Heresy, György

Heresy, György

(b. Budapest, Hungary, 1 August 1885; d. Freiburg im Breisgau, Germany, 6 July 1966)

radiochemistry, physical chemistry, analytical chemistry, biochemistry.

Hevesy came from a family of wealthy industrialists ennobled by Franz Joseph I (he signed his name when writing in German as von Hevesy). He attended the Piarist Gymnasium in Budapest and then entered the University of Budapest, where he studied physics and chemistry. He continued his education in Berlin and Freiburg. In 1908 he received his doctorate for an investigation of the interaction between fused sodium and sodium hydroxide. Hevesy began his scientific career as an assistant to Richard Lorenz at the University of Zurich. He soon moved to the Technische Hochschule in Karlsruhe in order to study catalytic processes at Fritz Haber’s institute. To his regret, Haber directed him to investigate whether molten zinc emits electrons. Because there was no one in Karlsruhe with experience in measuring radiation, Hevesy went to Rutherford at Manchester in order to acquaint himself with radioactive materials.

Rutherford’s laboratory was then one of the few investigating radioactive phenomena. Many of the observations made there had the effect of unsettling the structure of classical physics and chemistry to its very foundations. There the first great generation of atomic scientists grew to maturity. Nearly all the young people then working at the laboratory became world-famous researchers. Hevesy formed an especially close friendship with Niels Bohr.

The first great surprises regarding radioactive elements had already been experienced. Rutherford had announced that radioactivity is caused by the transmutation of elements. Consequently one must conclude that atoms are composite entities, and Rutherford began to develop his conception of the planet-like structure of the atom. Many decay products of the natural radioactive series had already been identified. In his radioactive displacement rule Soddy had previously stated the relation by which radioactive daughter elements, which he named “isotopes,” are listed in the periodic table. According to this rule, elements of different atomic weights must have the same location in the table. At the time it remained unclear whether isotopes are in fact fully identical in chemical terms. Rutherford himself was not certain on this point. When the laboratory received from Austria a by-product from the preparation of uranium containing so much natural lead that it absorbed the radiation of the radium D (a lead isotope) present in it, he told Hevesy: “If you are worth your salt, separate radium D from all that nuisance of lead.”

Hevesy began the work necessary to fulfill this request. The separation of the radium D from the lead was not accomplished through any chemical means. He first had to realize that isotopes are not chemically separable. He continued his work at the Radium Institute in Vienna with Paneth. Although radium D cannot be separated from lead, lead can be “marked” (detected and traced) by the radiation of the admixed radium D. In 1913 Hevesy published “Über die Löslich leit des Bleisulfids und Bleichromats” in Zeitschrift für anorganische Chemie (82 [1913], 323–328), which brought him the Nobel Prize for chemistry. The introduction to this work summarizes the essential aspects of radioactive tracing:

The fourth decay product of radium emanation, RaD, shows, as is well known, the chemical reactions of lead. If one mixes the RaD with lead or lead salts, the former cannot be separated from the lead salts, the former cannot be separated from the lead by any chemical or physical methods; and once the complete mixing of the two materials has taken place, the concentration ratio remains the same even for arbitrarily small amounts of lead that one removes from the solution. Since RaD, as a result of its activity, can be detected in incomparably smaller amounts than lead, it can thus serve as a qualitative and quantitative proof of [the presence of] lead, to which it is attached: RaD becomes an indicator of lead.

The Nobel Prize did not come to Hevesy for thirty years (he received it in 1943). The reason for the thirty-year delay was that nearly all discoveries of Hevesy were premature. As long as scientists dealt with only the few natural radioactive isotopes, the radioactive tracing techniques possessed a very restricted range of application, as did all the other “radio tracer” and radioanalytic methods that Hevesy developed in the meantime. Their importance greatly increased when, through the invention of the production techniques for artificial radioactive isotopes, these methods found many applications.

After 1913 Hevesy contributed much to the definitive clarification of the question of isotopes (“Zur Frage der isotopen Elemente,” in Physikalische Zeitschrift, 15 [1914], 797–804). After having unambiguously established their chemical identity, he demonstrated the identity of their electrochemical properties. He also aided H. G. Moseley in his work on the relationship of the frequency number of the Kα line and the chemical atomic number.

Hevesy—on vacation in Hungary when World War I was declared—served in the Austro-Hungarian army. After the war he was a Privatdozent at the University of Budapest. With Gyula Gróh he applied his “marking” method to demonstrating the autodiffusion of metal ions in the crystal lattice, tracing in particular the autodiffusion of radium D in solid lead. With Laszlo Zechmeister he showed that radioactivity was equally divided between salts crystallized from the mixture of inactive lead chloride and “labeled” lead nitrate. When a solution of a “labeled“lead salt was mixed with that of an organic lead compound, the activity was retained in the original salt. Arrhenius greeted this experiment as a significant and striking proof of his ionic theory.

The turbulent postwar political situation in Hungary impelled Hevesy to leave the country. In 1920 he went to Copenhagen and worked with his friend Bohr, who had become a professor.

In the periodic table only four spaces were not occupied. One of the missing elements possessed the atomic number 72. Element 71, lutetium, belonged to the rare earths. It had long been supposed that element 72 also belonged to that group, and thus it was sought in monazite sand, a source of rare earths. On the basis of Bohr’s newly worked-out theory of electron configuration, with seventy-two electrons a new orbital should open up. Consequently, element 72 ought to be similar to zirconium rather than to the rare earths. On this supposition, Hevesy and Dirk Coster began the radiographic examination of zirconium ores and were able to demonstrate in them the line of an unknown element, which they then isolated chemically in the form of a fluoride. They named it hafnium after the Latin name of Copenhagen (Nature, 111 [1923], 78–79, 182).

Also in 1923 Hevesy reported that with the help of radium D he had traced the absorption of lead in plants; this was the first application of the radioactive tracer technique to biology (Biochemical Journal, 17 [1923], 439–445). There followed the investigation of the distribution of bismuth in the animal body (a rabbit) with the aid of an active bismuth isotope, which marked the first use of the tracer method in medical research.

In 1926 Hevesy was called to the University of Freiburg im Breisgau. There, with E. Alexander, he observed that when the elements of higher atomic number are subjected to X rays, a characteristic secondary emanation begins that can be used in the detection and determination of the element in question (Nature, 128 [1931], 1038–1039). In this way the method of X-ray fluorescence analysis was discovered. Because this method was not feasible with the equipment then available, it would not prevail in practice for twenty years. A further achievement during Hevesy’s stay at Freiburg was the invention, with R. Hobbie, of the isotope dilution method, which enriched analytical chemistry with a completely new technique. Using it, they were able to determine the lead content of rocks (Nature, 129 [1932], 315).

Politics again affected Hevesy’s career. After the Nazis came to power he was forced to leave Germany. He returned to Copenhagen, where he once more enjoyed the hospitality of the Bohr Institute. Until this time Hevesy had made all his discoveries with the few naturally radioactive isotopes, thus narrowing their field of possible application. In 1934 the Joliot-Curies produced the first artifically radioactive element by means of neutron irradiation, thereby beginning a period in which artificially radioactive isotopes of almost all the elements could be produced. The importance of the radioactive tracer method therefore increased rapidly. Today there is hardly a branch of science or technology in which this procedure is not used.

For analytic purposes, Hevesy immediately drew upon the Joliot-Curie method of transmuting elements through neutron irradiation. In 1935 he and Hilde Levi developed the method of neutron activation analysis, now among the most important microanalytic procedures and indispensable in testing the extremely pure materials required by modern technology. They described the first application as follows:

We used the method of artificial radioactivity to determine dysprosium content of yttrium preparations. The procedure was the following: we mixed 0.1%, 1% etc. of dysprosium... and determined the intensity obtained. The yttrium sample to be investigated was then activated under exactly the same conditions and a comparison of the dysprosium activities obtained gave 1% as the dysprosium content... [Kongelige Danske Videnskabernes Selskabs Skrifter, Math. Medd., 14 (1936), 5–34].

Hevesy was the first to use an artificially produced isotope as a tracer. He produced P³² through neutron irradiation (1935) according to Joliot’s method and immediately used the preparation to study phosphorus metabolism in rats. Thus began his extensive biochemical activity, in which he employed a great many isotopes to investigate medicochemical problems—for example, to examine the distribution of elements in the body and in carcinomas, and to study the formation of blood corpuscles, of DNA, and of other substances.

In 1942, following the German occupation of Denmark, Hevesy made a perilous escape to Sweden, where he continued his work at the University of Stockholm.

In addition to the Nobel Prize, Hevesy received other major scientific awards, including the Faraday, Copley, and Bohr medals, the Fermi Prize, the Ford Prize, and the second Atoms-for-Peace Award.

BIBLIOGRAPHY

I. Original Works. hevesy’s most important periodical publications were collected in Adventures in Radioisotope Research, 2 vols. (Oxford, 1962), which includes a complete bibliography and an autobiography entitled “A Scientific Career.” Among his books are Lehrbuch der Radioaktivität (Leipzig, 1923), written with H. Paneth; and Die seltenen Erden vom Standpunkt des Atombaues (Berlin, 1927).

II. Secondary Literature. See H. Levi, “George de Hevesy,” in International Journal of Applied Radiation and Isotopes, 16 (1965), 512–524; and Nuclear Physics, 98 (1967), 1–24; and F. Szabadváry, “Geogrge Hevesy,” in Journal of Radioanalytical Chemistry, 1 (1968), 97–102.

Ferenc SzabadvÁry