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 astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
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 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 749,6 ...
, 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
A Bachelor of Science (BS, BSc, SB, or ScB; from the Latin ') is a bachelor's degree awarded for programs that generally last three to five years.
The first university to admit a student to the degree of Bachelor of Science was the University of ...
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
Chalk River Laboratories (french: Laboratoires de Chalk River; also known as CRL, Chalk River Labs and formerly Chalk River Nuclear Laboratories, CRNL) is a Canadian nuclear research facility in Deep River, about north-west of Ottawa.
CRL is ...](_blank)
, 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, t ...
. 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 vacu ...
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 H ...
. 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 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 technetium is a spontaneous ...
in the variable star
R Andromedae
R Andromedae (R And) is a Mira-type variable star in the constellation Andromeda. Its spectral class is type S because it shows absorption bands of zirconium monoxide (ZrO) in its spectrum. It was among the stars found by Paul Merrill ...
and other red variable stars by the American astronomer
Paul Merrill. 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 beh ...
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
Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work ...
'', 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 thi ...
. 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. ...
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 is ...
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 (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
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 Fellow of the Royal Society, FRS (24 September 1925 – 26 January 2010) was an English people, English astronomy professor and theoretical astrophysicist, most recently at the University of California, San Diego. He wa ...
,
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 wit ...
, 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
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 ...
.
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 Universit ...
. In 1973 he became a professor of astronomy at
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 ...
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 Nati ...
.
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 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 orient ...
, Cameron became interested in what the abundances of radioactive isotopes can tell us about the formation of the
solar system
The Solar SystemCapitalization 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 S ...
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 interstella ...
. 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, Ve ...
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 (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
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 surfa ...
. 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.
T ...
.
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
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 Nati ...
* 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
Sour ...
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 act ...
* 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 The Henry Norris Russell Lectureship is awarded each year by the American Astronomical Society in recognition of a lifetime of excellence in astronomical research. The idea for the lectureship came from then society President Harlow Shapley in 1945, ...
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.
See also
*
2980 Cameron
References
External links
Oral history interview transcript for Alastair G. W. Cameron on 10 February 2003, American Institute of Physics, Niels Bohr Library & ArchivesLaudatio from the Bethe PrizeDavid 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