1. Overview
Ben Roy Mottelson (July 9, 1926 - May 13, 2022) was an American-Danish nuclear physicist who made groundbreaking contributions to the understanding of the atomic nucleus. He was jointly awarded the Nobel Prize in Physics in 1975 for his work on the non-spherical geometry of atomic nuclei and for developing the theory of nuclear structure based on the connection between collective and particle motion within the nucleus. His career was marked by significant research collaborations, particularly with Aage Bohr and James Rainwater, and his commitment to international scientific cooperation.
2. Early Life and Education
Ben Roy Mottelson's formative years and academic journey laid the groundwork for his distinguished career in theoretical physics.
2.1. Childhood and Education
Ben Roy Mottelson was born in Chicago, Illinois, United States, on July 9, 1926. His parents were Goodman Mottelson, an engineer, and Georgia (Blum). His family was Jewish. He attended Lyons Township High School in La Grange, Illinois. After graduating from high school, he joined the United States Navy and was sent to Purdue University for officer training, where he earned his Bachelor of Science degree in 1947. He then pursued his doctoral studies at Harvard University, receiving his Ph.D. in nuclear physics in 1950. His doctoral thesis advisor was Julian Schwinger, a prominent theoretical physicist who would later win the Nobel Prize in Physics in 1965 for his work on quantum electrodynamics.
3. Career and Research
Mottelson's professional career was largely centered in Denmark, where he made his most significant scientific contributions. He held various academic appointments and engaged in pivotal research activities that reshaped the field of nuclear physics.
3.1. Research Activities in Copenhagen
Following his doctoral studies, Mottelson moved to Copenhagen, Denmark, on a Sheldon Traveling Fellowship from Harvard University. He began his post-doctoral work at the Institute for Theoretical Physics, which later became known as the Niels Bohr Institute. It was here that he commenced his influential collaboration with Aage Bohr, the son of the renowned physicist Niels Bohr. Their joint efforts focused on comparing theoretical nuclear models with experimental data. In 1950-1951, James Rainwater and Aage Bohr had developed initial models of the atomic nucleus that began to account for the behavior of individual nucleons, moving beyond the simpler liquid drop model which treated the nucleus as having no internal structure. These new models were the first to explain various nuclear properties, including the non-spherical distribution of charge in certain nuclei.
Mottelson worked closely with Aage Bohr to refine these theoretical models and validate them against experimental observations. Between 1952 and 1953, Bohr and Mottelson published a series of seminal papers demonstrating a close agreement between their theoretical framework and experimental results. For instance, they showed that the energy levels of certain nuclei could be accurately described by a rotational spectrum. This groundbreaking work stimulated numerous new theoretical and experimental studies in nuclear physics. In the summer of 1957, David Pines visited Copenhagen and introduced Bohr and Mottelson to the pairing effect concept, which had been developed in theories of superconductivity. This inspired them to introduce a similar pairing effect to explain the differences in energy levels observed between even and odd atomic nuclei, publishing a paper on this analogy in 1958 with Pines. Their work led to the construction of the collective model in 1953, which unified the description of independent particle motion, typically described by the shell model, with the collective motion of nucleons, previously described by the liquid drop model. Mottelson's subsequent research continued to yield significant achievements in the microscopic theory of collective motion, including the observation of the emergence of a superfluid state in atomic nuclei in 1958, following the proposal of the BCS theory. He also suggested the possibility of a phase transition from a superfluid to a normal fluid state at high spin states, contributing to the concept of the atomic nucleus as a 'finite quantum many-body system'.
3.2. Activities at Major Academic Institutions
In 1953, Mottelson was appointed as a staff member in the Theoretical Study Group of CERN (European Organization for Nuclear Research), which was based in Copenhagen at the time. He held this position until 1957, when he became a professor at the newly established Nordic Institute for Theoretical Physics (Nordita) in Copenhagen. His academic engagements also included a visiting professorship at the University of California, Berkeley in the spring of 1959. In recognition of his long-standing contributions and residence in Denmark, Ben Roy Mottelson became a naturalized Danish citizen in 1971.
3.3. Scientific Contributions
Ben Roy Mottelson's fundamental contributions to nuclear physics revolutionized the understanding of the atomic nucleus. His work, primarily in collaboration with Aage Bohr, led to the development of the Bohr-Mottelson model, a pivotal theoretical framework. This model provided a unified description of the collective motion of nucleons within the nucleus and the independent particle motion, successfully integrating concepts from the liquid drop model and the shell model. Their research offered a theoretical explanation for the non-spherical geometry of atomic nuclei, a phenomenon that had previously been difficult to reconcile with simpler nuclear models. By demonstrating the connection between collective and particle motion, Mottelson and Bohr provided a comprehensive theory of nuclear structure that explained various nuclear properties, including their energy levels and charge distributions. Their insights extended to proposing the existence of a superfluid state within atomic nuclei and exploring phase transitions at high spin states, solidifying the concept of the nucleus as a complex 'finite quantum many-body system'.
4. Major Works and Awards
Throughout his distinguished career, Ben Roy Mottelson authored seminal works and received numerous prestigious awards and honors, recognizing his profound impact on nuclear physics.
4.1. Monograph "Nuclear Structure"
A significant scholarly achievement for Mottelson was the two-volume monograph titled Nuclear Structure, co-authored with Aage Bohr. The first volume, Single-Particle Motion, was published in 1969, followed by the second volume, Nuclear Deformations, in 1975. These comprehensive works became foundational texts in nuclear structure physics, widely regarded by the scientific community as a 'bible-like' textbook for their detailed and authoritative treatment of the subject.
4.2. Nobel Prize in Physics (1975)
In 1975, Ben Roy Mottelson was jointly awarded the Nobel Prize in Physics with his collaborators, Aage Bohr and James Rainwater. The Nobel Committee cited their collective achievement 'for the discovery of the connection between collective motion and particle motion in atomic nuclei and the development of the theory of the structure of the atomic nucleus based on this connection'. This recognition underscored the profound impact of their unified model in explaining the complex behavior and structure of atomic nuclei.
4.3. Other Awards and Honors
Beyond the Nobel Prize, Mottelson received several other significant accolades. In 1969, he was honored with the Atoms for Peace Award, which recognized his contributions to the peaceful uses of atomic energy. He was an honorary member of the Finnish Society of Sciences and Letters, a member of the American Philosophical Society, and a foreign fellow of both the Bangladesh Academy of Sciences and the Norwegian Academy of Science and Letters. From 1993 to 1997, he served as the director of the European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) in Trento, Italy.
5. Ideology and Social Activities
Ben Roy Mottelson's engagement extended beyond pure scientific inquiry, encompassing a thoughtful approach to his research and an active involvement in discussions concerning the broader societal implications of scientific advancements.
5.1. Scientific Philosophy and Research Approach
Mottelson's scientific philosophy was characterized by a deep commitment to understanding fundamental physical phenomena through rigorous theoretical modeling combined with empirical validation. His research approach was highly collaborative, exemplified by his long-standing partnership with Aage Bohr and his engagement with other leading physicists like James Rainwater and David Pines. He sought to unify disparate theoretical frameworks, such as the liquid drop and shell models, to create a more comprehensive description of the atomic nucleus. His work demonstrated an ability to draw analogies from other fields, like superconductivity, to provide novel insights into nuclear behavior, thus pioneering the concept of the atomic nucleus as a 'finite quantum many-body system'.
5.2. Engagement in Scientific and Social Circles
Mottelson was a prominent member of the board of sponsors of the Bulletin of the Atomic Scientists. This involvement highlights his concern for the societal implications of scientific discoveries, particularly in the realm of nuclear physics, and his commitment to promoting responsible scientific conduct and public discourse on issues related to atomic energy and global security.
6. Personal Life
Ben Roy Mottelson held dual citizenship, possessing both Danish and American passports. He resided in Copenhagen, Denmark, for the majority of his adult life. He was first married to Nancy Jane Reno in 1948. They had two sons and one daughter. Nancy Jane Reno passed away in 1975. Mottelson later married Britta Marger Siegumfeldt in 1983.
7. Death
Ben Roy Mottelson passed away on May 13, 2022, in Copenhagen, Denmark, at the age of 95.
8. Legacy and Impact
Ben Roy Mottelson's legacy is profound, marked by his transformative contributions to nuclear physics and his lasting influence on the scientific community.
8.1. Impact on Nuclear Physics
Mottelson's theoretical models, particularly the Bohr-Mottelson model and his work on the collective and particle motion within the atomic nucleus, fundamentally reshaped the understanding of nuclear structure. His research, including the concept of the nucleus as a 'finite quantum many-body system' and the exploration of superfluid states and phase transitions, stimulated extensive new theoretical and experimental studies. The two-volume monograph Nuclear Structure, co-authored with Aage Bohr, remains a cornerstone text, guiding and inspiring generations of physicists in the field.
8.2. Scientific Community's Evaluation
The scientific community has consistently recognized Mottelson's immense contributions. The joint award of the Nobel Prize in Physics in 1975 stands as the highest testament to the significance of his discoveries. Furthermore, the widespread adoption of his and Bohr's Nuclear Structure as a definitive textbook underscores the foundational and enduring nature of their work in nuclear structure physics.