Alignment effects in deuteron total cross sections

The alignment dependence of the total cross section of deuterium is a purely multiple scattering phenomenon. An estimate of this for pion scattering using Glauber theory shows that the most important contribution is associated with the deuteron D-state (typically 1%) with corrections coming from the double spin flip. Measurements of the proton total cross section with an aligned deuteron beam should also yield other interesting information on the wave function of the deuteron D-state.     

The singlet deuteron and trinucleon-induced stripping reactions

The normalization factor for zero-range and finite-range DWBA calculations of (h, kd) reactions has been determined by three theoretical methods. Although the values obtained show a fair spread, they are all, nevertheless, close to the single N(h, kd) extracted from experiment.     

Effects of nuclear deformation on neutron total cross sections

Neutron total cross section differences have been determined for ^150,152,154Sm from 0.8 to 15 MeV by measuring transmission ratios. Significant differences were observed for ^152,150Sm and for ^154,150Sm. Evidence is presented that these results can be attributed to nuclear deformation.     

Angular and energy dependences of cross sections for deuteron electrodisintegration at subbarrier energies

A method is proposed for analyzing a large set of spectra calculated for the Coulomb breakup of deuterons. The regularities in the behavior of the respective cross section as a function of the emission angles and energies of particles constituting the deuteron are studied on the basis of this method. The deuteron-breakup reaction on lead nuclei at an energy of E _d = 8 MeV is considered by way of example. It is shown that the approximate Landau-Lifshitz formulas for this process are unable to predict some of its features. An experiment is proposed for studying the physical nature of the Nemets effect.     

Relations between the differential cross sections for diffractive processes of nucleon stripping and halo-nucleus core stripping

A comparative analysis of the nucleon stripping and core stripping reactions induced by a halo nucleus is presented on the basis of certain models for diffractive processes. It follows from calculations for the halo nucleus 11Be that the transverse momentum distribution of nucleons for core stripping (as the longitudinal momentum distribution) is less distorted by absorption in a target than the distribution of core fragments for nucleon stripping. The obtained relations between the cross sections for the stripping reactions simplify interpretation of the calculation results.     

Electronic relativistic effect on the ratios of deuteron to alpha-particle induced K-shell ionization cross sections

The ratios of the K-shell ionization cross sections induced by deuterons to those induced by α-particles with the same velocities have been calculated in the plane wave Born approximation using relativistic hydrogenic wave functions for the target electrons. The numerical results are compared with the recent experimental valus of Chang et al. The use of relativistic wave functios considerably improves the agreement with the experimental data.     

Three-body model of deuteron breakup and stripping

For a three-body model Hamiltonian, the scattering eigenfunction that corresponds to an incident deuteron is expanded in terms of eigenfunctions of the neutron-proton relative Hamiltonian, as suggested by Johnson and Soper. In this expansion, breakup is represented by an integral over the continuum of neutron-proton scattering states. Only states of zero relative angular momentum are included; the validity and advantages of this approximation are discussed. The continuum is divided into five discrete channels, whose coupling to each other and to the deuteron channel is treated by solving coupled differential equations with appropriate boundary conditions. It is found necessary to use a simple WKB method to take account of the long-range coupling among breakup channels; this method introduces potential matrices W and S that describe local and derivative coupling of the channels. The reaction of breakup on the elastic channel is neglected.The properties of W and S and the breakup wavefunction are examined for the case of 22.9 MeV deuterons incident on a target of mass number A ≈ 40. The Coulomb interaction is ignored, and a local Gaussian shape is used for both the real and imaginary parts of the nucleon-nucleus optical potential.It is found that a rather broad spectrum of n-p continuum states is excited, especially for low center-of-mass angular momentum. This result weakens the justification for the Johnson-Soper adiabatic theory, which emphasizes breakup into states of low relative energy.The breakup part of the wavefunction at zero n-p separation is comparable with the elastic part, but is important only over a surprisingly short range in the center-of-mass coordinate, with the result that breakup cross sections are quite small. Nevertheless, breakup produces major modifications of (d, p) cross sections. These modifications can to some extent be simulated by the Johnson-Soper method. The breakup wavefunctions show several interesting effects in their dependence on angular momentum and radius.     

The break-up of the deuteron and stripping to unbound states

We treat the break-up of the deuteron in the field of a heavy nucleaus. Our theory is based on the post formalism of the DWBA, which is discussed in detail. In particular we consider the case where the energy of the incoming deuteron is below the Coulomb barrier. This sub-Coulomb break-up permits a test of the DWBA by comparing experimental data with the theory. Small effects are investigated in this context, and other treatments of this process are reviewed critically. To give an intuitive picture of the break-up process we introduce a semiclassical model.In the second part the theory is extended to stripping reactions to unbound (resonant) states. We show that this reaction which interferes with the direct break-up process, can again be well described in the post-form of the DWBA. Using simple models we discuss the most important features of such reactions. Particular attention is paid to the “l-enhancement”, “parallelism” and the influence of the specific wave functions on resonance line shapes. A survey and comparison of various theories of stripping reactions to unbound states is given and finally we discuss possible future developments.     

An approximate three-body theory of deuteron stripping

A treatment of deuteron stripping is developed in which the three-body effects associated with deuteron break-up in the nuclear field are included explicitly. The essence of the method is the choice of a convenient discrete set of n-p eigenfunctions as a representation of the three-body continuum effects. This approach leads to a distorted wave stripping matrix element similar to that of the DWBA, except that the elastic deuteron wave is replaced by a three-body wave function given as the solution of a set of coupled two-body Schrödinger equations. The adiabatic theory of Johnson and Soper appears as the solution in a suitable first approximation. This new formalism should prove useful in the evaluation of corrections to three-body models of the deuteron-nucleus system, in particular those models in which the nucleon-target interaction is represented by a complex local optical potential.     

Theory of deuteron stripping on doubly even nuclei

Using the method of quantum Green functions we derive a rigorous formula for the deuteron stripping on a doubly even nucleus. Starting from this formula we discuss the distorted-wave Born approximation, some additional assumptions usually made in numerical calculations and the high-energy case. In addition to this we show that the formfactor can be calculated using a model for the nucleon self energy.     

Partial cross sections in a plasma

The collision integral for a plasma obtained in the ring approximation with a preliminary ladder renormalization is used to determine the first two partial cross sections. Numerical calculations show that the partial cross sections display a very nonlinear behavior (in logarithmic scale) and do not diverge at small values of the plasma parameter.     

On the calculation of scattering cross sections from absorption cross sections

A dispersion-type relation between photon scattering and absorption cross sections is derived. It is shown that the relation gives the correct scattering cross section in the low and high frequency limits, and is consistent with the Kramers-Heisenberg formula in the vicinity of a resonance. The practical application of the relation is illustrated by calculations of the scattering cross section and refractive index of He and Ne at STP and dry air at 1200°K from known absorption cross section data. The method is useful for obtaining scattering cross sections, polarizabilities, and refractive indices at elevated temperatures.     

The rise of total cross sections and a critical pomeron

The framework of a Reggeon Field Theory with thresholds in rapidity is used to predict the rise of pp total cross section while maintaining the critical character of the pomeron.     

Excitation cross sections for a vanadium atom

Moscow Power Engineering Institute, 14 Krasnokazarmennaya Str., Moscow, 105835, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 6, pp. 16–21, November–December, 1995.     

Radar cross sections of a random medium layer

Analytic expressions are derived for the normalized radar cross sections (NRCS) of a random medium layer. These are calculated from the first-order solutions for diffuse intensities which are based on a multiple-scattering wave theoretical analysis. The permittivity fluctuations are assumed to be small and to obey stationary Gaussian statistics. On studying the expressions for the NRCS, some of their characteristics are pointed out. Three different correlation functions are considered and expressions for the coherent propagation constants are provided. Numerical examples are used to verify theoretical results and highlight some interesting characteristics of NRCS.     

Radar cross sections of a random medium layer

Abstract

Analytic expressions are derived for the normalized radar cross sections (NRCS) of a random medium layer. These are calculated from the first-order solutions for diffuse intensities which are based on a multiple-scattering wave theoretical analysis. The permittivity fluctuations are assumed to be small and to obey stationary Gaussian statistics. On studying the expressions for the NRCS, some of their characteristics are pointed out. Three different correlation functions are considered and expressions for the coherent propagation constants are provided. Numerical examples are used to verify theoretical results and highlight some interesting characteristics of NRCS.     

The fast computation of the compound cross sections

A method is formulated and studied which allows to quickly calculate the fluctuation component of the average cross section for different absorption values in the channels and in the presence of direct inelastic transitions. The experimental data on neutron scattering by^182,184,186W are analyzed.