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Radioactive tracers.

Fourteen years before, Knoop had used benzene rings as a tracer in fat metabolism (see 1904). It occurred to the Hungarian-born chemist Georg Karl von Hevesy (1885-1966) that it might be possible to use radioactive atoms as tracers. The advantage would be that their concentration could be accurately determined even when they were present in trace quantities, thanks to the radiations they emitted.

In 1918 Hevesy decided to make use of a radioactive isotope of lead, formed by uranium breakdown. This radiolead was identical in chemical properties to ordinary stable lead. Suppose, then, he were to add a small quantity of radiolead to lead and use the mixture to produce certain lead compounds.

These lead compounds are only slightly soluble in water, so that one could not measure the concentration of the dissolved stable lead with anything approaching accuracy. If, however, a lead compound with radiolead added is stirred in water so that a tiny fraction of the molecules dissolve, that same tiny fraction of the molecules containing radio-lead also dissolves. The amount of radio-lead in solution can then be easily and accurately determined, and the percentage of radiolead compound dissolved will be the same as that of the ordinary lead compound.

In later years, Hevesy followed the manner in which plants absorbed and distributed water by spiking it with a tiny quantity of radiolead compound that he could follow accurately.

As long as radioactive tracing was confined to lead, it could only play a minor role, of course. Nevertheless, Hevesy had pointed out the potential of the technique, and the time was to come when it was to be a superb and essential tool for biochemists and others.

For this, and for other work, Hevesy was awarded the Nobel Prize for chemistry in 1943.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
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