and scattering cross sections of spherical nuclei is discussed.     

Analysis of E1 and E2 radiative α-capture and giant multipole resonances

Experimental data on E1 and E2 radiative α-capture are analyzed by taking account of direct and semidirect processes as well as the compound process. Observed excitation functions for these reactions are reasonably well reproduced assuming the reactions take place mainly through giant multipole resonances. It is shown that the compound process dominates in the lower energy region especially for E1 capture whereas in the higher energy region direct and semidirect captures are the major processes especially for E2 capture. Several interesting results are obtained on α-particle spectroscopic factors of target ground states and on spreading widths and isospin-mixing coefficients of the giant multipole resonance states. The data are shown to be consistent with the existence of the isoscalar giant quadrupole resonances. The applicability of direct and semidirect capture theories to α-capture is examined.     

Cardiac magnetic source imaging based on current multipole model

It is widely accepted that the heart current source can be reduced into a current multipole. By adopting three linear inverse methods, the cardiac magnetic imaging is achieved in this article based on the current multipole model expanded to the first order terms. This magnetic imaging is realized in a reconstruction plane in the centre of human heart, where the current dipole array is employed to represent realistic cardiac current distribution. The current multipole as testing source generates magnetic fields in the measuring plane, serving as inputs of cardiac magnetic inverse problem. In the heart-torso model constructed by boundary element method, the current multipole magnetic field distribution is compared with that in the homogeneous infinite space, and also with the single current dipole magnetic field distribution. Then the minimum-norm least-squares (MNLS) method, the optimal weighted pseudoinverse method (OWPIM), and the optimal constrained linear inverse method (OCLIM) are selected as the algorithms for inverse computation based on current multipole model innovatively, and the imaging effects of these three inverse methods are compared. Besides, two reconstructing parameters, residual and mean residual, are also discussed, and their trends under MNLS, OWPIM and OCLIM each as a function of SNR are obtained and compared.     

Trajectories of Charged Particles in Radial Electric and Uniform Axial Magnetic Fields

The trajectories of charged particles were determined over a wide range of parameters characterizing the motion in cylindrical low-pressure gaseous discharges and plasma-heating devices which have steady radial electric fields E perpendicular to uniform steady magnetic flelds B. Three radial distributions of E were considered: E ? r, constant E, and E ? r-1. These distributions are characteristic of the fields measured in a modified Penning discharge, in two NASA Lewis Bum-out-type plasma-heating devices, and that estimated for the Ixion device, respectively. The plasmas of such ? × B? devices are often characterized by their high ratios of drift energy to mean particle energy, finite gyroradius effects, and sizeable electric field changes in the distance covered by a cyclotron radius. Such particle motions are not amenable to simple guiding center theory. From numerical calculations of the actual trajectories it was concluded that the differences between cyclotron frequency and qB/m, and between azimuthal drift and a guiding center approximation (including ? × B? and centrifugal force terms) are appreciable. The net cyclotron motion obtained by subtracting the actual drift from the trajectories, however, has a nearly circular contour over which the speed is quite constant.     

基于微观IBM对电子-核散射及核电磁性质的研究(I) BE理论方案

从价核子自由度出发构造出核跃迁电荷/电流密度算符,采用Dyson玻色子展开技术给出了获取核玻色子形式跃迁电荷/电流密度有效算符的一种微观方法(BE方法).利用微观相互作用玻色子模型(IBM)提供的波函数可在玻色子态空间中求出核跃迁电荷/电流密度,结合电子-核散射以及核电磁跃迁的形式理论,建立了可研究电子-核散射各种形状因子,微分散射截面以及核约化跃迁几率、电磁多极矩、核态g因子等物理量的理论方案.在一种微观sdIBM-2框架下,结合现有理论方案,初步计算了