Bohr's first acquaintance with the subject of penetration of charged particles through matter was as early as in 1912 when he treated the absorption of &agr; and &bgr; rays on the basis of Rutherford's atomic model. From then on he kept a lifelong interest in the subject, often using it as an important test of the methods of atomic mechanics. His last paper on penetration, written together with Jens Lindhard, dealt with electron capture and loss and was published in 1954.Part I of this volume follows Bohr's work on penetration theory based on classical mechanics. Part II deals with the general theory of penetration, taking quantum-mechanical considerations into account.

Niels Bohr: Collected Works, Volume 13: Cumulative Subject Index documents aspects of Niels Bohr's varied life and work in the form of a cumulative subject index, with emphasis on his scientific contributions in the field of physics. The general organization of the material is thematic rather than strictly chronological, allowing for the presentation of each paper (or group of papers) along with other relevant material such as drafts, notes, letters, and other items. The book is illustrated with rare photos and includes explanatory notes as well as a bibliography. The bibliography is restricted to the versions of Bohr's publications reproduced in this volume and encompasses a wide range of topics in physics, from the determination of the surface tension of water by the method of jet vibration to the electron theory of metals and of thermoelectric phenomena; the theory of the decrease of velocity of moving electrified particles on passing through matter; the constitution of atoms and molecules; and the spectra of helium and hydrogen. Bohr's other papers focus on the effect of electric and magnetic fields on spectral lines; the quantum theory of radiation and the structure of the atom; the polarization of radiation in the quantum theory; and collisions between atomic systems and free electrical particles. This monograph will be useful to students, practitioners, and researchers interested in Bohr's life and work in general and in quantum mechanics in particular.

The Niels Bohr Collected Works are now complete with the publication of Volume 12, Popularization and People (1911-1962).Niels Bohr is generally regarded as one of the most influential physicists of the twentieth century. The following are only some of the high points. In 1913, Bohr proposed a revolutionary model of the atom breaking with classical conceptions of physics. In 1921, he established the Institute for Theoretical Physics at the University of Copenhagen, which became the centre for the new physics visited by the younger generation of physicists from all over the world. From 1927, he oversaw the development leading to the "Copenhagen interpretation" of quantum mechanics which for Bohr formed the foundation for an epistemology valid beyond physics based on Bohr's complementarity concept. In 1939, he explained the mechanism of nuclear fission. Finally, from 1943 until the end of his life in 1962, he carried out a personal political mission to establish an open world between nations which he considered to be necessary in view of the existence of the atomic bomb.All these contributions are amply documented in the earlier volumes of the Niels Bohr Collected Works. This last volume documents Niels Bohr as a person and his efforts to explain quantum physics and its implications to physicists and non-physicists alike. While his activity over many years in the area of superconductivity illustrates his striving for synthesis in physics, his encyclopaedia articles and radio speech for Scandinavian gymnasium students document his effort to make quantum physics and its implications understandable to the general public. The bulk of the volume comprises Bohr's many published writings about his predecessors (for example Isaac Newton), teachers and colleagues (for example Ernest Rutherford and Albert Einstein), family and friends. These writings, which include several rare pieces of autobiogaphy, bring new perspectives to Bohr's life and document his substantial social network, both internationally and within his beloved Denmark.In addition to Bohr's publications reproduced in Parts I and II, the volume includes a more brief Part III with selected correspondence, as well as an inventory of relevant manuscripts. It concludes with a bibliography of Bohr's many publications, chronologically arranged with references to where they can be found in the various volumes of the Collected Works. The volume is illustrated with many new photographs.* Niels Bohr * Collected Works * Archival Documents * Original Photographs

Across decades and disciplines, More than Nothing offers a scoping history of the vacuum as a lens into the development of modern physics.

How and why do complex scientific disciplines such as physics change emphasis from one sub-discipline to another? Do such transitions stem entirely from developments within the discipline itself or also from external factors? This book addresses these questions by examining the transition from atomic to nuclear physics, theoretically and experimentally, at Niels Bohr’s Institute for Theoretical Physics in Copenhagen in the 1930s. On the basis of extensive archival research, Finn Aaserud shows that the “Copenhagen spirit,” the playful research atmosphere under Bohr’s fatherly guidance that permeated the Institute, thrived because of extra-scientific circumstances that Bohr exploited to the fullest, such as the need to help Jewish physicists out of Hitler’s Germany and the changing funding policies of private foundations, notably those of the Rockefeller Foundation which made it opportune to introduce research in experimental biology at the Institute. “A clear, carefully developed and substantially convincing argument... Aaserud gives a detailed and impressively documented account of the direction of Bohr’s scientific interests... Aaserud is... to be congratulated for his original, clear — indeed, didactic — work of scholarship and enlightenment.” — Paul Forman, Physics Today “A professional historian’s study of the happenings at the Niels Bohr Institute in the decisive years 1930 to 1940... In particular, the... support of the Institute by Danish and other foundations, mainly the Rockefeller Foundation, are treated in great detail, revealing many interesting aspects of these relationships... The detailed accounts... of Bohr’s negotiations are a testimony to Bohr’s uncanny ability to get what he wanted from the various foundations... Aaserud’s book is an invaluable source of information [showing] that Bohr was not only an inspiring physicist and philosopher but also a cunning negotiator who knew how to make use of his great reputation for the benefit of science.” — Victor F. Weisskopf, Science “Aaserud elucidates Bohr’s skills not only as mentor and guiding hand behind the ‘Copenhagen spirit,’ but also as financial negotiator.” — Neil Wasserman, Isis, A Journal of the History of Science Society “This book teaches us that running such [a truly elite] institution required entrepreneurial skills as well as scientific genius. Bohr had an abundance of both.” — Jeremy Bernstein, Nature “Redirecting Science is the history of Bohr’s institute during the 1930s when it experienced a drastic change in its research priorities, from a laissez-faire mode of work and lack of clearly defined research programme to a concerted research effort in nuclear physics and experimental biology... Aaserud gives a highly interesting account of the interaction between physics and biology... Aaserud’s carefully documented work is an excellent example of how institutional history may transcend social and institutional limitations and integrate also conceptual history of science.” — Helge Kragh, Centaurus “By showing that a new research programme at one of the most important scientific institutes in the world was triggered, and pushed forward, by social and financial considerations, this book delivers yet another blow to the tired old idea that scientific knowledge is driven by its own internal, inexorable logic. It also throws valuable light on Bohr’s activities and strategies as a fundraiser and institution builder.” — John Krige, The British Journal for the History of Science