66952 CD CO OSMANIA UNIVERSITY LIBRARY Call No. 53?.f/Jj *j$flAccession No, Author This book should be imied on or before the date last maited below. NUCLEAR FISSION AND ATOMIC ENERGY NUCLEAR FISSION and ATOMIC ENERGY by WILLIAM E. STEPHENS (editor) and PARK HAYS MILLER, JR. BERNARD GOODMAN KNUT KRIEGER WALTER E. MEYERHOF MARGARET N. LEWIS BERNARD SERIN SIMON PASTERNACK ROBERT H. VOUGHT Members of the Staff of the University of Pennsylvania THE SCIENCE PRESS Lancaster, Pa. 1948 Copyright, 1946, 1948 by WILLIAM E. STEPHENS All rights reserved FEINTED BY THE DARWIN PRESS NEW BEDFORD, MASS. CONTENTS Page Foreword vii Editor's Preface ix Chapter 1. Discovery of Fission 1 2. Production of Fission 6 3. Fission Fragments 16 4. Fission Products 22 5. Secondary Neutrons 43 6. Heavy Nuclei 50 7. Theory of Fission 67 8. Dynamics of Fission 92 9. Early Work on Chain Reactions 117 10. Slow Neutron Chain Reactions Piles 133 11. Fast Neutron Chain Reaction 171 12. Separation of Isotopes 181 13. Chemical Separation Methods: Isolation of Plutonium 222 14. Potentialities of Fission Techniques 234 Bibliography <... 259 ' Author Index : 281 Subject Index : 287 FOREWORD FREE and unrestricted research in nuclear physics ceased abruptly in 1941. Activity in the field went underground and certain aspects were the subject of intense study and investigation in secret under the forced draft of military urgency and unlimited support. It emerged on August 6, 1945, with the most destructive explosion that has ever been produced by man. The same dra- matic event answered affirmatively the outstanding question which had engaged nuclear physicists previously : Is a self-sustaining nu- clear chain reaction possible? The successful culmination of the work of the Manhattan District in the explosion of the bombs over Japan punctuated the end of the war and announced the scientific fact that nuclear chain reactions could be brought about. With the cessation of hostilities nuclear physicists have re- turned from a wide variety of war research assignments to this, their chosen field. The obvious first step in resuming programs of fundamental research has been a review of the literature and a taking of scientific stock in the light of available information. At the University of Pennsylvania a series of seminars was conducted by Dr. Stephens and the staff of the Department of Physics resi- dent in the autumn of 1945, for the purpose of reviewing all freely available information and reorienting the interests of the research group. The extensive examination of all the pertinent literature at their disposal and the careful study of its implications in the light of present common scientific knowledge has been of great value in the planning of a research program at the University of Pennsylvania. It is in the hope that the efforts of this group may serve a much broader purpose in assisting their scientific col- leagues elsewhere to resume their research programs or enable them to enter their field of fundamental investigation that these seminar notes have been edited for publication. Unfortunately this book perforce marks a departure from traditional scientific publications, a departure which it is hoped is only a temporary result of abnormal post-war conditions. The authors of this book, in common with authors of reviews in other branches of physical science, have dealt only with information that is available to all. But unlike authors of pre-war treatises they are aware that there exists a body of pertinent knowledge inaccess- ible to them. To avoid any possible imputation of inadvertent breach of security they have been at pains not to discuss these topics with any persons in possession of classified knowledge con- cerning them. Though a more complete book on the subject might be written by men who have participated in the atomic bomb proj- ect, such persons are at present legally precluded from such an undertaking. The very ignorance of the authors of this book thus enables them to contribute their special training to the writing of it as a contribution to the advancement of knowledge in the best scientific tradition. There is nothing herein tnat any physicist, be he American, English, Russian, French, Indian or Chinese, could not already know if he himself had taken the time to rework the excellent report of Dr. H. D. Smyth and the recent literature of physics with nuclear fission in mind. Nuclear physics involves a considerable number of concepts which are not familiar through common experience. This fact, together with the necessarily mathematical nature of the theoreti- cal analyses and the formulation of results, renders the subject a peculiarly difficult one for persons untrained in this science. This situation undoubtedly has led to much popular misunderstanding in the matter of security and has contributed to loose and hasty thinking about supposed secrets which Nature is thought to have shared with this country alone. In a sense the fact that this book could be written by physicists having access to no material not freely available to scientists the world over makes it clear that Nature is the only possible guardian of her own secrets. A sincere effort is being made to bring about a popular clari- fication of these matters in order that the advancement of knowl- edge may not be legally interdicted in this country to the great detriment of our national well being. The achievements of gen- erations of free scientists, which chiefly differentiate our life from that of the dark ages, are the best arguments for the preservation of freedom of intellectual inquiry. This book documents the thesis that the understanding of nafhral phenomena, of which nuclear fission is no exceptional instance, can be gained by any trained and inquiring mind. Nature will not be a party to man's attempt at discrimination between nations, races or individuals. If the pub- lication of this book contributes to the general appreciation of this fact it will have performed an important additional service in clear- ing away erroneous conceptions and in promoting a wiser and more constructive approach to current national problems. April 15, 1946 G. P. HARNWELL Chairman, Department of Physics, University of Pennsylvania viii EDITOR'S PREFACE THIS book originated in a series of seminars on nuclear fis- sion held in the Physics Department of the University of Pennsyl- vania in the fall of 1945. These seminars reviewed the known facts of nuclear fission as published in the literature. The notes were mimeographed from week to week and formed a record of the dis- cussions. Because of the interest expressed by other physicists, we have been persuaded to publish the material. We hope that this book will enable physicists who, like most of the authors, are not specialists in nuclear physics, to obtain a semiquantitative understanding of the phenomena concerned. The persons who presented the seminars and wrote the vari- ous chapters have had no connection with the Manhattan District project. All were on the staff of the University of Pennsylvania. The seminar speakers and their topics in order of presentation were: MARGARET N. LEWIS " Transuranic * ' Elements WILLIAM E. STEPHENS Fission Fragments EGBERT H. VOUGHT Fission Products BERNARD SERIN Secondary Neutrons BERNARD GOODMAN Theoretical Considerations WALTER E. MEYERHOF Isotope Separation SIMON PASTERNACK Controlled Chain Reaction* Piles. KNUT KRIEGER Chemistry of Plutonium PARK HAYS MILLER, JR Atom Bomb WILLIAM E. STEPHENS Potentialities of Fission Technique We wish to thank Prof. L. A. Turner, Prof. J. A. Wheeler, and Dr. T. Lauritsen for consenting to the reproduction of their work, and to acknowledge our indebtedness to the excellent re- view article by Professor Turner, Rev. Mod. Phys. 12, 1 (1940), to the classic paper by Bohr and Wheeler, Phys. Rev. 56, 426 (1939), and to the comprehensive report of H. D. Smyth, Rev. Mod. Phys. 17, 351 (1945). April 15, 1946 WILLIAM E. STEPHENS. Owing to difficulties of publication, the appearance of this book has been delayed far beyond the date originally hoped for. Subsequent to the preparation of manuscript and its initial distri- bution in mimeographed form, much information on details of the fission process, fission products, and heavy nuclei was released and published in scientific periodicals. However, the main ideas con- tained in this book were not essentially changed thereby, although some details need to be corrected and many details added. Con- sequently, we have added a supplementary bibliography of publi- cations that came to our attention after the manuscript was pre- pared and before October, 1947. November 15, 1947 W. E. S. CHAPTER 1 DISCOVERY OF FISSION The explosions at Hiroshima and Nagasaki demonstrated to the public for the first time that successful nuclear chain reactions could be produced by man. The discovery of the fission of the uranium and thorium nuclei in 1939 and the subsequent observa- tions which showed that several secondary neutrons were emitted in the process had given evidence that such a reaction might be produced. The story of this discovery of fission and the recogni- tion of the tremendous energy released in the process forms one of the most fascinating chapters in physics. It was the discovery of the neutron by Chadwick in 1932 that prompted Fermi to search for transuranic elements in the products of uranium and thorium bombarded by neutrons, thereby starting the chain of events leading to the discovery of fission. The com- plicated processes which occurred were not understood at first, and the years which followed the publication of Fermi's original paper found several groups of workers in different countries trying to understand what had happened. This problem was finally re- solved by the observation by Hahn and Strassmann of the exist- ence of a light element among the products of uranium bombarded by neutrons and by the insight of Meitner and Frisch into the tre- mendous energy evolved in the process.