During the Middle Ages the desire to find a way to convert a base metal
like lead into gold was the outstanding incentive for research in
chemistry. When the important role of the nucleus in determining the
chemical properties of an atom became clear and the natural
transmutation accompanying radioactivity was understood, the fascinating
idea occurred to many people that perhaps man would soon be able to
alter the nucleus of a stable atom and thus deliberately convert one
element into another. In a historic lecture delivered in Washington, D.
C., in April 1914, Rutherford said, “It is possible that the nucleus of
an atom may be altered by direct collision of the nucleus with very
swift electrons or atoms of helium (i.e., beta or alpha particles) such
as are ejected from radioactive matter.... Under favorable conditions,
these particles must pass very close to the nucleus and may either lead
to a disruption of the nucleus or to a combination with it.”
[Illustration: _Medieval Alchemist_
Courtesy Fisher Scientific Company]
World War I began shortly after Rutherford made this statement, and
preoccupation with war work stopped his experiments with nuclei. In
1919, however, he published a paper describing what happens when alpha
particles pass through nitrogen gas. Very fast protons, or hydrogen
nuclei, appear to originate along the paths of the alpha particles. The
following is from Rutherford’s paper:
“If this be the case, we must conclude that the nitrogen atom is
disintegrated under the intense forces developed in a close collision
with a swift alpha particle, and that the hydrogen atom which is
liberated formed a constituent part of the nitrogen nucleus.... The
results as a whole suggest that, if alpha particles or similar
projectiles of still greater energy were available for experiment, we
might expect to break down the nuclear structure of many of the lighter
atoms.”
This prediction has certainly been verified through the use of the
atomic artillery provided by extremely powerful particle accelerators,
or “atom smashers.”[1]
[Illustration: _The Bevatron accelerator at the University of
California’s Lawrence Radiation Laboratory, Berkeley, California,
shown after recent remodeling in which it was enclosed in concrete
shielding._
Courtesy Lawrence Radiation Laboratory]
Patrick Blackett in England and W. D. Harkins in the United States soon
proved independently that, during the nuclear event reported by
Rutherford in his 1919 paper, an alpha particle combines with a nitrogen
nucleus and that the resulting unstable combination immediately emits a
proton and ends up as one of the isotopes of oxygen. This was the first
instance of deliberate transmutation of one stable chemical element into
another. Since that time practically every known element has been
transmuted by bombardment. The dream of the alchemists has been
partially fulfilled in that mercury has been changed into gold. We say
“partially fulfilled” because the process is much too expensive to be
economically profitable.