Herbert G. MacPherson (2 November 1911 – 6 January 1993) was an American nuclear engineer and deputy director of

Oak Ridge National Laboratory Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research and ...

(ORNL). He contributed to the design and development of nuclear reactors and in the opinion of

Alvin Weinberg Alvin Martin Weinberg (; April 20, 1915 – October 18, 2006) was an American nuclear physicist who was the administrator at Oak Ridge National Laboratory (ORNL) during and after the Manhattan Project. He came to Oak Ridge, Tennessee, in 1945 ...

he was "the country's foremost expert on graphite"...

Career

After receiving his Ph.D. in Physics from the University of California at Berkeley in 1936, MacPherson went to work at the National Weather Service in Washington DC. The following year he was hired by the National Carbon Division of the

Union Carbide Union Carbide Corporation is an American chemical corporation wholly owned subsidiary (since February 6, 2001) by Dow Chemical Company. Union Carbide produces chemicals and polymers that undergo one or more further conversions by customers befor ...

and Carbon Corporation in Cleveland Ohio, where he investigated the spectra of carbon arcs that were often used in the movie industry. In 1956 he moved to Oak Ridge TN to become a research scientist at the Oak Ridge National Laboratory. MacPherson became deputy director of Oak Ridge National Laboratory in 1965, a position he held until 1970. From 1970 to 1976 he held the position of Professor of Nuclear Engineering at the University of Tennessee. In 1973 he served as acting director of the Institute for Energy Analysis, an organization founded by

for the study of management and future sources of energy. In 1978 he was elected to membership in the National Academy of Engineering.

Nuclear graphite and the
Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...

The possibility of creating a chain reaction in

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...

became apparent in 1939 following the

nuclear fission Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radio ...

experiments of Otto Hahn and

Fritz Strassman Friedrich Wilhelm Strassmann (; 22 February 1902 – 22 April 1980) was a German chemist who, with Otto Hahn in December 1938, identified the element barium as a product of the bombardment of uranium with neutrons. Their observation was the k ...

, and the interpretation of these results by

Lise Meitner Elise Meitner ( , ; 7 November 1878 – 27 October 1968) was an Austrian-Swedish physicist who was one of those responsible for the discovery of the element protactinium and nuclear fission. While working at the Kaiser Wilhelm Institute on rad ...

and

Otto Frisch Otto Robert Frisch FRS (1 October 1904 – 22 September 1979) was an Austrian-born British physicist who worked on nuclear physics. With Lise Meitner he advanced the first theoretical explanation of nuclear fission (coining the term) and first ...

. The exciting possibilities that this presented rapidly spread throughout the world physics community. In order for the fission process to chain react, the neutrons created by uranium fission must be slowed down by interacting with a

neutron moderator In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, ideally without capturing any, leaving them as thermal neutrons with only minimal (thermal) kinetic energy. These thermal neutrons are immensely mo ...

(an element with a low atomic weight, that will "bounce", when hit by a neutron) before they will be captured by other uranium atoms. It was well known in 1939 that the two most promising moderators were heavy water and

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large ...

(a semi-crystalline form of pure carbon). In February 1940, using funds that were allocated partly as a result of the Einstein-Szilard letter to President Roosevelt, Leo Szilard purchased 4 tons of graphite from National Carbon for use in

Enrico Fermi Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1. He has been called the "architect of the nuclear age" and ...

's experimental reactor, the so-called exponential pile. Fermi writes that "The results of this experiment was icsomewhat discouraging" presumably due to the absorption of neutrons by some unknown impurity. So, in December 1940 Fermi and Szilard met with H. G. MacPherson and V. C. Hamister at National Carbon to discuss the possible existence of impurities in graphite, without specifically describing the reasons for their visit. Having previously (September 1939) read the article of R. B. Roberts and J. B. H. Kuper (which described the necessity of a moderator in a chain reaction), MacPherson was able to deduce the purpose of the visit. Because of his experience with the spectra of carbon arcs he realized that even high quality graphite contains minute quantities of

boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...

impurities that could make it potentially unusable as a neutron moderator in a uranium reactor, confirming a suspicion of Szilard. As a result of this meeting, over the next two years, MacPherson (together with L. M. Currie and V. C. Hamister) developed thermal purification techniques for the production of low boron content graphite, which resulted in the product "AGOT Graphite" of National Carbon. According to W. P. Eatherly, it was "the first true nuclear grade graphite". By November 1942, National Carbon had shipped 250 tons of AGOT graphite to the University of Chicago where it was used in the construction of Fermi's

Chicago Pile-1 Chicago Pile-1 (CP-1) was the world's first artificial nuclear reactor. On 2 December 1942, the first human-made self-sustaining nuclear chain reaction was initiated in CP-1, during an experiment led by Enrico Fermi. The secret development of t ...

, the first nuclear reactor to generate a sustained chain reaction. AGOT graphite was also used to build the X-10 graphite reactor in Oak Ridge TN and the reactors at the Hanford Site in Washington, which produced plutonium during and after World War II. This process and its later refinements became standard techniques in the manufacture of nuclear graphite. This crucial information concerning boron impurities was not known to the German scientists who attempted to create a chain reaction in uranium during the second world war. The cross section for neutron absorption in graphite was investigated in Germany by Walter Bothe, P. Jensen, and

Werner Heisenberg Werner Karl Heisenberg () (5 December 1901 – 1 February 1976) was a German theoretical physicist and one of the main pioneers of the theory of quantum mechanics. He published his work in 1925 in a breakthrough paper. In the subsequent series ...

who found it to be too high, thereby eliminating graphite as a possible moderator. Consequently, the German effort to create a chain reaction involved attempts to use heavy water, an expensive and scarce alternative. Writing as late as 1947, Heisenberg still did not understand that the only problem with graphite was the boron impurities.

Molten Salt Reactor

In 1956 MacPherson was appointed by ORNL director

, to lead the Molten Salt Reactor Experiment, a revolutionary safe, efficient and relatively inexpensive reactor design, now referred to as the

Thorium fuel cycle The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural tho ...

. Within two years the chemical tests of molten materials, cost studies, overall design, and calculations had been completed and were outlined in MacPherson's quarterly progress report on the MSRE. Computations were performed on the

ORACLE (computer) The ORACLE or ''Oak Ridge Automatic Computer and Logical Engine'', an early computer built by Oak Ridge National Laboratory, was based on the IAS architecture developed by John von Neumann. Summary The ''Oak Ridge National Laboratory Review'' ...

, a clone of von Neumann's IAS machine that had been built at ORNL under the guidance of

Alston Scott Householder Alston Scott Householder (5 May 1904 – 4 July 1993) was an American mathematician who specialized in mathematical biology and numerical analysis. He is the inventor of the Householder transformation and of Householder's method. Career Househ ...

. The MSRE was funded by the Atomic Energy Commission in 1959 and was completed in 1965. It ran continuously until it was shut down in 1969, but it had proved the viability of the design Weinberg refers to this project as "perhaps the most ingenious and daring engineering experiment ever conducted at ORNL". (In 1972 the U.S. government declined to fund the proposed follow-up molten salt breeder reactor at ORNL, fired Alvin Weinberg, and redirected its support towards the design and construction of liquid metal fast breeder reactors, such as the

Clinch River Breeder Reactor The Clinch River Nuclear Site (CRNS) is a project site owned by the Tennessee Valley Authority (TVA). It was once proposed as the Clinch River Breeder Reactor Project of the U.S. Atomic Energy Commission (and a successor agency, the U.S. Energy R ...

.) In 1958, concurrently with the publication of the first textbook on nuclear reactors, MacPherson (together with James Lane and Frank Maslan) edited and published their engineering treatise on fluid fuel reactors

Mayan Archaeology

After he retired, MacPherson developed an interest in Mayan culture and writings, especially those pertaining to the

Dresden Codex The ''Dresden Codex'' is a Maya civilization, Maya book, which was believed to be the oldest surviving book written in the Americas, dating to the 11th or 12th century. However, in September 2018 it was proven that the Maya Codex of Mexico, pre ...

. This ancient Mayan manuscript contains a table, commonly referred to as the "Eclipse Warning Table" of dates, the intervals between which approximately correspond to the intervals between solar eclipses that occur worldwide. Hundreds of articles have been written in attempts to understand this table (see). MacPherson studied the baffling problem of how an ancient civilization may have succeeded in generating such a table when it did not possess the astronomical models that would be needed to predict eclipses worldwide and when only several solar eclipses would have been visible to the Maya throughout the whole period of their civilization. In what some experts consider to be "the most interesting of the recent studies of the eclipse table",MacPherson described a simple procedure by which such a table may have been assembled by Mayan astronomers in the process of determining the "lunar season".

References

External links