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.”
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]
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.