Nuclear, Particle and Many Body Physics

707 Pages·1972·33.047 MB·English

by  Philip Morse (Eds.)

Nuclear, Particle
and
Many Body Physics
Volume I
Editors
PHILIP M. MORSE
Massachusetts
Institute of Technology
Cambridge, Massachusetts
BERNARD T. FELD HERMAN FESHBACH RICHARD WILSON
Massachusetts Massachusetts N .
Institute of Technology Institute of Technology ian^fr nwer&ty
Cambridge, Massachusetts Cambridge, Massachusetts am ri ^e' assac usetts
Academic Press New York and London 1972
Copyright © 1972, by Academic Press, Inc.
ALL RIGHTS RESERVED
NO PART OF THIS BOOK MAY BE REPRODUCED IN ANY FORM,
BY PHOTOSTAT, MICROFILM, RETRIEVAL SYSTEM, OR ANY
OTHER MEANS, WITHOUT WRITTEN PERMISSION FROM
THE PUBLISHERS.
ACADEMIC PRESS, INC.
Ill Fifth Avenue, New York, New York 10003
United Kingdom Edition published by
ACADEMIC PRESS, INC. (LONDON) LTD.
24/28 Oval Road, London NW1 7DD
Library of Congress Catalog Card Number: 79-183529
The material in these volumes appeared in
ANNALS OF PHYSICS
Volume 63, Numbers 1 and 2, March and April 1971
Volume 66, Numbers 1 and 2, July and August 1971
Volume 69, Number 1, pp. 1-41, January 1972
THIS SOURCE SHOULD BE USED FOR REFERENCE CITATION
PRINTED IN THE UNITED STATES OF AMERICA
These volumes are dedicated to the memory of
Amos de-Shalit
and are published in cooperation with
the Weizmann Institute of Science
Preface
On January 15,1970 a letter of invitation to contribute to these volumes dedicated
to the memory of Amos de-Shalit was sent to his friends in the world of physics.
In part it said:
We know you join us in the feeling of great loss at the recent death of Amos
de-Shalit and in the desire to express the high regard and warm feelings
we all had for him. There will be many memorials. But to his fellow physicists
perhaps the most appropriate would be for each of us to dedicate one of our
more significant papers to his memory. With this in mind a volume of the
Annals of Physics dedicated to Amos de-Shalit and sponsored by the Weizmann
Institute of Science has been set aside. We invite you to contribute to this
volume. The volume will form a suitable memorial only if it consists of im­
portant contributions which will be referred to for many years. Such articles
are not plentiful but we hope that from Amos’ wide circle of friends a sufficient
number will be forthcoming.
The response to this invitation as contained in these two volumes forms an
extraordinary tribute to Amos. It is a measure of the respect he earned as a physic­
ist and of the warm and rich affection he commanded as a personal friend.
Amos had a vision of a possible future — a world in which knowledge would
be shared equally by men of all nations, developed and developing, great and
small. As he said knowledge is power — a power which should be used to create
a peaceful world, a world in which each life could be productive and satisfying.
It is a vision with which we can all agree — and toward whose realization we can
all contribute as he would have.
Sidney Drell
Herman Feshbach
Igal Talmi
ix
Eulogy
Amos de-Shalit was born in Jerusalem, September 29, 1926. He died of acute
pancreatitis September 2, 1969. In the 43 years of his life he made important and
lasting impressions in all fields in which he had been active. His death was the loss
of a leading figure in nuclear physics, of a mentor and guardian to physics in Israel
and of a friendly and helpful colleague to his many friends all over the world.
Anyone who met Amos was strongly impressed by his everlasting enthusiasm
for physics in particular and for any scientific achievement in general. His active
mind was always thinking about new ideas in physics as well as about various
projects to be planned and carried out. It is difficult to find words which will
describe his sparkling personality to those who were not fortunate to know him.
A successful attempt has been made by Professor Weisskopf, de-Shalit’s teacher,
colleague and friend. The present words are intended only to add a few features
to the image of Amos already portrayed so eloquently.
Considering the many accomplishments of Amos we realize that they could
have been achieved only by strong efforts of concentration. He had been busy
with matters that could easily occupy the full attention of several people. Yet he
had dealt with each of them with exceptional ability and dedication. His first year
at the Hebrew University of Jerusalem showed already a pattern typical of the
future. He was then a brilliant student while serving full time in the Jewish Settle­
ment Police — a military unit established by the British Mandate authorities
during World War II. His great capacity to concentrate enabled him later to carry
on significant research in nuclear physics while being, at the same time, Director
General of the Weizmann Institute and being involved in many other national
and international affairs.
Everything that Amos did was motivated by a deep sense of responsibility. He
felt very strongly the obligation of scientists to the society in which they live and
he believed that the privilege of being a scientist should not lead one to look
down on fellow humans. When explaining scientific matters to laymen, he could
make them share his enthusiasm and feel that they too can understand the im­
portance of science. They enjoyed being treated as equals in spite of the gap in
knowledge between them and the scientist. In such contacts he was very much
helped by his great personal appeal and the charm which he generously bestowed
on a charwoman equally well with the head of a state.
It was due to his sense of responsibility that he went into experimental physics
in Scherrer’s laboratory in the E.T.H. in Zurich. His interest was in theoretical
xi
xii EULOGY
physics which he studied with Giulio Racah in Jerusalem. His M.Sc. thesis was
on the self-energy problem in classical electrodynamics. Yet, in the end of 1949
after the War of Independence, when the newly born state of Israel decided to
send some of its best students to study abroad, de-Shalit chose to go into ex­
perimental physics. He felt that a good experimental program was essential to the
development of nuclear physics and was willing to undertake the assignment.
In Zurich he very soon became the leading figure in the group he joined and
supplied it with ideas and suggestions for new and exciting experiments. He easily
mastered the experimental techniques and even improved them considerably.
His most important contribution, however, was in choosing those experiments
which could throw some light on various aspects of nuclear structure.
Amos turned into theoretical work only later—during his stay at Princeton and
M.I.T. Yet his experience in experimental work had a profound influence on the
quality of his theoretical research. He was motivated by experiments and always
tried to point out what further avenues could or should be explored. Experimen­
talists could read and draw inspiration from his papers and even more from his
numerous invited talks at conferences. Yet more ideas were generously offered
by Amos during his frequent visits to many laboratories, in his lectures and
discussions. Thus, his work made a strong impact on nuclear research in many
institutions.
The organizational and administrative abilities of Amos de-Shalit attracted
early attention and in 1954 he was asked by the Weizmann Institute of Science
to establish and head a new department of nuclear physics. Amos himself was
aware of his abilities and could not refuse to carry the burden. In spite of the
strong interference which he encountered in his scientific work, he became a highly
successful leader of the new department which developed rapidly under his
guidance. Later he was called upon to serve as Director General of the Weizmann
Institute. He was a remarkable blend of a dreamer and a pragmatist. While
conceiving soaring ideas, he always remained on firm ground. He knew how to
bridge the gap between the desirable and the possible even though what seemed
possible to him sometimes seemed a mere dream to others until he made it a
reality.
He never forgot that institutions, like governments and nations, are composed
of people. Amos was particularly devoted to young scientists in whom he saw
the future of the Institute. He was always willing to listen to them and make them
feel that they belong. He was looking far ahead beyond the difficulties of the
present and this helped him keep the daily affairs in the proper perspective.
Amos’ activities were not confined to the Weizmann Institute nor to the state
of Israel. Though he was definitely a product of Israel, he felt at home in any
part of the world scientific community. He made a constant effort to demonstrate
that research in Israel is an integral part of the total scientific effort of the world.
EULOGY xiii
He tried to strengthen, as much as he could, the ties between scientists in different
countries and to promote international cooperation. In all these activities, Israeli
science could not have found a better representative.
Amos de-Shalit was an enthusiastic scientist, a leader in physics and of physicists,
a dedicated director of an institution who was involved in problems of society
in his country as well as internationally. He was a wonderful and rare combination
of talents. This makes the realization that he is no longer with us so difficult as
well as painful. We can only imagine, considering his many achievements how
much more he could have done and how much all of us have lost in his death.
Igal Talmi
Recollections of Amos de-Shalit
Victor F. Weisskopf
Department of Physics, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
November 2, 1970
“Amos, how wonderful to see you here again, always on trips around the world;
tell me, when are you actually working on physics?”
“Oh, on planes, in airports, I always find time. What are you working on right
now?”
“I am just trying to understand ..., to find out whether ..., to measure this quantity ...
under those conditions....”
“That’s a wonderful idea; I never thought of it this way. But isn’t there a possibility
to look at it differently?... let me see, what you are doing is really .... You know, your
idea is much better than I thought first, here we can get at the essential problem, if we
connect it with .... Look, shouldn’t that give us a better insight into ...? Let’s figure it out
together.... It’s actually much simpler than that .... Here we have it, that’s the way to
do it.... It’s beautiful! I’m so glad you told me this. You made me understand the problem
much better.”
This is a typical conversation which took place in some form or other many times,
in many offices, homes or laboratories when Amos de-Shalit was still alive and
traveling between the physics institutions of the world.
There are not many nuclear physicists, high or low energy, theoretical or experi­
mental, who never had discussions with Amos. In most of these encounters it was
his host who received new ideas, new suggestions for a better approach to the
problem and a deeper appreciation of the significance of his work.
Ever so often Amos pointed to the essential ideas and relations which were
hidden to his colleagues. His presence made a discussion more fruitful, a seminar
more instructive, and experiment more significant. When he visited a laboratory
or a department, the level of activity was markedly increased. He raised questions,
he challenged ideas, he brought life and excitement. It was not only his great
knowledge which had this effect; it was his readiness to listen and to follow the
work of others, his openness to questions, his interest in any thought or idea,
even if it was not in his special field; but foremost, his enthusiasm for every new
insight and his ability to recognize the significance of an idea. So many of his
friends have had his help in developing their own ideas, a help which he gave
xv
xvi RECOLLECTIONS OF AMOS DE-SHALIT
freely and unsparingly. More often than not, he supplied the ideas and suggestions
which later developed into successful theories or experiments of others. When he
visited laboratories—and he did this copiously—he left behind a trail of intellectual
seed. Long is the list of papers which were spawned by his remarks and suggestions.
He created a large community of friends at every place where nuclear science is
alive, and each of his friends owes him some gift which has enriched his insight and
increased his intellectual joy with physics. The size and content of the present
volume of the Annals of Physics shows how wide spread this community is,
intellectually and geographically.
The work published under de-Shalit’s name is only a part of his contribution
to physics. Nevertheless, it represents a most significant achievment, ranking him
among the most brilliant physicists. He belongs to the very few modern physicists
who are both experimentalists and theorists. He began his experimental work at
Zurich in the Institute of P. Scherrer. His extensive work in Switzerland, whicWhe
later continued at the Weizmann Institute, was mainly concerned with radioactive
nuclei and their various decay modes. He invented new methods of observation
and improved the precision of measurements, which served to expand the range of
nuclear spectroscopy. Later on he kept up his interest in experimental nuclear
physics, but his main work shifted to theory. His close touch with experiments
gave a special character to his theoretical work. He was better able than many
others to interpret experimental results and keep theory from becoming too
speculative. In particular, his papers on the interpretation and application of the
shell-model of the nucleus were of fundamental importance for the understanding
of the significance of this model, but also for the recognition of its inherent
limitations.
The topics of de-Shalit’s publications are spread over all parts of modern physics,
but a consideration of the publications alone would be insufficient to describe his
role and his influence as a physicist. Amos de-Shalit was a man who created
contacts, contacts between ideas, contacts between fields of physics, contacts
between physicists, between nations, and between the scientists and the rest of the
world. By this ability to listen in discussions and to see the problems clearer than
others, he brought together scientists working in the same field. By his wide
horizon and interest in everything that has to do with physics he established
contacts between different fields of physics. He did his utmost and was successful
in bringing nuclear physics and particle physics together again after they parted
ways and fell into the parochial ruts of specialization. Through his initiative, regular
meetings are now held every second year, devoted to the common problems of
these two fields which are dependent on each other to a larger extent than atomic
and molecular physics. Sadly enough, many specialists do not seem to be aware
of this.
He brought the physicists of all nations nearer to each other by his personal
WEISSKOPF xvii
relations and by his activities in many international scientific organizations. The
creation of human contacts was part of his life. He was active in the councils of
the Internation Union of Pure and Applied Physics, in the Pugwash meetings and
at all places where physics serves as a bond between people. He also worked hard
at the thorny problem of how to help developing countries through technical aid
and advice. Not long before his death he organized at the Weizmann Institute a
Conference on Science and Education in developing states, in which he played a
leading part in formulating the conditions under which such aid and advice can be
useful and successful. This was another example of his efforts to improve con­
ditions by establishing human contacts between people.
He was one of those few personalities who are liked and respected by everyone.
He had an instinctive gift of inspiring authority without enforcing it. With these
human qualities he could not avoid being drawn into important administrative
positions. This is why he was asked to be the head of the physics department and
later on, to be the Scientific Director of the Weizmann Institute. He never refused to
serve when he knew he could do well, although his time to do real physics was
severely curtailed by these duties. He succeeded in building one of the best physics
departments in the world under difficult conditions in an astonishinly short period:
A good example of what one can do at places far removed from the centers of
science.
One of Amos’ greatest strengths was his wide and open interest in everything that
had to do with science. One could talk to him about any topic of physics and he
would take up the problem with enthusiasm and with an insight which does not
come from special expert knowledge, but from a deep understanding of the real
meaning of physics. His attitude was the opposite of the spirit of over-specialization
which pervades modern science. The technical and mathematical tools of science
are becoming so formidable and so complicated that many scientists do not find
enough time and strength for thinking beyond the immediate applications of
those tools. The tools should be a means toward a goal and not an end in them­
selves. The true goal of science must be the discovery of the basic laws of nature
and the clarification of the essential features of natural phenomena. The basic
traits of nature should be simple; if they lose their simplicity, the idea of science
has gone astray. The ways to get at the fundamentals have become complicated
in modern science, but not the fundamentals themselves. These are the ideas which
dominated Amos de-Shalit’s thinking and acting. Certainly he was an expert in
some of the most complicated mathematical techniques of atomic and nuclear
physics; this emerges clearly from many of his papers and from his book with
I. Talmi on “Nuclear Shell Theory.” But he never lost sight of the intrinsic
simplicity and beauty of the essential points. He had that strong urge to communi­
cate the essentials of physics to others and to transmit his joy of understanding to
students and fellow scientists. His enthusiasm and his personal warmth made him