Alastair G. W. (Graham Walter) Cameron (21 June 1925 – 3 October 2005) was an American-Canadian astrophysicist and space scientist who was an eminent staff member of the

Astronomy Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galax ...

department of

Harvard University Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher le ...

. He was one of the founders of the field of

nuclear astrophysics Nuclear astrophysics is an interdisciplinary part of both nuclear physics and astrophysics, involving close collaboration among researchers in various subfields of each of these fields. This includes, notably, nuclear reactions and their rates as ...

, advanced the theory that the Moon was created by the

giant impact The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact, suggests that the Moon formed from the ejecta of a collision between the proto-Earth and a Mars-sized planet, approximately 4.5 billion years ago, in the Hadean ...

of a Mars-sized object with the early Earth, and was an early adopter of computer technology in astrophysics.

Early life and education

Alastair Cameron was born in

Winnipeg Winnipeg () is the capital and largest city of the province of Manitoba in Canada. It is centred on the confluence of the Red and Assiniboine rivers, near the longitudinal centre of North America. , Winnipeg had a city population of 749,60 ...

, Manitoba, to parents of Scottish descent. His father, born in

London, England London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a major s ...

, was chemist A.T. Cameron, a professor and chair of the biochemistry department at Manitoba Medical College. 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." In 1940 (When Cameron was only 15 years old), he made a bet with a high school classmate that man would land on the

moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

within 40 years. When the Apollo 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. Cameron earned a Bachelor of Science degree from the

University of Manitoba The University of Manitoba (U of M, UManitoba, or UM) is a Canadian public research university in the province of Manitoba.Chalk River Laboratory, a Canadian research facility on

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...

. He went on to do graduate work in both theoretical and experimental nuclear physics at the

University of Saskatchewan A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States, the ...

. Under the supervision of Leon Katz, he studied photonuclear cross sections using the university's new 25

MeV In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. ...

betatron A betatron is a type of cyclic particle accelerator. It is essentially a transformer with a torus-shaped vacuum tube as its secondary coil. An alternating current in the primary coils accelerates electrons in the vacuum around a circular path. Th ...

accelerator. In 1952, earned the first PhD awarded in physics from the university.

Career

After finishing his PhD, he spent two years as an assistant professor at the

Iowa State College Iowa State University of Science and Technology (Iowa State University, Iowa State, or ISU) is a public land-grant research university in Ames, Iowa. Founded in 1858 as the Iowa Agricultural College and Model Farm, Iowa State became one of the n ...

and worked at the

Ames Laboratory Ames National Laboratory, formerly Ames Laboratory, is a United States Department of Energy national laboratory located in Ames, Iowa, and affiliated with Iowa State University. It is a top-level national laboratory for research on national sec ...

at the university, which was run by the

United States Atomic Energy Commission The United States Atomic Energy Commission (AEC) was an agency of the United States government established after World War II by U.S. Congress to foster and control the peacetime development of atomic science and technology. President ...

. There he taught nuclear physics and helped to increase the electron beam current in the facility's new 70-MeV

synchrotron A synchrotron is a particular type of cyclic particle accelerator, descended from the cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The magnetic field which bends the particle beam into its closed p ...

particle accelerator. While at the Ames lab, he read an article in ''Science News Letter'' magazine (now ''Science News''), about the detection of the element

technetium Technetium is a chemical element with the Symbol (chemistry), symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive. All available technetium is produced as a synthetic element. Naturally occurring techneti ...

in the variable star R Andromedae and other red variable stars by the American astronomer

Paul Merrill Paul Willard Merrill (August 15, 1887 – July 19, 1961) was an American astronomer whose specialty was spectroscopy. He was the first to define S-type stars in 1922. Career He received his Ph.D. at the University of California (now UC Berkeley ...

. Since this element has no stable isotopes, the observed technetium would experience radioactive decay with

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

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 with

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

s. Excited by this clue to the astrophysical origins of

heavy elements upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...

, Cameron decided to switch fields study astrophysics. Having never taken an astronomy class, he purchased several graduate-level textbooks, subscribed to ''

the Astrophysical Journal ''The Astrophysical Journal'', often abbreviated ''ApJ'' (pronounced "ap jay") in references and speech, is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and Jame ...

'', and began an intense period of self-study.

Stellar nucleosynthesis

Cameron returned to Canada in 1954, taking a position at the Chalk River Laboratory operated by

Atomic Energy of Canada Limited Atomic Energy of Canada Limited (AECL) is a Canadian federal Crown corporation and Canada's largest nuclear science and technology laboratory. AECL developed the CANDU reactor technology starting in the 1950s, and in October 2011 licensed this ...

. 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 section The nuclear cross section of a nucleus is used to describe the probability that a nuclear reaction will occur. The concept of a nuclear cross section can be quantified physically in terms of "characteristic area" where a larger area means a larger ...

s involved in

helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. It ...

fusion Fusion, or synthesis, is the process of combining two or more distinct entities into a new whole. Fusion may also refer to: Science and technology Physics *Nuclear fusion, multiple atomic nuclei combining to form one or more different atomic nucl ...

reactions inside the cores of red giant stars, which could produce the neutrons necessary to produce the technetium observed by Merrill. He quickly realized that traditional computational methods and

slide rule The slide rule is a mechanical analog computer which is used primarily for multiplication and division, and for functions such as exponents, roots, logarithms, and trigonometry. It is not typically designed for addition or subtraction, which i ...

s 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. 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. 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 element A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...

s in

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth ma ...

s, especially

r-process In nuclear astrophysics, the rapid neutron-capture process, also known as the ''r''-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", ...

elements. This work by Cameron, along with the B²FH paper (published in the same year by

Margaret Burbidge Eleanor Margaret Burbidge, FRS (; 12 August 1919 – 5 April 2020) was a British-American observational astronomer and astrophysicist. In the 1950s, she was one of the founders of stellar nucleosynthesis and was first author of the influentia ...

Geoffrey Burbidge Geoffrey Ronald Burbidge FRS (24 September 1925 – 26 January 2010) was an English astronomy professor and theoretical astrophysicist, most recently at the University of California, San Diego. He was married to astrophysicist Margaret Burbi ...

William A. Fowler William Alfred Fowler ( ) was an American nuclear physicist, later astrophysicist, who, with Subrahmanyan Chandrasekhar, won the 1983 Nobel Prize in Physics. He is known for his theoretical and experimental research into nuclear reactions with ...

, and

Fred Hoyle Sir Fred Hoyle FRS (24 June 1915 – 20 August 2001) was an English astronomer who formulated the theory of stellar nucleosynthesis and was one of the authors of the influential B2FH paper. He also held controversial stances on other sci ...

), helped to publicise and direct research in the field of

. 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 The Sputnik crisis was a period of public fear and anxiety in Western nations about the perceived technological gap between the United States and Soviet Union caused by the Soviets' launch of ''Sputnik 1'', the world's first artificial satelli ...

. He held academic positions at the

California Institute of Technology The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

, the

Goddard Institute for Space Studies The Goddard Institute for Space Studies (GISS) is a laboratory in the Earth Sciences Division of NASA's Goddard Space Flight Center affiliated with the Columbia University Earth Institute. The institute is located at Columbia University in Ne ...

, and at

Yeshiva University Yeshiva University is a private Orthodox Jewish university with four campuses in New York City."About YU
on the Yeshiva Universi ...

. In 1973 he became a professor of astronomy at

and remained there for 26 years. From 1976 to 1982 he was chairman of the Space Science Board of the

National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Natio ...

. 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.

Formation of the Solar System

After learning about the 1960 discovery of an excess of

xenon-129 Naturally occurring xenon (54Xe) consists of seven stable isotope, stable isotopes and two very long-lived isotopes. Double electron capture has been observed in 124Xe (half-life ) and double beta decay in 136Xe (half-life ), which are among the l ...

due to the radioactive decay of

iodine-129 Iodine-129 (129I) is a long-lived radioisotope of iodine which occurs naturally, but also is of special interest in the monitoring and effects of man-made nuclear fission products, where it serves as both tracer and potential radiological contami ...

in the

Richardton meteorite The Richardton meteorite is a H5 Ordinary chondrite that was seen to fall at 21:48 on 30 June 1918 between Mott, North Dakota and Richardton, North Dakota, United States. Pieces were found in a strewn field of about by centred on and oriente ...

, Cameron became interested in what the abundances of radioactive isotopes can tell us about the formation of the

solar system The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

and the

interstellar medium In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstellar ...

. In 1975, he gave a seminar at

Caltech The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

, 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 A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...

, to the formation of the

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...

s and the

terrestrial planet A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, ...

s out of material from the disk. When an audience member asked, “What did you do on the seventh day?” he reportedly responded, “I rested.”

Formation of the Moon

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 Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmosp ...

on the early

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surface ...

. 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 The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact, suggests that the Moon formed from the ejecta of a collision between the proto-Earth and a Mars-sized planet, approximately 4.5 billion years ago, in the Hadean ...

. 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. The giant-impact theory gained mainstream acceptance as the scientific explanation for the origin of the Moon beginning in the 1980s. After his retirement from Harvard in 1999, Cameron held a position at the

Lunar and Planetary Laboratory The Lunar and Planetary Laboratory (LPL) is a research center for planetary science located in Tucson, Arizona. It is also a graduate school, constituting the Department of Planetary Sciences at the University of Arizona. LPL is one of the wo ...

of the

University of Arizona The University of Arizona (Arizona, U of A, UArizona, or UA) is a public land-grant research university in Tucson, Arizona. Founded in 1885 by the 13th Arizona Territorial Legislature, it was the first university in the Arizona Territory. Th ...

Awards and recognition

* 1961 Fellow of the

Royal Society of Canada The Royal Society of Canada (RSC; french: Société royale du Canada, SRC), also known as the Academies of Arts, Humanities and Sciences of Canada (French: ''Académies des arts, des lettres et des sciences du Canada''), is the senior national, bil ...

*1970 R.M. Petrie Prize Lecture Award of the Canadian Astronomical Society *1972 Fellow of the

American Physical Society The American Physical Society (APS) is a not-for-profit membership organization of professionals in physics and related disciplines, comprising nearly fifty divisions, sections, and other units. Its mission is the advancement and diffusion of k ...

*1976 Member of the

* 1983 NASA Distinguished Public Service Medal * 1988

J. Lawrence Smith Medal J. Lawrence Smith Medal is awarded every three years by the National Academy of Sciences for investigations of meteoric bodies. The medal is in honor of its namesake, the American chemist and meteoriticist, J. Lawrence Smith. Recipients Sourc ...

of the National Academy of Sciences * 1989 Harry H. Hess Medal of the

American Geophysical Union The American Geophysical Union (AGU) is a 501(c)(3) nonprofit organization of Earth, atmospheric, ocean, hydrologic, space, and planetary scientists and enthusiasts that according to their website includes 130,000 people (not members). AGU's ...

* 1994

Leonard Medal The Leonard Medal honors outstanding contributions to the science of meteoritics and closely allied fields. It is awarded by the Meteoritical Society. It was established in 1962 to honor the first President of the Society, Frederick C. Leonard. ...

of the

Meteoritical Society The Meteoritical Society is a non-profit scholarly organization founded in 1933 to promote research and education in planetary science with emphasis on studies of meteorites and other extraterrestrial materials that further our understanding of the ...

* 1997 Henry Norris Russell Lectureship of the

American Astronomical Society The American Astronomical Society (AAS, sometimes spoken as "double-A-S") is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the adv ...

* 2006

Hans Bethe Prize The Hans A. Bethe Prize, is presented annually by the American Physical Society. The prize honors outstanding work in theory, experiment or observation in the areas of astrophysics, nuclear physics, nuclear astrophysics, or closely related fields ...

Personal life

Cameron married Elizabeth MacMillan in 1955. She died in 2001. 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. Cameron died on October 3, 2005, from heart failure. He was 80 years old.

References

External links

Oral history interview transcript for Alastair G. W. Cameron on 10 February 2003, American Institute of Physics, Niels Bohr Library & Archives

Laudatio from the Bethe Prize

David Arnett, "A. G. W. Cameron", Biographical Memoirs of the National Academy of Sciences (2017)
{{DEFAULTSORT:Cameron, Alastair G.W. Canadian physicists 1925 births 2005 deaths 20th-century Canadian astronomers Members of the United States National Academy of Sciences People from Winnipeg Harvard University faculty University of Manitoba alumni University of Saskatchewan alumni Fellows of the American Physical Society