Alastair G. W. Cameron

Cameron returned to Canada in 1954, taking a position at the Chalk River Laboratory operated by Atomic Energy of Canada Limited. There he hoped to apply advances from the rapidly developing field of nuclear physics to the field of astrophysics. In particular, he wished to calculate the nuclear cross sections involved in helium fusion reactions inside the cores of red giant stars, which could produce the neutrons necessary to produce the technetium observed by Merrill.[4] He quickly realized that traditional computational methods and slide rules were insufficient to calculate complex networks of nuclear reactions. He used of some of the first computers in Canada, originally purchased for use by the accounting department at the laboratory, to do the calculations.[3] At first, he was able to give programs on trays of punch cards to the accountants to run on his behalf. However, as his calculations increased in sophistication and the computing resources at Chalk River improved, he switched to work during the night and on weekends when the machines were not in use.[4][5]

In 1957, he published Nuclear Reactions in Stars and Nucleogenesis, known as the AGWC paper, which introduced an important, early, comprehensive theory of the production of chemical elements in stars, especially r-process elements. This work by Cameron, along with the B²FH paper (published in the same year by Margaret Burbidge, Geoffrey Burbidge, William A. Fowler, and Fred Hoyle), helped to publicise and direct research in the field of nuclear astrophysics.[6][8]

In 1959, after growing frustrated with what he saw as the Canadian government's lack of interest in investing in science, Cameron emigrated to the United States, which had just seen a major expansion of funding for space-science research due to the Sputnik crisis.[9][6] He held academic positions at the California Institute of Technology, the Goddard Institute for Space Studies, and at Yeshiva University. In 1973 he became a professor of astronomy at Harvard University and remained there for 26 years. From 1976 to 1982 he was chairman of the Space Science Board of the National Academy of Sciences.

Five days before his death in 2005, the 2006 Bethe Prize for his work on nuclear astrophysics was announced. Cameron would receive this award for his 50-year-old work on stellar nucleosynthesis, which was still an area of active research.

After learning about the 1960 discovery of an excess of xenon-129 due to the radioactive decay of iodine-129 in the Richardton meteorite, Cameron became interested in what the abundances of radioactive isotopes can tell us about the formation of the solar system and the interstellar medium. In 1975, he gave a seminar at Caltech, titled The Origin of the Solar System, where he outlined a unified model of the formation of the Solar System, from the Sun's formation from the collapse of cloud of gas and dust, the subsequent formation of a protoplanetary disk, to the formation of the gas giants and the terrestrial planets out of material from the disk. When an audience member asked, “What did you do on the seventh day?” he reportedly responded, “I rested.”[6]

Samples brought back from the Apollo program showed that the Moon was composed of the same material as the mantle of the Earth. This surprising result was still unexplained in the early 1970s, when Cameron began work on an explanation of the Moon's origins. He theorized that the formation of the Moon was the result of a tangential impact of an object at least the size of Mars on the early Earth.[10] In this model, the outer silicates of the body hitting the Earth would be vaporized, whereas a metallic core would not. The more volatile materials that were emitted during the collision would escape the Solar System, whereas silicates would tend to coalesce. Hence, most of the collisional material sent into orbit would consist of silicates, leaving the coalescing Moon deficient in iron and volatile materials, such as water.

After seeing William Hartmann present a similar, independent model at a conference in 1974, Cameron began a several decade-long collaboration with Hartmann to develop the giant-impact hypothesis.[1] Cameron was able to use increasingly sophisticated computer models to show that such a collision could produce an Earth-Moon system with the correct mass, spin, and orbital momentum.[2] The giant-impact theory gained mainstream acceptance as the scientific explanation for the origin of the Moon beginning in the 1980s.[1]

After his retirement from Harvard in 1999, Cameron held a position at the Lunar and Planetary Laboratory of the University of Arizona.[2]