Aage Bohr, who died on September 8 aged 87, was a pioneering nuclear physicist and Nobel Prize winner; in his youth he escaped from Nazi-occupied Denmark with his father, Niels Bohr, a central figure in the Manhattan Project, to whom Aage was a valuable assistant.
“I was born in Copenhagen on June 19, 1922, as the fourth son of Niels Bohr and Margrethe Bohr (née Nørlund). During my early childhood, my parents lived at the Institute for Theoretical Physics (now the Niels Bohr Institute), and the remarkable generation of scientists who came to join my father in his work became for us children Uncle Kramers, Uncle Klein, Uncle Nishina, Uncle Heisenberg, Uncle Pauli, etc.”
“When I was about ten years old, my parents moved to the mansion at Carlsberg, where they were hosts for widening circles of scholars, artists, and persons in public life.”
“I went to school for twelve years at Sortedam Gymnasium (H. Adler’s fæellesskole) and am indebted to many of my teachers, both in the humanities and in the sciences, for inspiration and encouragement.”
“I began studying physics at the University of Copenhagen in 1940 (a few months after the German occupation of Denmark). By that time, I had already begun to assist my father with correspondence, with his writing of articles of a general epistemological character, and gradually also in connection with his work in physics.”
“In those years, he was concerned partly with problems of nuclear physics and partly with problems relating to the penetration of atomic particles through matter.”
In October 1943, my father had to flee Denmark to avoid arrest by the Nazis, and the whole family managed to escape to Sweden, where we were warmly received. Shortly afterwards, my father proceeded to England, and I followed after him.
He became associated with the atomic energy project and, during the two years until we returned to Denmark, in August 1945, we travelled together spending extensive periods in London, Washington, and Los Alamos. I was acting as his assistant and secretary and had the opportunity daily to share in his work and thoughts.
We were members of the British team, and my official position was that of a junior scientific officer employed by the Department of Scientific and Industrial Research in London. In another context, I have attempted to describe some of the events of those years and my father’s efforts relating to the prospects raised by the atomic weapons
The Bohr family fled from Denmark to neutral Sweden in 1943 after Hitler had ordered the deportation of Danish Jews. From Sweden the Bohrs headed for London where Niels became involved in what Aage was later to call, somewhat euphemistically, “the atomic energy project”.
In fact the Manhattan Project was a race against the Nazis to build the first atom bomb. Niels Bohr’s expertise was crucial to the Allies, and Aage, by then officially a “junior scientific officer employed by the Department of Scientific and Industrial Research” became a laboratory assistant to his father at the Manhattan Project’s headquarters in Los Alamos, New Mexico.
As the extraordinarily devastating power of the atom bomb became clear, however, both men cautioned against using it, and voiced their concerns to British and American leaders. In the end, the bombs that were dropped on Hiroshima and Nagasaki were credited with bringing the war to a speedy end.
In September 1943 Hitler demanded the deportation of Denmark’s more than 7,000 Jews. Within days the community was being smuggled in huge numbers across the narrow Oresund channel to the sanctuary of Sweden. Having established his family in safety, Niels Bohr soon left for London and the Manhattan Project, where he was quickly joined by Aage. They were not to return to Denmark until August 1945.
On their return, Aage Bohr began to craft a reputation as a profoundly gifted physicist in his own right. He resumed his studies at Copenhagen University, and, two years after completing his Masters degree in 1946, he left for America to pursue his research at the Institute of Advanced Study at Princeton. In 1949 he teamed up with the American physicist James Rainwater to study the architecture at the heart, or nucleus, of atoms.
Their work led Bohr to challenge the conclusions of his own father, who had established one of the two theories about nuclear structure then vying for acceptance. Niels Bohr had suggested that protons and neutrons within an atom’s nucleus are held together in the same manner by which molecules are attracted to each other in a drop of liquid.
James Rainwater showed that neither Niels Bohr, nor his rival Maria Goeppert-Mayer, who proposed that protons and neutrons were held in orbits within the nucleus, had fully explained nuclear structure. To explain the inconsistencies in their theories, he suggested that some nuclei were not perfectly round.
Aage Bohr returned to Copenhagen in 1950, determined to resolve the issue. He struck up a collaboration with another American physicist, Ben Mottelson. Bohr felt they were “kindred spirits” and it was a fruitful partnership. Within two years the pair had published their “collective model” of nuclear structure. It combined the two existing theories, noting that, as Rainwater had predicted, centrifugal forces distorted some spherical nuclei into an oval shape.
The men were to refine their study of nuclear structure over the next 25 years, publishing their conclusions in two volumes (1969 and 1975). It was for this work, fundamentally reappraising the central building blocks of atoms, that Bohr, Mottelson and Rainwater were collectively awarded the Nobel Prize in 1975.
By that time Bohr had been head of the Niels Bohr Institute for 12 years, taking over after his father’s death in 1962. He left the Institute in 1967 to dedicate himself to his research.
After winning the Nobel Prize, Bohr ran the Nordic Institute for Theoretical Nuclear Physics, which his father had set up in 1957 to encourage theoretical physics, notably in the fields of astrophysics, condensed matter physics, and subatomic physics.
By the time of his retirement in 1981, Aage Bohr had won many awards, including the Pope Pius XI Medal (1963) and the Ole Romer Medal (1976). He was a member of many scientific academies in Europe and the National Academy of Science in the United States.
Aage Bohr, who enjoyed classical music and himself played the piano, married in 1950, Marietta Soffer, with whom he had two sons and a daughter. After she died, he married, in 1981, Bente Meyer Scharff, who survives him.