Measures for Progress: A History of the National Bureau of Standards

THE BUREAU AND THE ATOMiC BOMB
With attention focused on the work at Columbia, three crucial ques-
tions confronted Dr. Briggs and his advisory committee in the early sum-
mer of 1940: (1) Were there any circumstances under which a chain reaction
could actually be achieved? (2) Could the isotope 235 be separated on a
large scale? (3) Could moderators such as graphite or heavy water and other
materials be obtained of sufficient purity and in sufficient quantity?
The possibility that deuterium (heavy water) might be a better
moderator of a chain reaction than graphite was not overlooked. The Bri-
tish were convinced that a chain reaction would go in relatively small units
of uranium and heavy water, and in February 1941 Urey at Columbia began
investigating mdthods for large-scale concentration of deuterium.45 Al-
though heavy water proved more effective than graphite in slowing down
neutrons and showed a smaller neutron absorption, its high efficiency in
much smaller quantities than graphite was outweighed by the difficulties oi
producing useful amounts. Subsequent experiments with a uranium and
heavy-water pile demonstrated that such a pile couJd not be shut down as
completely or as rapidly as the graphite pile. Important as heavy water
was in later nuclear weapons research, and in scientific, biological, and in-
dustrial research, it played little part in the wartime achievement.46 Pro-
curement, therefore, centered on graphite.
A group at the Bureau under Clement J. Rodden at once started work
on methods of analysis for the development of a highly purified graphite.
Because of the strong neutron-absorbing characteristics of the boron found
in the commercial product, a graphite low in boron was absolutely essential.
The work of Rodden in devising a reliable method for boron determination,
later successfully applied to boron in uranium as well, enabled carbon manu-
facturers to produce a much more highly purified graphite. By the middle
of 1942 this problem was essentially solved.47
Two investigations into the possibility of separating the isotopes of
uranium started in the fall of 1940. At Columbia a group under Dunning
"Smyth, Atomic Energy for Military Purposes (Smyth Report), p. 55.
"A fine summary of British encouragement of and contributions to the project appears
in Groves, Now It Can Be Told, pp. 406—408. See also report of the Directorate of Tube
Alloys, Statements Relating to the Atomic Bomb (London: Her Majesty's Stationery
Office, 1945), pp. 13 if; its summary in Rev. Mod. Phys, 17, 472 (1945); and Margaret
Cowing, Britain and Atomic Energy, 1939—1945 (London: Macmillan, 1964).
Smyth Report, pp. 95, 147—149, 153. In July 1942, marking the genesis of the hydrogen
bomb, Oppenheimer first disclosed the theoretical calculations of his group at California
indicating "that a much more powerful reaction than nuclear fission might be produced
by the thermonuclear fusion of deuterium, the heavy hydrogen isotope," and therefore
"the possibility of a * * * weapon using a more easily attainable material" than or
U". Hewlett and Anderson, p. 104.
4TSmyth Report, p. 95; NBS War Research, p.8.
379