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

NUCLEAR PHYSICS AND RADIO PROPAGATION
proton, the charge-to-mass ratio of the electron, and the first precise de-
termination of the proton moment in absolute units.11'
A new instrument, the omegatron, also came out of the atomic physics
division. Basically a miniature cyclotron about the size of a pack of cig-
arettes, the omegatron made possible determination of the values of several
important atomic constants with much higher precision than heretofore. In
addition, the faraday, previously determined solely by electrochemical
measurements, was for the first time evaluated directly by physical methods,
the preliminary value obtained representing a slight but significant degree of
greater precision over that obtained with either the silver or iodine voltam-
eter. The omegatron also facilitated sharper determination of the magnetic
moment of the hydrogen
The formulation within a year or two of three proposed basic stand-
ards—length, determined by the green line of mercury 198; the gyromagnetic
ratio of the proton, a constant to which the standard of mass might be re-
ferred; and time, in the constant natural frequency of the Bureau's atomic
clock (see below, pp. 476—477)—led some at the Bureau to hope that "a com-
plete set of primary atomic standards" might not be far ofT. They saw an in-
creasing number of primary references for physical measurements—the
independent and arbitrarily defined units of the last century—replaced by a
set of working definitions comprising an atomic meter, atomic second, atomic
ampere, atomic newton, atomic coulomb, and atomic kilogram."3
The year 1946 saw the inception of Bureau research in tracer
raphy, that is, the tracking of the movement of radioactive atoms through
organic systems, and later through inorganic systems as well. With radio-
active isotopes made available by the Atomic Energy Commission (iodine 131,
cobalt 60, phosphorus 32, sodium 22), tracers rapidly became an important
tool of research in chemistry, biology, medicine, and industry.
A comparison check made by the Bureau disclosed discrepanices in
medical and other research laboratories of several hundred percent in the
determinations of amounts of radioactive material in samples of substances
being used for medical treatment. The Bureau at once began work on stand-
ards for quantitative measurement of each of the tracer elements. Before
H. A. Thomas, R. L. Driscoll, and J. A. Hipple, "Measurement of the proton move-
ment in absolute units," Phys. Rev. 75, 902 (1949), and Phys. Rev. 78, 787 (1950);
Driscoll, Thomas, and Hipple, "The absolute value of the gyromagnetic ratio of the
proton," Phys. Rev. 79, 339 (1950) ; NBS Annual Report 1949, pp. 19—20; Annual Report
1951, p. 29.
112 J• A. Hipple, H. Sommer, and H. A. Thomas, "A precise method of determining the
faraday by magnetic resonance," Phys. Rev. 1877 (1949); NBS Annual Report
1950, pp. 6, 34.
" R. D. Huntoon and U. Fano, "Atomic definition of primary standards," Nature, 166
167 (1950).
469