|
|
|
| Current Issue |
|
|
| Resources |
|
|
|
Power and Poison
| Article
# : |
19272 |
|
|
Section : |
NATURAL SCIENCE
|
| Issue
Date : |
7 / 1991 |
3,165 Words |
| Author
: |
Harold Goldwhite
Harold Goldwhite is professor of chemistry at California
State University, Los Angeles. |
One age-old goal of the alchemists, the predecessors of chemists, was transmutation--changing one element into another. Alchemical literature is full of obscure procedures that allegedly changed lead or mercury into precious gold. Transmutation became a scientific reality rather than an alchemical dream in 1896 when Henri Becquerel discovered the radioactivity of uranium, observing that this heaviest of all naturally occurring elements was spontaneously emitting energetic particles and radiation. This new area of science was spectacularly advanced two years later when Marie and Pierre Curie discovered two new radioactive elements, polonium and radium.
Early in the twentieth century Ernest Rutherford and Frederick Soddy deduced from their studies of radioactivity that transmutation did occur in the radioactive decay of uranium. Ironically, the end product of that change was lead, the starting material for many alchemical transmutation attempts. All the natural radioactive transmutations discovered at that time produced lighter elements from heavier ones.
Soon after the neutron was discovered by James Chadwick in 1932, different scientific groups began to use this neutral particle to try to synthesize new artificial elements heavier than uranium; these elements, not normally found in nature, are now called transuranium elements. In 1940 a group led by Edwin M. McMillan in Berkeley, California, obtained the first evidence that transuranium elements could be prepared. Neutron capture by the most common isotope of uranium, U-238, produced a new radioactive isotope, U-239. This isotope decayed by loss of an electron to produce an isotope of the first transuranium element, which was called neptunium, symbolized Np. In the numerical arrangement of the elements in which the lightest, hydrogen, is number 1, and the heaviest naturally occurring element, uranium, is 92, neptunium is element number 93.
Later in 1940 the Berkeley group subjected U-238 to bombardment by the nuclei of heavy hydrogen (deuterium) in a large cyclotron, or particle accelerator. This produced a new isotope of neptunium that emitted an electron and was transformed into the second of the transuranium elements, number 94, which was named plutonium. (Elements 92, 93, and 94 are named for the outer three planets, Uranus, Neptune, and Pluto.) The study of the preparation and chemical properties of the new elements became a central theme for one of McMillan's collaborators, Glenn Seaborg. [For more on Seaborg, see "Transuranium Pioneer," pp. 310-319.]
Significant
...
Read Full Article
Look for this article in Ask.com
|
|
