Julius Ashkin

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Julius Ashkin
Julius Ashkin Los Alamos ID.png
Julius Askin's Los Alamos ID badge
Born (1920-08-23)August 23, 1920
Brooklyn, New York
Died June 4, 1982(1982-06-04) (aged 61)
Bronx, New York
Citizenship United States
Fields Physics
Institutions Metallurgical Laboratory
Los Alamos Laboratory
University of Rochester
Carnegie Mellon University
Alma mater Columbia University
Thesis Two problems in the statistical mechanics of crystals. I. The propagation of order in crystal lattices II. The statistics of two-dimensional lattices with four components.[1] (1943)
Doctoral advisor Willis Lamb

Julius Ashkin (August 23, 1920 – June 4, 1982) was a leader in experimental and theoretical physics known for furthering the evolution of particle physics from nuclear physics. As a theoretical physicist he made contributions in the fields of statistical mechanics, solid state physics, nuclear physics, and elementary particle physics. As an experimental physicist his main contributions concerned the passage of certain particles (pi-mesons, or pions) through solid matter and their subsequent decay. He was recognized for the quality of his research and teaching.

Early life[edit]

Julius Ashkin was born in Brooklyn, New York,[2] on August 23, 1920. His parents were Isadore and Anna Ashkin. He had two younger siblings, a brother, Arthur, also a physicist, and a sister, Ruth. One older sibling, Gertrude, died while young. The family home was in Brooklyn, New York, at 983 E 27 Street. Isadore had immigrated to the United States from Odessa, Russia at the age of 19. Anna, five years younger, also came from the Ukraine (in her case Galicia).[3][4][5][6] Within a decade of his landing in New York, Isadore had become a U.S. citizen and was running a dental laboratory at 139 Delancey Street in Manhattan.[7][8]


Ashkin attended Brooklyn's James Madison High School, graduating in 1936, while still a few weeks shy of his 16th birthday. In his senior year, he received honors and awards.[9] He was awarded a scholarship to attend Columbia University,[10][11] where he studied four years as an undergraduate from 1936 to 1940, and three as a graduate from 1940 to 1943.[12]

Physicists then working on Columbia's faculty in those years included professors Enrico Fermi, Isidor Isaac Rabi, Hans Bethe (visiting), Edward Teller (visiting), and instructors Arnold Nordsieck, Hugh Paxton,[13] and Willis Lamb. All these men were recognized as among the finest of their generation and four of them — Fermi, Rabi, Bethe, and Lamb — were to be awarded the Nobel Prize.[7][14]

As an undergraduate, Ashkin was invited to join an honorary mathematics society,[15] and received awards.[7][16][17][18] He entered the fall semester as an assistant lecturer and began work toward a master's degree. A year later, having received that degree, he began work toward a Ph.D. under the supervision of Willis Lamb. As a graduate student, Ashkin contributed to one paper in astrophysics.[19] and two papers in statistical mechanics[20][21][22][23][24] He collaborated with Lamb in writing the first of the two papers on statistical mechanics and with Teller in writing the second. This second paper, "Statistics of Two-Dimensional Lattices with Four Components"[21][21][24][25][26] has since been frequently cited.[27] He received his Ph.D. in Physics in 1943.[28][29]

Manhattan Project[edit]

Early stages of the Manhattan Project at Columbia University[edit]

During the latter part of 1942, before completing his Ph.D. work, Ashkin accepted an offer to work in the Manhattan Project. Early work on the development of the atom bomb had taken place at Columbia during the six years Ashkin was an undergradutate and graduate student there. When the process of nuclear fission was discovered in 1938, scientists in many locations in Europe and the United States began intense work to understand and control the phenomenon. Researchers at Columbia and nearby Princeton University were in the forefront of this work. There's no information on how much, if at all, Ashkin was involved in the effort at this early stage of his career, but it is certain that the Columbia physics department was the workplace for scientists who were devoted to the secret development of a new and phenomenally powerful weapon. These men included men already mentioned — Fermi, Rabi, Teller, and Bethe — as well as Leó Szilárd (who worked with Fermi to demonstrate that a nuclear reaction was possible), Herbert L. Anderson (then, like Ashkin, a Columbia graduate student), John R. Dunning (an associate professor at Columbia who had built a small cyclotron in the mid-1930s), Walter Zinn (a Columbia professor who worked with the Columbia cyclotron to demonstrate the possibility of a sustained chain reaction), George B. Pegram (Dean of Columbia's Faculties of Political Science, Philosophy, and Pure Science, who helped bring Fermi to the United States and brought him together with representatives of the U.S. Navy Department for the first discussion of the atomic bomb) and Harold Urey (associate professor of Chemistry whose work on separation of isotopes resulted in the discovery of deuterium).[30] In addition, Columbia received visits from scientists at Princeton University who were coordinating their work with Columbia colleagues. These included John Wheeler, Edward Creutz,[31] and Robert R. Wilson.[30]

Metallurgical Laboratory[edit]

When Ashkin accepted an invitation to join the Manhattan Project he was still working on his Ph.D. He spent the last few months of 1942 at the Metallurgical Laboratory at the University of Chicago and then worked at the Los Alamos Laboratory from mid-1943 to mid-1945. The scientists at the Metallurgical Laboratory, or Met Lab as it was called, used a nuclear reactor called the Chicago Pile to produce the world's first controlled chain reaction.[32] They built the reactor in a disused squash court under the bleachers of Stagg Field, the university's old football stadium. They had been brought together from Columbia and Princeton by Arthur Compton who was a professor of physics at the University of Chicago. The Met Lab consisted of two divisions. Fermi, Anderson, Zinn, Creutz, and Szilard were key members of the physics division; Bethe and Teller of the theoretical division.[33]

Although Ashkin's interest, experience, and skill would seem to place him with the theoretical division, he worked in the physics division in a group called "Nuclear Physics — Experimental." His placement in this group suggests that Ashkin had prior experience in carrying out nuclear experiments while a student at Columbia. With the other members of the group — Feld, Szilard, Robert F. Christy, Herbert E. Kubitschek,[34] and S. Bernstein (untraced) — Ashkin produced a number of technical reports on the theoretical aspects of nuclear fission.[35][36][37][38] With Feld, he also produced a practical report on Poisoning and Production in a Power Plant which considered the power potential of sustained nuclear reactions as well as the radiation poisoning and other hazards that accompanied them. All these reports were secret when produced and have since been declassified and released.[37][39]

Los Alamos[edit]

At Los Alamos Ashkin was assigned to work in the Theoretical Division headed by Bethe. There were five groups in this division and Ashkin was assigned to group 4, Diffusion Problems. His responsibilities, broadly, permitted him to build upon work he had done as a graduate student and in his months at Met Lab. T-4's group leader was Richard Feynman; Ashkin was alternate leader. The initial members were Richard Ehrich,[40] and Frederick Reines. Theodore Welton (de) joined it in the early spring of 1944.[22][41] The group's main task was to estimate the rate at which neutrons would diffuse through the explosive core of the bomb during nuclear fission. Somewhat facetiously Feynman later claimed that the work done at Los Alamos was mostly engineering, not science.[42] Welton, however, told of the group's long hard hours, high spirits and cohesiveness, and said they achieved some excellent successes in theoretical physics.[43][44] Their work required a great number of mathematical computations, which, Welton remembered, they performed using Work Projects Administration math tables and big Marchant mechanical calculators. In fact, their assistant, an enlisted man named Murray Peshkin, remembered the group as having an unending need for calculation. An undergraduate with a major in physics at the time he was recruited, he was put, as he recalled, "to solving differential equations that were needed to predict the critical mass of a bomb under various assumptions about the many unknown properties of the nuclei in the bomb material."[45]

Security at Los Alamos was very tight by standards of the time. The site was an uninhabited desert location (formerly a private school) whose perimeter was fenced, with guards at the gates. The scientists were permitted outside the facility but there was little available transportation. (Since they were not members of the military, they could not be ordered to comply with military secrecy orders and instead voluntarily agreed to abide by them.)[42][46][47][48] Although urban-raised scientists, like Ashkin, were far from the amusements that cities afford, they were able to find amusing things to do. It helped that some of the married ones were able to bring their wives to live in the town of Los Alamos and thus parties of men and women could get together for social activities. These include such things as hikes of hills and canyons of the surrounding wilderness areas. It's likely Ashkin played outdoor team sports while at Los Alamos. A Met Lab colleague remembered playing touch football with him and Feld on an open space called the midway at the University of Chicago.[49]

Feynman was particularly adept at leavening hard work with light-hearted games. His genius was as much playful as serious. He took pride in deceiving the mail censors, guessing the combinations of safes in which secret files were stored, picking door locks, and teasing the guards (he would depart from the main gate, circle around the perimeter to a hole in the fence, re-enter the facility, and then exit the gate again, thus causing confusion and consternation both.) He also liked to pound his bongo drums, a practice which made those within hearing range grit their teeth but which he believed put him in touch with the spirits of the Indians who formerly inhabited the place. Physicists are known for their love of music, particularly classical music, and their ability to play it. Feynman wasn't unusual in his affection for drumming but his choice of musical genres was atypical as was his lack of skill as a drummer.[50] It appears that the music produced by his friends offended him as much as his relentless noise offended them. When Ashkin played the recorder, Feynman said he was using "an infernally popular wooden tube ... for making noises bearing a one-one correspondence to black dots on a piece of paper -- in imitation to music."[51]

In 1946, before the scientists at Los Alamos dispersed, there was a brief period during which they gave lectures on subjects in which they had expertise. The program was styled the "Los Alamos University" and some junior members of laboratory personnel received college credit for attending them. Ashkin's were on theoretical mechanics.[52] The course description says it covered the dynamics of particles, rigid bodies, elastic media, and fluids using vector analysis, particle dynamics, Lagrange's equations, and Hamilton's equations.[53]

Along with other members of the Feynman team, Ashkin produced technical reports while at Los Alamos. These were classified at the time but have since been made public. One example gives an idea of the work carried out by the group. It is The Calculation of Critical Masses Including the Effects of the Distribution of Neutron Energies, by Feynman, R.P.; Welton, T.A.; Ashkin, J.; Ehrlich, R.; Peshkin, M.; and Reines, F. Report LA-524(Del.) January 21, 1947 (extract from abstract: "Convenient approximate methods are developed for the calculation of critical sizes and multiplication rates of spherical, active cores surrounded by infinite tampers. Special attention is given to those problems arising from the fact that neutrons of different velocities have different properties. The methods consist essentially of approximating the neutron densities at each velocity by fundamental mode shapes for each velocity.")[54]

On July 16, 1945 Ashkin was present at the first-ever explosion of a nuclear bomb at the Trinity test site, Alamogordo. Only a few of the many scientists were permitted to witness this unspeakably dramatic culmination of their work. Ashkin was probably there because of his work on radiation poisoning, begun at Met Lab and probably continued afterward.[39]

In 1950 it was revealed that one of the scientists at Los Alamos, Klaus Fuchs, was providing the Soviet intelligence bureau, NKGB, with secret information about bomb research. Between 1943 and 1946, Fuchs worked at both Columbia and Los Alamos. When the FBI interviewed Bethe and Feynman about their relationship with Fuchs while at Los Alamos, Feynman said Fuchs was quiet, reserved and not inclined to mix with other scientists outside of work. He also said he believed Fuchs was less stand-offish with Ashkin and seemed friendly with him.[55]

Academic positions[edit]

University of Rochester[edit]

On leaving Los Alamos in 1946 Ashkin obtained a position as assistant professor at the University of Rochester and in 1950 he moved to the Carnegie Institute of Technology (later Carnegie Mellon University). He remained at CMU for the rest of his life, serving as professor and for a period head of the physics department.Robert Marshak brought Ashkin to the University of Rochester in 1946. As an assistant professor he taught mechanics and thermodynamics and theoretical physics and performed pioneering experiments on neutron-proton, proton-proton, and nucleon-nucleon scattering.[29][29][44][56][57][58][59]

While at Rochester, Ashkin was the first scientist to formally recognize the importance of the Feynman diagram. Feynman devised the diagram in 1948 to provide a simple visualization of the mathematical expressions governing the behavior of subatomic particles. Although the diagram and its offshoots were later seen as extremely important tools, Feynman did not give them a theoretical framework nor did he explain how he proposed they be used. Physicists had difficulty in understanding their function, distrusted their simplicity, and were reluctant to give them formal recognition. Feynman later said physicists did not realize the diagram's power and would employ a more complex method created by Julian Schwinger. Ashkin, he said, was the first to break with this pattern: "They somehow or other couldn’t do it. They had to go through this [the Schwinger method] to believe it. But that's all right. The only person who didn't, the first paper where it was used directly — which I kept looking for, I kept flipping through the Physical Review as it came out — was Ashkin. He'd done some calculation for some experiment, and he said, 'We’ve calculated this using Feynman's rules.' Bloop! There it was in writing! Then gradually more and more people did it."[60][61][62][63]

While he was teaching at the University of Rochester, Ashkin married Claire Ruderman, a biologist studying at the same university.[64][65] The couple had two daughters, Beth and Laura.[2]

Carnegie Mellon University[edit]

In 1950 Ashkin joined the physics faculty of Carnegie Mellon University (then the Carnegie Institute of Technology) where Edward Creutz was department head and director of a new 450 MeV proton synchrocyclotron that CIT had built in nearby Saxonburg, Pennsylvania.[29][31] Joining fellow scientists Lincoln Wolfenstein and Sergio de Benedetti,[66] at this time Ashkin began to transition from mainly theoretical to mainly experimental work. The cyclotron remained in use at the Saxonburg Nuclear Research Center until the mid-1970s when it was dismantled and, using it, Ashkin was able to produce some of his best-known experimental results.[67][68]

In 1953, with Bethe, his former director of theoretical work in Los Alamos, Ashkin published an article closely related to the work they had then done. This article, "Passage of Radiations Through Matter," summarized the effects of particles and radiation as they passed through solids.[69] In time it became a standard reference for physics experimenters.[29][70] Using the CIT cyclotron and following on work done by Bethe and Robert E. Marshak, Ashkin conducted experiments to determine the characteristics of a short-lived particle — the pi-meson or pion — that is produced when high energy cosmic ray protons and other cosmic ray components interact with matter in the Earth's atmosphere.[29][44][71] Ashkin served as chair of the physics department between 1961 and 1972.[28] After he died, CMU created the Julius Ashkin Teaching Award in his honor.[72]

Sabbatical at CERN[edit]

In 1958–1959 Ashkin won a Ford Foundation grant to spend a sabbatical year in Geneva, Switzerland, at CERN, the European Organization for Nuclear Research.[73] There, he became a member of the first group of scientists to use that institution's new 600 MeV synchrocyclotron.[74] Using this particle accelerator he helped to make a significant discovery which confirmed an aspect of the V-A Theory of weak interactions.[75][76][77][78] Supported by a grant from the Guggenheim Foundation, in 1968 he also spent a year as a Fellow at All Souls College, Oxford.[79]

Ashkin died on at Montefiore Medical Center on June 4, 1982 after a lengthy illness.[2][28]


  1. ^ Ashkin, Julius (1943). "Two problems in the statistical mechanics of crystals. I. The propagation of order in crystal lattices, II. The statistics of two-dimensional lattices with four components". Columbia University. Retrieved April 25, 2016. 
  2. ^ a b c "Julius Ashkin, 61, Physicist, Dies". New York Times. June 7, 1982. Retrieved April 25, 2016. 
  3. ^ "United States Census, 1930," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/X7X3-3YL : accessed December 23, 2013), Isadore Ashkin, Brooklyn (Districts 1251–1500), Kings, New York, United States; citing enumeration district (ED) 1261, sheet , family 298, NARA microfilm publication.
  4. ^ "United States World War I Draft Registration Cards, 1917–1918," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/KXY5-7XY : accessed December 23, 2013), Isadore Ashkin, 1917–1918; citing New York City no 86, New York, United States, NARA microfilm publication M1509, (Washington D.C.: National Archives and Records Administration, n.d); FHL microfilm 001765586.
  5. ^ "United States World War II Draft Registration Cards, 1942," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/F3CQ-T4W : accessed December 23, 2013), Isadore Ashkin, 1942.
  6. ^ "United States Census, 1920," index and images, FamilySearch (https://familysearch.org/pal:/MM9.1.1/MJRV-1VW : accessed December 23, 2013), Isdor Ashkin, Brooklyn Assembly District 18, Kings, New York, United States; citing sheet , family 342, NARA microfilm publication T625, FHL microfilm 1821173.
  7. ^ a b c "Catalogue Number for the Sessions of 1941–1942 and 1942–1943". Catalogue, Columbia University. 1940. Retrieved December 8, 2013. 
  8. ^ White-Orr's Reference Register. 1918. pp. 139–. 
  9. ^ "Madison High Graduates Told; Rev. Cornelius Greenway Tells Class to Prove School Benefit" (PDF). Brooklyn Daily Eagle. June 24, 1936. p. 30. Retrieved December 24, 2013. 
  10. ^ "212 From Boro and L.I. Win Scholarships" (PDF). Brooklyn Daily Eagle. August 28, 1936. p. 26. Retrieved December 24, 2013. 
  11. ^ "8 Pulitzer Price Scholarships Won By Students Here" (PDF). Brooklyn Daily Eagle. September 18, 1936. p. 3. Retrieved December 24, 2013. 
  12. ^ Aaserud, Finn (February 6, 1986). "Interview with Dr. William A. Nierenberg". Oral History Transcript. American Institute of Physics. Retrieved December 7, 2013. 
  13. ^ "Hugh Paxton 1909–2003" (pdf). Nuclear Criticality Safety Division Newsletter, American Nuclear Society: 5–6. Summer 2004. Retrieved December 9, 2013. 
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  15. ^ "Honors Upon Us" (PDF). Brooklyn Daily Eagle. March 13, 1938. pp. B7. Retrieved December 24, 2013. 
  16. ^ "News and Notices". The American Mathematical Monthly. 47 (5). May 1940. JSTOR 2302710. 
  17. ^ "73 Boro, L.I. Students in Columbia Class; Among 5,345 Seniors Who Will Get Degrees At 186th Commencement" (PDF). Brooklyn Daily Eagle. June 5, 1940. p. 30. Retrieved December 24, 2013. 
  18. ^ "Prizes and Fellowships Academic Honors". Columbia College Bulletin, Columbia University. Retrieved December 8, 2013. 
  19. ^ Ashkin, Julius; Nafe, John E.; Rothstein, Jerome (1942). "On the Limb Darkening of the Sun.". The Astrophysical Journal. 95: 76. Bibcode:1942ApJ....95...76A. doi:10.1086/144375. 
  20. ^ Ashkin, J.; Lamb, W. (1943). "The Propagation of Order in Crystal Lattices". Physical Review. 64 (5-6): 159–178. Bibcode:1943PhRv...64..159A. doi:10.1103/PhysRev.64.159. 
  21. ^ a b c Niss, Martin (2004). "History of the Lenz-Ising Model 1920?1950: From Ferromagnetic to Cooperative Phenomena". Archive for History of Exact Sciences. 59 (3): 267–318. doi:10.1007/s00407-004-0088-3. 
  22. ^ a b Silvan S. Schweber (1994). QED and the Men who Made it: Dyson, Feynman, Schwinger, and Tomonaga. Princeton University Press. pp. 585, 669. ISBN 978-0-691-03327-3. 
  23. ^ Longuet-Higgins, Christopher; Michael E. Fisher (1991). "Lars Onsager, 1903–1976, a Biographic Memoir" (pdf). National Academy of Sciences. Retrieved December 10, 2013. 
  24. ^ a b Lillian Hoddeson Senior Research Physicist University of Illinois; Ernst Braun Senior Research Physicist Institut fur Sozio-Okonomische Entwicklungsforschung; Jurgen Teichmann Senior Research Physicist Deutsches Museum; Spencer Weart Senior Research Physicist Center for History of Physics of the American Institute of Physics (11 September 1992). Out of the Crystal Maze : Chapters from The History of Solid State Physics: Chapters from The History of Solid State Physics. Oxford University Press, USA. ISBN 978-0-19-534532-2. 
  25. ^ Edward Teller; Judith Schoolery (9 September 2009). Memoirs: A Twentieth Century Journey in Science and Politics. Basic Books. pp. 156–. ISBN 978-0-7867-5170-9. 
  26. ^ "Physical Review – September 1943 Volume 64, Issue 5-6". Physical Review. 64 (5-6). September 1943. Retrieved December 10, 2013. 
  27. ^ Citations for Statistics of Two-Dimensional Lattices with Four Components, retrieved 2014-02-09 
  28. ^ a b c "About Julius Ashkin". Mellon College of Science Faculty Handbook, Carnegie Mellon University. Retrieved December 7, 2013. 
  29. ^ a b c d e f Wolfenstein, Lincoln. "Julius Ashkin". Physics Today. 35 (8): 66. Bibcode:1982PhT....35h..66W. doi:10.1063/1.2915225. Retrieved December 7, 2013. 
  30. ^ a b "Nuclear Fission, 1938–1942". Array of Contemporary American Physicists, American Institute of Physics. Retrieved December 9, 2013. 
  31. ^ a b Hinman, George (2010). "Edward Chester Creutz, 1913–2009, a Biographical Memoir" (pdf). National Academy of Sciences. Retrieved December 8, 2013. 
  32. ^ Allardice, Corbin; Edward R. Trapnell. "The First Pile" (PDF). International Atomic Energy Agency. Retrieved December 26, 2013. Originally written in 1946, this was the first comprehensive narrative account of the construction and operation of the world's first nuclear reactor. Though popular in approach and style, the story was written after extensive consultations with a number of the scientists directly associated with the great experiment, much of it being constructed from their personal recollections of what happened on 2 December 1942. The account is reprinted here by permission of the United States Atomic Energy Commission. 
  33. ^ "The Manhattan Project and predecessor organizations". Array of Contemporary Scientists, American Institute of Physics. Retrieved December 9, 2013. 
  34. ^ Leo Szilard; et al. (July 17, 1945). "A Petition to the President of the United States". U.S. National Archives, Record Group 77, Records of the Chief of Engineers, Manhattan Engineer District, Harrison-Bundy File, folder #76. Retrieved December 12, 2013. 
  35. ^ J. Ashkin; S. Bernstein; B. Feld; H. Kubitschek; L. Szilard, University of Chicago, U.S. Atomic Energy Commission (1947). Preliminary comparison of radon-boron and radium-beryllium neutron sources. Technical Information Division, Oak Ridge Operations. 
  36. ^ Ashkin, Julius; B. T. Feld (April 1, 1943). "Activation of Fast Neutron Detectors by Cyclotron and by Fission Neutrons". Technical Report CF-863 Metallurgical Lab University of Chicago. Retrieved December 12, 2013. 
  37. ^ a b Szilard, L.; Bernstein, S.; Feld, B.; Ashkin, J. (1948). "Inelastic Scattering of Fast Neutrons by Fe, Pb, and Bi". Physical Review. 73 (11): 1307–1310. Bibcode:1948PhRv...73.1307S. doi:10.1103/PhysRev.73.1307. 
  38. ^ Eugene Paul Wigner (2001). Historical and Biographical Reflections and Syntheses. Springer. pp. 148–149. ISBN 978-3-540-57294-7. 
  39. ^ a b Ashkin, Julius; Christy, R.F.; Feld, B.T. (December 15, 1942). "Poisoning and Production in a Power Plant". Technical Report CP-381; A-416 Metallurgical Lab, University of Chicago. Retrieved December 12, 2013. 
  40. ^ "Dr. Richard Ehrich, Obituary". Daily Gazette, Gainesville, Florida. January 31, 2002. 
  41. ^ "Theodore Allen Welton, Obituary". OakRidger, Oak Ridge, Tennessee. November 23, 2010. Retrieved December 13, 2013. 
  42. ^ a b Feynman, Richard (January–February 1976). "Los Alamos From Below: Reminiscences 1943–1945". Engineering and Science, California Institute of Technology. 39 (2). 
  43. ^ Welton, Theodore A. (2007). "Memories of Feynman". Physics Today. 60 (2): 46–52. Bibcode:2007PhT....60b..46W. doi:10.1063/1.2711636. 
  44. ^ a b c "Oral History Transcript — Dr. Robert E. Marsha, conducted by Dr. Charles Weiner at Professor Marshak’s Office, University of Rochester, Rochester, New York, June 16, 1970, Center for History of Physics of the American Institute of Physics". American Institute of Physics. June 16, 1970. Retrieved December 21, 2013. You see, we were so busy ... Those were rather brief years - for me almost two, for others three. The maximum time I guess, was about three and a quarter years. And these were very intense years. One really concentrated completely on the war work and trying to get that bomb built before the Germans. 
  45. ^ Peshkin, Murray (June 24, 2005). "To Be Young, Gifted and Building The Bomb". Chicago Tribune. Retrieved December 7, 2013. 
  46. ^ Lerner, BrendaWilmoth. "Manhattan Project". Espionage Encyclopedia. Retrieved December 15, 2013. 
  47. ^ Fuller, John. "Manhattan Project Organization". How the Manhattan Project Worked. How Stuff Works. Retrieved December 15, 2013. 
  48. ^ Rafalko, Frank J. (ed.). "Security and the Los Alamos Project". A Counter Intelligence Reader. II. U.S. National Counterintelligence Center. Retrieved December 15, 2013. 
  49. ^ Agnew, Harold M. (December 1982). "Early Impressions". Bulletin of the Atomic Scientists. 38 (10). Retrieved December 21, 2013. After being associated for 40 years with our nation's nuclear program it's difficult to select a particular incident which stands out above others. It may bemuse my colleagues to know what events I do not choose to write about on this occasion: events such as being with Enrico Fermi on December 2, 1942 under Staff Field; or being over Hiroshima on August 6, 1945; or playing touch football with Bernie Feld and the real Julius Ashkin (as opposed to the imposter who used Ashkin's name) on the Chicago Midway; or making a one-gram radium beryllium source on an afternoon in New York, putting it in a briefcase, and flying back to Chicago with it under my seat. 
  50. ^ Gold, Lauren (August 10, 2006). "Is it the mystery, or the structure, or the discipline? Whatever the reason, playing music seems to attract physicists". Cornell Chronicle. Retrieved December 16, 2013. 
  51. ^ Genius: The Life and Science of Richard Feynman. Vintage Books. 1992. p. 191. ISBN 978-0-679-74704-8. 
  52. ^ Ashkin, Julius; Keller, J.; Richman, C. "Technical Report AECU-167; (M-4297)". United States Office of Scientific and Technical Information. 
  53. ^ Truslow, Edith C.; Smith, Ralph Carlisle (1961). Manhattan District History: Project Y, the Los Alamos Project, Volume 2: August 1945 through December 1946 (PDF). Los Alamos Scientific Laboratory. Retrieved December 14, 2013. A part of the Manhattan District History commissioned by Leslie R. Groves. 
  54. ^ Feynman, Richard; et al. (January 21, 1947). "The Calculation of Critical Masses Including the Effects of the Distribution of Neutron Energies". Technical Report LA-524(Del.), Los Alamos Scientific Lab., N. Mex. 
  55. ^ "FBI Records - Klaus Fuchs - Part 6, Interviews with Associates of Fuchs". June 1950. Retrieved December 21, 2013. Feynman recalled that he believes Fuchs was friendly at Los Alamos with Dr. Julius Ashkin who is presently at the University of Rochester, Rochester, New York, and with Robert Eugene Marshak and his wife Ruth. 
  56. ^ Rickles, Dean (March 21, 2011). "Interview with Dr. Joshua Goldberg at Caltech University". Oral History Transcript. American Institute of Physics. Retrieved December 7, 2013. 
  57. ^ Ashkin, Julius; Wu, Ta-You (1948). "Neutron-Proton and Proton-Proton Scattering at High Energies". Physical Review. 73 (9): 973–985. Bibcode:1948PhRv...73..973A. doi:10.1103/PhysRev.73.973. 
  58. ^ Wu, Ta-YOU; Ashkin, Julius (1948). "Elastic and Inelastic Scattering of 100- to 200-Mev Protons or Neutrons by Deuterons". Physical Review. 73 (9): 986–1001. Bibcode:1948PhRv...73..986W. doi:10.1103/PhysRev.73.986. 
  59. ^ Ashkin, J.; Marshak, R. (1949). "Bremsstrahlung in High Energy Nucleon-Nucleon Collisions". Physical Review. 76 (1): 58–60. Bibcode:1949PhRv...76...58A. doi:10.1103/PhysRev.76.58. 
  60. ^ Weiner, Charles (June 28, 1966). "Interview with Dr. Richard Feynman at Altadena, CA". Oral History Transcript. American Institute of Physics. Retrieved December 7, 2013. 
  61. ^ Kaiser, David (2005). "Physics and Feynman's Diagrams". American Scientist. 93 (2): 156. doi:10.1511/2005.2.156. 
  62. ^ David Kaiser (2005). Pedagogy and the Practice of Science: Historical and Contemporary Perspectives. MIT Press. ISBN 978-0-262-11288-8. 
  63. ^ David Kaiser (November 15, 2009). Drawing Theories Apart: The Dispersion of Feynman Diagrams in Postwar Physics. University of Chicago Press. pp. 220–. ISBN 978-0-226-42265-7. 
  64. ^ Claire Ruderman Ashkin (1947). A Contribution to the Knowledge of Stridulating Organs in Spiders. University of Rochester. Department of Biology. 
  65. ^ American Association for the Advancement of Science (1948). Summarized Proceedings ... and a Directory of Members. The Association. 
  66. ^ "Sergio DeBenedetti--1912–1994" (pdf). Inter-Actions, Department of Physics, Carnegie Mellon University. 1995. Retrieved December 8, 2013. 
  67. ^ J. Steinberger (2005). Learning About Particles - 50 Privileged Years. Springer. ISBN 978-3-540-21329-1. The groundwork for the understanding of this resonance was done by Fermi and coworkers at the slightly higher energy Chicago cyclotron, which began to function in 1951. It was more definitively established by Ashkin and coworkers, using a yet slightly higher energy cyclotron at Carnegie Institute of Technology, which came into operation in 1953.... Fermi could almost reach it and Ashkin could finally see it clearly. (p. 53) 
  68. ^ Fetkovich, John (1997). "Saxonburg Cyclotron 50th Reunion" (pdf). Inter-Actions, Department of Physics, Carnegie Mellon University. Retrieved December 8, 2013. 
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