Nuclear Superfluidity. Pairing in Finite Systems, by D.M. Brink and R.A. Broglia
Nuclear Superfluidity. Pairing in Finite Systems, by D.M. Brink and R.A. Broglia, Cambridge, Cambridge University Press, 2005, xiv + 378 pp., £80.00 (hardback), ISBN 0521395402. Scope: textbook. Level: specialist, postdoctoral and postgraduate.
Nuclear structure physics is currently experiencing a renaissance. Recent technical developments have made possible the acceleration of well-defined beams of radioactive nuclei with numbers of neutrons (N) and protons (Z) far from the valley of stability in the N–Z plane where nuclei found on Earth lie. These exotic nuclei frequently play a key role in nuclear reactions in stars and understanding their structure is an important part of the quest to understand the way elements crucial to life on Earth are created in the Universe. New facilities at major laboratories in Europe, Asia and North America will be dedicated to research with radioactive ion beams which will address this issue and also explore the application of exotic nuclear species in medicine and condensed matter physics. The subject of this timely book is modern theories of nuclear structure and the fundamental basis which underpin them.
The book surveys some of the most important insights that have been developed by theorists to understand nuclei as a many-body system of interacting neutrons and protons. The title of the book suggests a rather restricted scope, but in fact it addresses a wide selection of the varied phenomena observed in the spectra of atomic nuclei and how modern nuclear theory makes sense of them. The unifying theme chosen by the authors is the ‘pairing’ property of the short range strong interaction between nucleons.
The special theoretical techniques that become available when the force between any pair of particles acts only between time-reversed quantum states (pairing theory) was first recognised and exploited in the theory of superconductivity in metals by Bardeen, Cooper and Schrieffer. Their work dealt with systems of very large numbers of particles interacting through long range electromagnetic forces. Nuclei are very small and have properties that can be very sensitive to the precise number of interacting nucleons involved. Nevertheless, nuclei display many phenomena which can be usefully discussed by adapting pairing theory to the very short-range forces acting between a finite number of nucleons in a small, essentially spherical, region of space.
There are, of course, many important differences between nuclear and condensed matter pairing phenomena. It is one of the nice features of this book that it explains the fundamental basis for these differences within a coherent framework. The authors are well qualified to perform this task, both of them having individually made important contributions to nuclear structure theory.
This is a formidable book. There must be few theoretical nuclear physicists who have the expertise to feel at home in all the sections of the book. The Introduction is written from an elevated intellectual standpoint that the present reviewers found quite inappropriate for an introduction. We were not helped by the misprints and undefined quantities to be found in several parts of this chapter. Beginning researchers in nuclear physics may be intimidated by this and some other sections and as a result may not persevere and uncover the gems elsewhere. This would be a pity because the book gives a detailed account of what is actually involved in carrying out calculations based on the principles with great clarity. Chapters 2 and 3 give an excellent exposition of the basic application of pairing theory to nuclear physics at a level that any theoretical nuclear physics Ph.D. student would find rewarding and be expected to master.
Chapter 4 contains an illuminating discussion of how pairing theory fits into the general concept of spontaneous symmetry breaking. There follow two chapters on pairing vibrations and phase transitions. The question of the source of pairing forces in nuclei and their relation with the forces deduced from nucleon–nucleon scattering experiments is discussed in Chapters 8, 9 and 10, where the important role of coupling to vibrations of the finite nuclear surface in renormalising the bare nucleon–nucleon interaction is emphasised. Chapter 10 also discusses superfluidity in the inner crust of neutron stars.
The final chapter in the book is devoted to the structure of nuclei near the neutron and proton drip lines. These are the loci in the N–Z chart of nuclides of those isotopes and isotones which are stable against nucleon emission (although not against the weak interaction) and which have the largest number of neutrons and protons, respectively. This subject is at the forefront of recent research in nuclear structure. The main emphasis is on recent work by the Milan group on the ‘halo’ nuclei 11Li and 12Be where two neutrons form a low-density cloud around a tightly bound core. The Milan work emphasises the crucial role of multipole vibrations in producing the observed halo structure.
This book is an important addition to the fundamental physics literature. A good background in basic concepts of nuclear theory, including the shell and collective models is a prerequisite, and, for some sections, knowledge of certain techniques in the theory of direct nuclear reactions is required. Thus, fore-armed, the dedicated reader will come away from this work richly rewarded.
© 2010, R.C. Johnson and M. Oi