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In the present volume and in the preceding one we have stretched
our normal pattern of reviews by including articles of more major
proportions than any we have published before. As a consequence
each of these two vol umes contains only three review articles.
From the beginning of this series it has been our aim, as editors,
to achieve variation in the scope, style, and length of individual
articles sufficient to match the needs of the individual topic,
rather than to restrain the authors within rigid limits. We feel
that the two major articles of Vols. 5 and 6 are entirely justified
and do not repre sent unnecessary exuberance on the part of the
authors. The article by Michaudon on fission is the first
comprehensive account of the developments in this subject, which
have placed it in the center of the stage of nuclear physics during
the past few years. The discovery of fission isomerism and its
dramatic manifestations in the intermediate structure of the
neutron cross sections for fissionable isotopes are among the most
im portant and interesting events to occur in nuclear physics.
These events came as a surprise, and reaffirmed that the strength
of nuclear physics lies in the combination of ingenious experiments
with simple ideas.
With the appearance of Volume 3 of our series the review articles
them selves can speak for the nature of the series. Our initial aim
of charting the field of nuclear physics with some regularity and
completeness is, hopefully, beginning to be established. We are
greatly indebted to the willing coopera tion of many authors which
has kept the series on schedule. By means of the "stream" technique
on which our series is based - in which articles emerge from a flow
of future articles at the convenience of the authors-the articles
appear in this volume without any special coordination of topics.
The topics range from the interaction of pions with nuclei to
direct reactions in deformed nuclei. There is a great number of
additional topics which the series hopes to include. Some of these
are indicated by our list of future articles. Some have so far not
appeared on our list because the topics have been reviewed re
cently in other channels. Much of our series has originated from
the sug gestions of our colleagues. We continue to welcome such aid
and we continue to need, particularly, more suggestions about
experimentalists who might write articles on experimental topics."
As much by chance as by design, the present volume comes closer to
having a single theme than any of our earlier volumes. That theme
is the properties of nuclear strength functions or, alternatively,
the problem of line spreading. The line spreading or strength
function concepts are essential for the nucleus because of its many
degrees of freedom. The description of the nucleus is approached by
using model wave functions-for example, the shell model or the
collective model-in which one has truncated the number of degrees
of freedom. The question then is how closely do the model wave
functions correspond to the actual nuclear wave functions which
enjoy all the degrees of freedom of the nuclear Hamiltonian? More
precisely, one views the model wave functions as vectors in a
Hilbert space and one views the actual wave functions as vectors
spanning another, larger Hilbert space. Then the question is: how
is a single-model wave function (or vector) spread among the
vectors corresponding to the actual wave functions? As an example
we consider a model state which is a shell-model wave function with
a single nucleon added to a closed shell. Such a model state is
called a single-particle wave function. At the energy of the
single-particle waVe function one of the actual nuclear wave
functions may resemble the single-particle wave function closely.
The present volume reaffirms nuclear physics as an experimental
science since the authors are primarily experimentalists and since
the treatment of the topics might be said to be "experimental."
(This is no reflection on the theoretical competence of any of the
authors.) The subject of high-spin phenomena in heavy nuclei has
grown much beyond the idea of "backbending" which gave such an
impetus to its study five years ago. It is a rich, new field to
which Lieder and Ryde have contributed greatly. The article
"Valence and Doorway Mechanisms in Resonance Neutron Capture" is,
in contradistinction, an article pertaining to one of the oldest
branches of nuclear physics-and it brings back one of our previous
authors. The Doppler-shift method, reviewed by Alexander and
Forster, is one of the important new experimental techniques that
emerged in the previous decade. This review is intended,
deliberately, to describe thoroughly a classic technique whose
elegance epitomizes much of the fascination which nuclear physics
techniques have held for a generation of scientists. This volume
concludes the work on the Advances in Nuclear Physics series of one
of the editors (M. Baranger), whose judgment and style characterize
that which is best in the first ten volumes. Many of our readers
and most of our authors will be grateful for the high standards
which marked his contributions and which often elicited extra labor
from the many authors of the series.
The aim of Advances in Nuclear Physics is to provide review papers
which chart the field of nuclear physics with some regularity and
completeness. We define the field of nuclear physics as that which
deals with the structure and behavior of atomic nuclei. Although
many good books and reviews on nuclear physics are available, none
attempts to provide a coverage which is at the same time continuing
and reasonably complete. Many people have felt the need for a new
series to fill this gap and this is the ambition of Advances in
Nuclear Physics. The articles will be aimed at a wide audience,
from research students to active research workers. The selection of
topics and their treatment will be varied but the basic viewpoint
will be pedagogical. In the past two decades the field of nuclear
physics has achieved its own identity, occupying a central position
between elementary particle physics on one side and atomic and
solid state physics on the other. Nuclear physics is remarkable
both by its unity, which it derives from its concise boundaries,
and by its amazing diversity, which stems from the multiplicity of
experimental approaches and from the complexity of the
nucleon-nucleon force. Physicists specializing in one aspect of
this strongly unified, yet very complex, field find it imperative
to stay well-informed of the other aspects. This provides a strong
motivation for a comprehensive series of reviews.
In both the present volume of Advances in Nuclear Physics and in
the next volume, which will follow in a few months' time, we have
stretched our normal pattern of reviews by including articles of
more major proportions than any we have published before. As a
result we have only three review articles in Volume 5. From the
beginning of this series it has been our aim, as editors, to
achieve variation in the scope, style, and length of individual
articles sufficient to match the needs of the individual topic,
rather than to restrain authors within rigid limits. It has not
been our experience that this flexibility has led to unnecessary
exuberance on the part of the authors. We feel that the major
articles now entering the series are entirely justified. The
article by Professor Delves on "Variational Techniques in the
Nuclear Three-Body Problem" is an authoritative, definitive article
on a subject which forms a cornerstone of nuclear physics. If we
start with two body interactions, then the three-nucleon system is,
perhaps, the only many nucleon system whose exact description may
lie within the scope of human ingenuity. In recent years some new
techniques of scattering theory, origi nating mostly in particle
physics, have led to a great deal of new interest in the nuclear
three-body problem. In this series we have had two articles (by
Mitra and by Duck) on the new approaches."
The aim of Advances in Nuclear Physics is to provide review papers
which chart the field of nuclear physics with some regularity and
completeness. We define the field of nuclear physics as that which
deals with the structure and behavior of atomic nuclei. Although
many good books and reviews on nuclear physics are available, none
attempts to provide a coverage which is at the same time continuing
and reasonably complete. Many people have felt the need for a new
series to fill this gap and this is the ambition of Advances in
Nuclear Physics. The articles will be aimed at a wide audience,
from research students to active research workers. The selection of
topics and their treatment will be varied but the basic viewpoint
will be pedagogical. In the past two decades the field of nuclear
physics has achieved its own identity, occupying a central position
between elementary particle physics on one side and atomic and
solid state physics on the other. Nuclear physics is remarkable
both by its unity, which it derives from its concise boundaries,
and by its amazing diversity, which stems from the multiplicity of
experimental approaches and from the complexity of the
nucleon-nucleon force. Physicists specializing in one aspect of
this strongly unified, yet very complex, field find it imperative
to stay well-informed of the other aspects. This provides a strong
motivation for a comprehensive series of reviews.
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