Positron Physics , M. Charlton and J. W. Humberston Cambridge U. Press, New York, 2001. $120.00 (454 pp.). ISBN 0-521-41550-0
Positron Physics by Michael Charlton and John W. Humberston is a clearly written compendium of theories and experiments on the elastic and inelastic scattering and annihilation of individual low-energy positrons and positronium atoms interacting with gas molecules. About three-quarters of the text is devoted to this material, to which the authors have made many original contributions. The book contains, as well, an introduction to positron experimental techniques and material covering the atomic properties of positronium and other small bound systems containing positrons. The book’s completeness on its principal topics, including references to about 800 of the original works, is exhaustive enough that I shall finally be able to discard my extensive reprint collection.
While there are many review articles and countless edited volumes summarizing progress in positron solid-state physics, positron atomic physics and positron astrophysics, Positron Physics is a real textbook, though without exercises. Its unifying viewpoint and beautiful format as a Cambridge University Press monograph should be an inspiration for others similarly to summarize some other aspects of the last half-century of positron work in textbook format.
Such future writers will now have a high standard to meet, a standard that avoids obfuscation and includes distillation to obtain the essence of results by many workers. The interactions of positrons with atoms and molecules are simply categorized (static, polarization, exchange, positronium formation, and annihilation) and the Born series and the optical theorem are introduced in the second chapter. The authors offer very clear explanations. They point out, for example, that the total scattering cross sections for electrons and positrons are already nearly identical at energies that are not high enough to be dominated by the first term in the Born approximation. This phenomenon is explained as being due to the smallness of odd terms in the Born series if exchange and energy differences between atomic states can be neglected. Another example of the simplification of otherwise unintelligible theory is a geometrical argument showing why positronium formation following positron impact at high energies must be described by the second Born approximation. Similar geometrical pictures help the uninitiated to appreciate the difficulty encountered in treating positron impact ionization near threshold, where the outgoing electron and positron are likely to have correlated motion that cannot be distinguished from a weakly bound state of positronium.
Those readers who retain no reprint reliquaries will find invaluable the many figures summarizing all the available data and theories, minus the ones shown to be flawed in careful and courteous discussions of systematic errors. Some of the figures, like the one (2.10) exhibiting the positron–neon total scattering cross section from seven experiments and three theories, are decades old; nevertheless, upon seeing the amazingly low cross section (0.1 πa 0 2) at 0.6 eV (the famous Ramsauer minimum), I still cannot help dreaming about positrons that find themselves captured for a long time at low energies. Equally valuable to positron schemers are the compendia of recent measurements, examples being the cross sections for positron impact ionization of atomic H and a list of positron mobilities in various molecular gases.
The last part of the book contains an introduction to positronium and exotic, positron-containing species, that will serve to point the reader to a number of other fields based on the world’s most easily obtained antiparticle. Having found only one tiny mistake in my perusal of the book (figure 1.6 appears to display an incorrect momentum vector summation), and being both sorry there are no problems for student readers and glad I do not have to solve them, I recommend this book. Because of its good writing, its reliability, its choice of material, and its excellent degree of coverage, it is a good text for beginning annihilators and a handy reference for their professors.
