Alastair G. W. Cameron | |
|---|---|
 | |
| Born | (1925-06-21)21 June 1925 |
| Died | 3 October 2005(2005-10-03) (aged 80) |
| Citizenship | Canadian, American |
| Alma mater | University of Manitoba, University of Saskatchewan |
| Known for | r-process,stellar nucleosynthesis |
| Awards | Petrie Prize Lecture (1970) Hans Bethe Prize (2006) |
| Scientific career | |
| Institutions | Caltech, Goddard Institute for Space Studies, Yeshiva University, Harvard University |
| Doctoral advisor | Leon Katz |
Alastair Graham Walter Cameron (21 June 1925 – 3 October 2005)[1] was an American–Canadianastrophysicist and space scientist who was an eminent staff member of theAstronomy department ofHarvard University. He was one of the founders of the field ofnuclear astrophysics, advanced the theory that the Moon was created by thegiant impact of a Mars-sized object with the early Earth, and was an early adopter of computer technology in astrophysics.
Alastair Cameron was born inWinnipeg, Manitoba, to parents of Scottish descent. His father, born inLondon, England, was chemist A.T. Cameron, a professor and chair of the biochemistry department atManitoba Medical College.[2][3] He recalls addressing all men as “Doctor” as a four-year-old, noting it was "clearly an early attempt at forming a hypothesis based on limited data."[4]
In 1940 (When Cameron was only 15 years old), he made a bet with a high school classmate that man would land on theMoon within 40 years. When theApollo program achieved a successful Moon landing in 1969, the former classmate sent a cheque to settle the bet, which Cameron had framed and hung on the wall in his office.[3][2]
Cameron earned aBachelor of Science degree from theUniversity of Manitoba in Physics and Mathematics. During the summers, he worked at theChalk River Laboratory, a Canadian research facility onOntario.[5] He went on to do graduate work in both theoretical and experimental nuclear physics at theUniversity of Saskatchewan. Under the supervision ofLeon Katz, he studiedphotonuclearcross sections using the university's new 25MeVbetatron accelerator. In 1952, earned the first PhD awarded in physics from the university.[6][7]
After finishing his PhD, he spent two years as an assistant professor at theIowa State College and worked at theAmes Laboratory at the university, which was run by theUnited States Atomic Energy Commission. There he taught nuclear physics and helped to increase the electron beam current in the facility's new 70-MeVsynchrotron particle accelerator.[4][5]
While at the Ames lab, he read an article inScience News Letter magazine (nowScience News), about the detection of the elementtechnetium in the variable starR Andromedae and other red variable stars by the American astronomerPaul Merrill. Since this element has no stable isotopes, the observed technetium would experience radioactive decay withhalf-life of about 200,000 years, which was much shorter than the lifetime of the star. Cameron realized that this meant the technetium must have formed inside the stars where it was observed, by bombarding other elements withneutrons. Excited by this clue to the astrophysical origins ofheavy elements, Cameron decided to switch fields study astrophysics.[5][3] Having never taken an astronomy class, he purchased several graduate-level textbooks, subscribed tothe Astrophysical Journal, and began an intense period of self-study.[3][4]
Cameron returned to Canada in 1954, taking a position at the Chalk River Laboratory operated byAtomic 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 thenuclear cross sections involved inheliumfusion reactions inside the cores ofred giant stars, which could produce the neutrons necessary to produce the technetium observed by Merrill.[4] He quickly realized that traditional computational methods andslide 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 publishedNuclear Reactions in Stars and Nucleogenesis, known as the AGWC paper, which introduced an important, early, comprehensive theory of the production ofchemical elements instars, especiallyr-process elements. This work by Cameron, along with theB2FH paper (published in the same year byMargaret Burbidge,Geoffrey Burbidge,William A. Fowler, andFred Hoyle), helped to publicise and direct research in the field ofnuclear 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 theSputnik crisis.[9][6] He held academic positions at theCalifornia Institute of Technology, theGoddard Institute for Space Studies, and atYeshiva University. In 1973 he became a professor of astronomy atHarvard University and remained there for 26 years. From 1976 to 1982 he was chairman of the Space Science Board of theNational 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 ofxenon-129 due to the radioactive decay ofiodine-129 in theRichardton meteorite, Cameron became interested in what the abundances of radioactive isotopes can tell us about the formation of theSolar System and theinterstellar medium. In 1975, he gave a seminar atCaltech, titledThe 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 aprotoplanetary disk, to the formation of thegas giants and theterrestrial 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 theApollo 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 ofMars on the earlyEarth.[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 seeingWilliam Hartmann present a similar, independent model at a conference in 1974, Cameron began a several decade-long collaboration with Hartmann to develop thegiant-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 theLunar and Planetary Laboratory of theUniversity of Arizona.[2]
Cameron married Elizabeth MacMillan in 1955.[2] She died in 2001.[1]
While Cameron became a naturalized United States citizen in 1963 in order to receive the security clearances necessary to work in the US space program, he frequently returned to visit his native Canada and remained active in Canadian politics throughout his life.[17][3]
Cameron died on October 3, 2005,[18] from heart failure. He was 80 years old.
