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

378 WORLD WAR II RESEARCH (1941-45)
"so closely guarded that the Bureau's participation in the atomic bomb proj-
ect was not known to the members of the staff not associated with the
undertaking."
This, of course, was not entirely so. Even before the close of the
photoelectric phase of the proximity fuze project in 1943, when most of
that group were sent out to Los Alamos, many at the Bureau suspected or
knew generally that some kind of new weapon using uranium was under
development. Yet so weighted was the wrap of secrecy that even some direct-
ly involved in research on "Tuballoy," the Briticism adopted by the Bureau
as the code name for uranium, had no inkling of the real purpose of their
research.4° Wholly engrossed in his determination of the energy states of
uranium, one member of the Bureau recalls thinking that the metal might
be for a new type of small power plant, possibly for airplanes, to enable them
to carry bigger bomb loads, or for submarines, in order to carry a larger
store of torpedoes. "The last thing in the world I thought the uranium could
be used for was in a bomb," he was to say.41 The story of that secret re-
search bears retelling.
In the year after verification in this country of the splitting of the
uranium atom, Enrico Fermi sought to demonstrate a chain reaction in na-
tural unconcentrated uranium. His colleague at Columbia, John R. Dunning,
was investigating the two isotopes of uranium, the rare 235, less than 1 per-
cent of the natural element, and the abundant isotope 238, comprising 99.3
percent of the element. In March 1940, Dunning conclusively demonstrated
that was the isotope that fissioned with slow neutrons.42
That same spring Edwin M. McMillan and Philip H. Abelson at the
University of California made an even more spectacular discovery; that
neutron absorption by U238 resulted in two new elements with atomic num-
bers 93 and 94. They were named neptunium (Np) and plutonium (Pu).
Study of the latter indicated it was probably as fissionable by thermal (slow)
neutrons as U235. So nebulous was the "bomb project" at that stage, how-
ever, that further investigation of plutonium was delayed while McMillan
went off to MIT to work on a more pressing matter, radar.43
'° Briggs, NBS War Research, p. 8.
"Tuballoy" came from "Tube Alloys," the meaningless and unintelligible expression
used by the British for their uranium bomb program.
41 Interview with Dr. Carl C. Kiess, May 1, 1964. For Harold Urey's similar reaction
concerning his heavy water research, see ch. VI, p. 359n.
Hewlett and Anderson, The New World, 1939—1946: A History of the United States
Atomic Energy Commission, pp. 13—14, 22.
Ibid., pp. 33—34; McMillañ and Abelson, "Radioactive element 93," Phys. Rev. 57,
1185 (1940). The discovery held out the possibility that element 94 could be pro-
duced in a pile and then separated chemically, without the tremendous expense of build-
ing isotope separation plants. Moreover, if plutonium was fissionable it would utilize
all but a small fraction of the metal in a natural uranium pile.