Bruce Cameron Reed - The Physics of the Manhattan Project

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To readers who have purchased this and possibly earlier editions of this book, I thank you. Your support, suggestions, comments, and criticisms have made each edition better than the preceding one. This will likely be the final edition of The Physics of the Manhattan Project, and it incorporates a number of revisions, various new graphs, four new sections, updated data, and clarifications and corrections of a number of points. These revisions reflect my own increased knowledge of the subject matter and a number of helpful suggestions contributed by readers who took time to contact me.

The fact that you are reading this indicates that you appreciate that the discovery of nuclear energy and its liberation via nuclear weapons was one of the pivotal events of the twentieth century. The strategic and military implications of this development drove much of cold-war geopolitics for the last half of that century, and remain with us today in the form of weapons stockpiles and deployments, proliferation, fissile-material security concerns, test-ban treaties, and concern with the possibility that terrorists or unstable international players might be able to acquire enough fissile material to assemble a crude nuclear weapon. For better or worse, stabilizing or destabilizing, the legacies of the United States Armys Manhattan Engineer District, Los Alamos, Oak Ridge, Hanford, Trinity, Little Boy, Fat Man, Hiroshima, and Nagasaki will continue to influence events for decades to come, even as the number of deployed nuclear weapons in the world declines.

To sensibly assess information and claims regarding these concerns, one needs some knowledge of the physics that backgrounds nuclear weapons. Should you be merely concerned or downright alarmed if you learn that a potential adversary country is enriching uranium to 20% 235U or developing fuel-rod reprocessing technology? Why is there is such a thing as a critical mass, and how can one estimate it? How does a nuclear reactor differ from a nuclear weapon? Why cant a nuclear weapon be made with a common metal such as aluminum or iron as its active ingredient? How did the properties of various uranium and plutonium isotopes lead to the development of the gun and implosion weapons used at Hiroshima and Nagasaki? How did the developers of those devices estimate their expected energy yields? How can you arrange to assemble a critical mass in such a way as to avoid blowing yourself up beforehand? This book is an effort to address such questions at about the level of a junior-year undergraduate physics student.

This work grew out of three courses that I taught at Alma College, supplemented with information drawn from a number of my own and other published research articles. One of the courses was a conventional undergraduate sophomore-level modern physics class for physics majors which contained a unit on nuclear physics. Another was an algebra-level general-education class on the history of the making of nuclear weapons in World War II, and the third was a junior-level topics class for physics majors that used much of the present volume as its text. What originally motivated this book was that there seemed to be no one source available for a reader with a college-level background in physics and mathematics who desired to learn something of the technical aspects of the Manhattan Project in more detail than is typically presented in conventional texts or popular histories. As my own knowledge of these issues grew, I began assembling a collection of derivations and results to share with my students, and which evolved into the present volume. I hope that readers will discover, as I did, that studying nuclear weapons is not only fascinating in its own right, but is an excellent vehicle for reinforcing understanding of many foundational areas of physics such as energy, electromagnetism, dynamics, statistical mechanics, modern physics, and, of course, nuclear physicsas well as their attendant mathematical techniques.