Seth Neddermeyer

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Seth Neddermeyer
Seth Neddermeyer ID badge.png
ID badge photo from Los Alamos
Born Seth Henry Neddermeyer
(1907-09-16)September 16, 1907
Richmond, Michigan, U.S.
Died January 29, 1988(1988-01-29) (aged 80)
Seattle, Washington, U.S.
Fields Physics
Alma mater California Institute of Technology (Ph.D)
Doctoral advisor Carl David Anderson
Known for
Notable awards Enrico Fermi award (1982)

Seth Henry Neddermeyer (September 16, 1907 – January 29, 1988) was an American physicist who co-discovered the muon, and later championed the implosion-style plutonium atomic bomb at the Manhattan Project.[1]


Neddermeyer was Carl D. Anderson's Ph.D. student at Caltech. In 1936, he and Anderson discovered the muon, using cloud chamber measurements of cosmic rays.

Manhattan Project work[edit]

While at Los Alamos National Laboratory, Neddermeyer was an early advocate for the development of an implosion technique for assembling a critical mass in an atomic bomb. While implosion was suggested by Richard Tolman as early as 1942,[2] and discussed in the introductory lectures given to Los Alamos scientists by Robert Serber, Neddermeyer was one of the first to urge its full development. Unable to find much initial enthusiasm for the concept amongst his fellow Los Alamos scientists, Neddermeyer presented the first substantial technical analysis of implosion in late April 1943. Though many remained unimpressed, Robert Oppenheimer appointed Neddermeyer the head of a new group to test implosion.[3] Neddermeyer embarked on an intensive series of experiments testing cylindrical implosions.

Nevertheless, seemingly irresolvable problems with shock wave uniformity brought progress on implosion to a crawl. At the urging of James Conant, Oppenheimer brought in George Kistiakowsky (who had a specialized knowledge in the precision use of explosives) to help jumpstart the flagging program in January 1944.[4]

In April 1944 tests on the first sample of plutonium-239 that had been produced with neutrons in a nuclear reactor (rather than a cyclotron), revealed an unexpected problem: the reactor-bred plutonium contained five times more plutonium-240 (a result of reactor neutron bombardment), an unwanted isotope that spontaneously decayed and produced neutrons that promised to cause a pre-detonation, without sufficiently quick critical mass assembly. It now became apparent that only implosion would work for practical plutonium bombs, since neutrons from any amount of plutonium-240 which would be produced along with plutonium-239 in a workable reactor production scheme, would cause a pre-detonation in any gun-type bomb (see weapons grade plutonium for details). Plutonium-240, once produced in reactor-plutonium, was even more difficult to remove from plutonium-239 than isotopic separation of uranium. These facts made plutonium effectively unusable unless implosion worked. At the same time, it was becoming clear that only plutonium (rather than uranium) could be produced in quantities that would allow regular production (about one bomb core per month) of atomic bombs. Thus, the implosion technique now suddenly stood as the key to regular production of nuclear weapons.

In mid-June 1944 Kistiakowsky’s report to Oppenheimer about the dysfunctionality within the implosion team led to the ousting of Neddermeyer and his replacement by Kistiakowsky in order to get this essential operation working.[5] Neddermeyer was said to have been much embittered by this event. (Oppenheimer was also unhappy with this choice, but felt that no other possible course would allow timely development of practical bombs on a war schedule).

Accordingly, it was left to others like Kistiakowsky (who contributed a background in military ordnance and explosives), Robert Christy (who contributed the insight that a sub-critical sphere of plutonium could be imploded to a critical mass), John von Neumann (who contributed the breakthrough mathematical model for using shaped charges to create a truly spherical implosion), and Edward Teller (whose knowledge of the compressibility of metals led to the use of density change to achieve criticality rather than mere, same-density, “assembly”[6]), to complete the work. The implosion method championed by Neddermeyer was used in the first atom bomb exploded (Trinity test), the Fat Man bomb dropped on Nagasaki, and almost all modern weapons.

Later years[edit]

After World War II, Neddermeyer taught at the University of Washington until his death from complications of Parkinson's disease[7] in 1988.[8] In 1982, he was awarded with the Enrico Fermi award.


  1. ^ Geballe, Ronald; Lord, Jere J.; Streib, John F. (November 1988). "Seth N. Neddermeyer". Physics Today 41 (11): 109. Bibcode:1988PhT....41k.109G. doi:10.1063/1.2811634. 
  2. ^ Serber, Robert, The Los Alamos Primer: The First Lectures on How to Build an Atomic Bomb, pg 59, (University of California Press, 1992) ISBN 0-520-07576-5
  3. ^ Rhodes, Richard, The Making of the Atomic Bomb, Simon and Schuster, 1986, p. 466-67.
  4. ^ Rhodes, Richard, The Making of the Atomic Bomb, Simon and Schuster, 1986, p. 541-43.
  5. ^ Rhodes, Richard, The Making of the Atomic Bomb, Simon and Schuster, 1986, p. 547.
  6. ^ Serber, Robert, The Los Alamos Primer: The First Lectures on How to Build an Atomic Bomb, pg xvi, (University of California Press, 1992) ISBN 0-520-07576-5
  7. ^ "A-bomb scientist dies at age 80". The San Bernardino County Sun. 1 February 1988. p. 6. Retrieved 24 August 2014 – via  open access publication - free to read
  8. ^ "Seth Neddermeyer". Atomic Heritage Foundation. Retrieved 2014-01-26. 

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