Discovery Of Artificial Radioactivity Research Articles

The Discovery of Artificial Radioactivity

We reconstruct Frederic Joliot and Irene Curie’s discovery of artificial radioactivity in January 1934 based in part on documents preserved in the Joliot–Curie Archives in Paris, France. We argue that their discovery followed from the convergence of two parallel lines of research, on the neutron and on the positron, that were focused on a well-defined experimental problem, the nuclear transmutation of aluminum and other light elements. We suggest that a key role was played by a suggestion that Francis Perrin made at the seventh Solvay Conference at the end of October 1933, that the alpha-particle bombardment of aluminum produces an intermediate unstable isotope of phosphorus, which then decays by positron emission. We also suggest that a further idea that Perrin published in December 1933, and the pioneering theory of beta decay that Enrico Fermi also first published in December 1933, established a new theoretical framework that stimulated Joliot to resume the researches that he and Curie had interrupted after the Solvay Conference, now for the first time using a Geiger-Muller counter to detect the positrons emitted when he bombarded aluminum with polonium alpha particles.

The history of the discovery of nuclear fission

Following with the discovery of the electron by J. J. Thomson at the end of the nineteenth century a steady elucidation of the structure of the atom occurred over the next 40 years culminating in the discovery of nuclear fission in 1938–1939. The significant steps after the electron discovery were: discovery of the nuclear atom by Rutherford (Philos Mag 6th Ser 21:669–688, 1911), the transformation of elements by Rutherford (Philos Mag 37:578–587, 1919), discovery of artificial radioactivity by Joliot-Curie and Joliot-Curie (Comptes Rendus Acad Sci Paris 198:254–256, 1934), and the discovery of the neutron by Chadwick (Nature 129:312, 1932a, Proc R Soc Ser A 136:692–708, 1932b; Proc R Soc Lond Ser A 136:744–748, 1932c). The neutron furnished scientists with a particle able to penetrate atomic nuclei without expenditure of large amounts of energy. From 1934 until 1938–1939 investigations of the reaction between a neutron and uranium were carried out by E. Fermi in Rome, O. Hahn, L. Meitner and F. Strassmann in Berlin and I. Curie and P. Savitch in Paris. Results were interpreted as the formation of transuranic elements. After sorting out complex radio-chemistry and radio-physics O. Hahn and F. Strassmann came to the conclusion, beyond their belief, that the uranium nucleus split into smaller fragments, that is nuclear fission. This was soon followed in 1939 by its theoretical interpretation by L. Mietner and O. Frisch.

The Neutron – The Curie Family's Legacy

This article is concerned with the scientific developments that led to the discovery of the neutron by Sir James Chadwick at the Cavendish Laboratory Cambridge in 1932. The Rutherford atom with a heavy nucleus and the problem of the ‘intra-nuclear’ electrons (needed to reconcile nuclear mass and charge) coupled with Marie Curie's discovery of radium as a prime example of natural radioactivity coming from the nucleus were key milestones. Frédéric Joliot and Irène Curie–Joliot almost discovered the neutron in 1931. But the predisposition of the thinking in Chadwick's laboratory allowed conclusive identification of the emission of a heavy neutral particle to be published about a month after the Curie–Joliot experiment. Their Nobel Prize came a few years later with the discovery of artificial radioactivity.

Enrico Fermi’s Discovery of Neutron-Induced Artificial Radioactivity: Neutrons and Neutron Sources

We reconstruct and analyze the path leading from James Chadwick’s discovery of the neutron in February 1932 through Frederic Joliot and Irene Curie’s discovery of artificial radioactivity in January 1934 to Enrico Fermi’s discovery of neutron-induced artificial radioactivity in March 1934. We show, in particular, that Fermi’s innovative construction and use of radon-beryllium neutron sources permitted him to make his discovery.

French contributions to electron microscopic radioautography.

Radioautographic effects result from properties of ionizing radiations which act on a special photographic emulsion by leaving tracks in silver halide crystals. The phenomenon was observed in 1896 by Henri Becquerel [4] working at the Museum National d'Histoire Naturelle in Paris, by placing accidentally a crystal of uranium salt on a photographic plate protected from light. When he later developed the plate forgotten in a drawer, he was astonished to observe that the form of the uranium crystal was imprinted on the photographic emulsion. Becquerel gave first an erroneous interpretation of this unexpected phenomenon: he thought it was caused by some unknown radiations secondarily emitted by the phosphorescent property of this mineral. However, this impression could be reproduced when the crystal was left in a darkroom. Hence, he postulated that uranium itself was able to produce radiations which could not be detected by the eye but by photographic emulsion. His contribution to the discovery of the natural radioactivity was rewarded by a Nobel prize he shared with Made and Pierre Curie in 1903. In fact, Becquerel not only discovered radioactive radiations, but he invented simultaneously the principle of radioautography: the uranium crystal reproduced its outline by emitting radiations which were registered in the photographic emulsion. The principle of this method was applied 30 years later to detect the site of natural radioactive atoms in biological samples. In 1924, A Lacassagne and J Latt~s [39] at the Institut Curie imagined to place a photographic plate in contact with slices of organs previously embedded in paraffin blocks. When rabbits were given polonium, the radioactive radiations emitted, by polonium incorporated into the organs produced a blackening of the photographic plates. Thus the images provided a distribution of polonium in various tissues, but this technique did not allow to obtain a resolution at the cellular level and if one excepts radiotoxicological investigations, radioautographic applications of natural radioactivity were rather limited. A new impulse was given by the discovery of artificial radioactivity; FrEdEric and Irene Joliot-Curie, working at the Coll~ge de France, opened indeed new vistas to radioautography by extending the production of a great variety of radioactive isotopes which have been proved to be essential tools to put forth new concepts in physiology, pharmacology and medicine. As early as 1938, F Joliot, fascinated by the biological applications of this discovery, asked A Lacassagne to collaborate. The latter proposed CP Leblond, a young histologist educated at the FacultE catholique de mEdecine de Lille, to study the location of the 128I iodine isotope, produced by cyclotron, in the thyroid gland by radioautography [44]. This project was interrupted by World War II, but the idea remained in Leblond's mind. In 1943, he used another isotope of iodine and succeeded to obtain tracks in thyroid follicles [42]. It was necessary however to improve resolution. Leblond, now in Montreal, was conscious that a major pitfall was the distance between the radioactive source contained in tissue sections and the photographic emulsion used as detector of radiations. Moreover, a direct superimposition of the radioactive tracks and of the subjacent histological structures was required. With these goals in mind, BElanger and Leblond [5] devised in 1946 the so-called 'coating technique' of radioautography in which a gently-warm, liquid photographic emulsion is directly applied in close contact with the tissue sections. The thin film of coated emulsion adheres directly to the subjacent structures and reduces therefore the interspace between the radioactive source and the detector. After developing the radioautographs, the silver grains are visualized over the tissues or cells enclosing the radioactive tracer. Simultaneously, nuclear physicists devised new emulsions especially enriched in small-sized silver halide crystals, called 'nuclear emulsions'. A better knowledge of the interactions between nuclear emulsions and radiations permitted to obtain highsensitivity detection at minimum ionization (reviewed in [45]); a lowering of the detection threshold of beta-emitting isotopes was improved by activation procedures of the emulsion for light and for electron microscopy (reviewed in [52]). Since resolution, sensitivity and yield of the nuclear emulsion were also improving, the principle of the 'coating technique' could be adapted and applied to electron microscopic preparations.

Early days of fission

There were four main steps in the sequence of events leading to the discovery of fission, made just over 50 years ago. There was the discovery of the neutron by Chadwick in 1932; then two years later the discovery of artificial radioactivity by Irene Curie and Frederic Joliot, quickly followed by Fermi's use of the neutron to induce artificial radioactivity, leading eventually to the discovery of fission in early 1939.

Nuclear physics: A report on the Paris conference

Being an affair organized on the occasion of the thirtieth anniversary of the discovery of artificial radioactivity by Frederick and Irene Joliot‐Curie, the Paris Conference on Nuclear Physics had, and was supposed to have, aspects of both a conference and of a show. Several factors contributed to its eminent success as a conference. In chronological order of impact, the first of these was the elevated spirits induced, at least for non‐Parisians, just by the magic of Paris. The second was the excellence of the facilities and of the organization. The third was the high quality of the papers and, in general, of their presentation. The last, but in the end the most important, factor was the impression of the vitality, one even may say rebirth, of nuclear physics as a field.

Rehovoth Conference on Nuclear Structure

From September 8 to 15 an international gathering of physicists took place for the first time in the small new state of Israel. The 220 participants registered at the conference included 155 guests from countries ranging alphabetically from Argentina to Yugoslavia. The choice of the Weizmann Institute of Science in Rehovoth, Israel, as the location of the International Conference on Nuclear Structure was undoubtedly in recognition of Israel as a center of that particular kind of nuclear research which has made the name Racah familiar in laboratories throughout the world. However, in his opening address to the conference, Professor Racah found other links between nuclear structure and the State of Israel. The first Zionist Congress, said Racah, was held at about the same time as the discovery of radioactivity; the Balfour Declaration announcing British Government support for a Jewish National Home in Palestine was promulgated at about the same time as the discovery of artificial radioactivity; and in 1948 the State of Israel was born together with the shell model. To avoid being accused of partisanship with regard to nuclear models, however, he pointed out that one of the distinctive features of Israel were the collective settlements.

Radioactive iodine in the treatment of the hyperthyroidism of nodular goiter.

IN PRESENTING to this group the clinical results of the use of radioactive iodine in the treatment of the hyperthyroidism of nodular goiter, there seems little necessity to review the history of the initial discovery of artificial radioactivity, the subsequent production of radioactive iodine, and the part such iodine has played and is playing in the study, diagnosis, and treatment of thyroid disease. In this paper, we consider it more important to confine ourselves to the presentation of the end results of our treatment, together with some evaluation of these results. Methods During the past two years, radioactive iodine has been used at the Cleveland Clinic in the treatment of hyperthyroidism. The patients with nodular goiters who were selected for this therapy have all been 40 years of age or older. The solitary adenoma has never been chosen for such treatment. Radioactive iodine was used in several instances of large nodular goiters because the patient was averse to the idea of operation. In some of o...

RADIO IODINE: ITS USE AS A TOOL IN THE STUDY OF THYROID PHYSIOLOGY*

WITH the discovery of artificial radioactivity by Joliot and Curie (1), the building of the cyclotron by Lawrence and his associates (2, 3), and the development of the uranium chain reacting pile (4), the physicists have offered to biologists and physicians valuable tools for the study of intermediary metabolism. Indeed, the discovery of radioactive tracer techniques has been likened in importance (5, 6) to the invention of the microscope. The particular advantage of studies with these techniques lies in their applicability to the investigation of metabolic processes in physiologic equilibrium. As Marine (7, 8, 9, 10) and his associates demonstrated in 1915 and 1916, the thyroid gland is unique in that it has the ability to collect iodine selectively in relatively large quantities. It is, therefore, not surprising that studies with the radioactive isotopes of iodine have proved readily applicable and illuminating in the study of thyroid physiology.

The Use of Radioactive Tracers in Biology and Medicine

A very large share of investigative work in the biological sciences has been devoted to the study of the metabolism of organisms ranging in complexity from bacteria to man and embracing the more important members of the plant and animal kingdoms. Until the discovery of artificial radioactivity by Curie and Joliot in 1934 (1), the only method for studying the mechanisms whereby the various elements and compounds essential for life are assimilated, distributed throughout the tissues, converted into other compounds, and finally eliminated, was by a direct chemical approach to these problems. This mode of attack, although very productive of information, suffers from several serious limitations. First, in order to observe the manner by which a living organism metabolizes an element, as, for example, potassium, it is necessary to administer enough so that a detectable increase in the amount in the body will be produced. This axiom applies to most of the elements and compounds that are normal constituents of biological systems. Normally, the content of these substances is kept in most instances within relatively narrow limits by the body and for this reason it is necessary to administer a sufficient quantity of the element or compound to disturb this carefully regulated balance if fluctuations are to be produced that are large enough to be accurately determined by analytical chemical technics. It is obvious that such procedures will frequently disturb the normal chemical and physiological processes of the organism, and the experimental data thus obtained may not present a true picture of the normal metabolism of the substances that are being studied. Second, it is not possible by chemical procedures to differentiate between the atoms or molecules of the administered material and those that are already present in the tissues of the plant or animal. For example, the increase in excretion of phosphorus by an animal following the administration of this element is made up in part by the phosphorus atoms already in the body, which were displaced by the administered element, and in part by a portion of the phosphorus given to the animal. The classical procedures of chemistry and physics do not permit the investigator to determine what proportion of the phosphorus atoms in the excreta came from the administered material and the fraction that was displaced from the pre-existing phosphorus in the tissues. This limitation applies to all metabolic investigations in which the elements or compounds are constituents of the organism that is being studied. The first attempt to circumvent these limitations was made by Hevesy in 1923 (2), when he employed a radioactive isotope of lead (radium D) to investigate the metabolism of that element in plants. His procedure made it possible to measure quantitatively the uptake and distribution of the administered lead by determining the radioactivity of the different portions of the plant.

Applied Nuclear Physics

Following the discovery of artificial radioactivity and the rarer stable isotopes of the light elements, the forty-year-old field of applied nuclear physics has found a greatly increased domain of usefulness in chemistry, metallurgy, radiology, geology, physiology and medicine. Isotopic tracer atoms, whether stable or radioactive, provide a powerful method for observing the behavior of complicated biological, chemical or physical systems under equilibrium conditions. Atom smashing machines, when slightly modified, are useful in metallurgical and clinical radiology, while other techniques and results from the field of nuclear physics find important applications in geology and astrophysics.

Neutron Capture and Nuclear Constitution

AMONG the properties of atomic nuclei disclosed by the fundamental researches of Lord Rutherford and his followers on artificial nuclear transmutations, one of the most striking is the extraordinary tendency of such nuclei to react with each other as soon as direct contact is established. In fact, almost any type of nuclear reactions consistent with energy conservation seems likely to occur in close nuclear collisions. In collisions between charged particles and nuclei, contact is, of course, often prevented or made less probable by the mutual electric repulsion; and the typical features of nuclear reactions are therefore perhaps most clearly shown by neutron impacts. Already in his original work on the properties of high-speed neutrons Chadwick recognised their great effectiveness in producing nuclear transmutations1. Especially after the discovery of artificial radioactivity by Mme and M. Joliot-Curie, most instructive evidence regarding nuclear reactions has been obtained through the researches of Fermi and his collaborators on radioactivity produced by bombardment with high-speed neutrons as well as with neutrons of thermal velocities2.