Table of contents

The scope and importance of ion bombardment studies has in recent years been considerably extended by the realization that the surface properties of materials, and in particular the semiconductors, may be usefully modified by means of the implantation of suitable ions in the form of an accelerated beam. Whereas earlier studies of radiation damage and sputtering were confined mostly to low ion energies, interest has now grown in the behaviour at higher energies, up to the Mev region. Often the bombarded specimens are crystalline, and the so-called channelling phenomenon is important in determining the range distribution of implanted material and the degree of lattice disruption created.

After a summary of the various commonly used approximations to the interatomic potential, the energy loss mechanisms of ions in solids are discussed and experimental results are compared with theoretical predictions for both the amorphous and crystalline cases. In the next section, attention is focused upon the radiation damage produced by ion bombardment of crystalline targets, and the migration and clustering of radiation-induced defects is discussed.

The sputtering process is described and recent work is summarized. In this, and the following section on secondary electron emission, the behaviour of single-crystal targets has proved important in understanding the physical nature of the process. Modern developments in ultra-high vacuum technology have aided both these studies.

A lengthy account is given, in the final section, of the physical processes involved in ion implantation. The advantages of this method of doping semiconductor crystals are discussed, as well as some attendant problems. Examples of the practical application which has already been made are given, and the equipment required for such work is described. A certain degree of speculation is hazarded regarding the future prospects of the ion-implantation technique in research and industrial applications.

We review recent developments in the theory of Green functions (off-shell S-matrix elements) and their applications in elementary particle physics (particularly strong interactions). We concentrate on dynamical problems, taking the underlying particle symmetries for granted. Green functions were first considered as an offshoot of quantum field theory as applied in quantum electrodynamics, and our introduction sketches how this historical background has affected the development of both on-shell and off-shell methods for the strong interactions. Most of the detailed applications of Green function methods are in two-body elastic scattering at moderate relativistic energies (neglecting production processes). The main tool here is the Bethe-Salpeter equation in the ladder approximation. We derive the Bethe-Salpeter equation by summing Feynman graphs, and give a critical review of its application to various scattering and bound-state problems (nucleon-nucleon, pion-nucleon and pion-pion systems), including where available detailed comparisons with the results of dispersive and potential-theoretic calculations. We review very briefly the use of the Bethe-Salpeter equation as a `model' for the Regge-pole hypothesis and the quark hypothesis. We then go on to consider processes involving more than two particles, and the `internal' multiparticle (or many-body) structure of the corresponding Green functions. This structure can be simply and plausibly expressed by a set of generalized Bethe-Salpeter equations which together represent an off-shell version of unitarity. We rederive the graphical restrictions previously imposed on the kernles of two-body Bethe-Salpeter equations, and we derive the relativistic Faddeev-type three-body linear equations.

During the last decade, considerable progress has been made both experimentally, in determining to high precision the hadron-nucleon total cross sections, and theoretically, in accounting for the magnitude and behaviour of these cross sections as a function of energy. The work is chiefly concerned with those hadrons (pions, kaons, nucleons) normally obtained in particle beams at proton synchrotrons, and the basis of the experimental method, involving electronic counter techniques, is discussed in some detail. The experimental data have revealed a wealth of information on the energy dependence of the hadron-nucleon interactions.

While the review has been written from an experimentalist's point of view, a discussion of some of the pertinent theoretical aspects is included.

This article reviews briefly the phenomenological work done on production processes in the year 1967-8. The unusual activity in this subject during that period was due to the emergence of first, a large amount of good-quality new bubble chamber data, and second, practical forms of the multi-Regge model. The result is a consistent, though crude picture of inelastic collisions in general. This resultant picture is presented here with ample illustrations from existing data, but with no attempt at completeness. Later developments are also briefly indicated.

In a brief introductory section the derivation of the Shubnikov groups and their importance in the description of the symmetries of magnetic crystals is described. The derivation of the black and white Bravais lattices and of the Shubnikov point groups and space groups is described and there is a brief discussion of spin space groups. In a later section the determination of the corepresentations of these non-unitary groups is discussed.

The remainder of the article is devoted to a description of the various uses which can be made of the magnetic groups and of their corepresentations in studying various properties of magnetic crystals. These applications include: the simplification of the form of a tensor describing either some macroscopic static property or some transport property or some microscopic property of the crystal; the determination of the shape of the Brillouin zone of a magnetically ordered crystal; Landau's theory of second-order phase transitions; spontaneous currents and superconductivity; crystal field theory; space-group selection rules; the symmetry properties and degeneracies of magnons and paramagnons in magnetic or nearly-magnetic crystals; the symmetry properties and degeneracies of the electronic band structure of a ferromagnetic metal. In conclusion there is a brief discussion of the polychromatic groups.

An examination is made of the current problems of the communication and dissemination of literature in the field of physics. The growth of the literature is considered quantitatively with respect to the form, subject and origin of published material. This is related to the general growth in scientific activity as exemplified by increases in numbers of physicists and of expenditure on research. The results of surveys aimed at ascertaining the needs or demands of users of the physics literature are considered, particularly where these reveal weakness in the present organization of information transfer, and the reactions of users to new services intended to remedy the deficiencies. Finally, a number of recently established services - some designed to meet hitherto unsatisfied needs - are described. The role of the computer in the development of local, national and international documentation systems is examined.