Radium Leads to Radioactivity

In the theory of atomic transformation the emanation of radium is the first product of disintegration and is transformed in its turn.

Continuing Early Science of Radioactivity,
with a selection from Lecture by Mme. Marie Curie published in NA. This selection is presented in 2 easy 5 minute installments. For works benefiting from the latest research see the “More information” section at the bottom of these pages.

Previously in Early Science of Radioactivity.

Time: 1903
Place: Paris

Some of the rays comprise electrified particles moving with very great velocity. Some are charged positively, and their dimensions are comparable with those of atoms; while others are negative electrons, whose electric charge may be shown by direct experiments. Admitting that all these projectiles come from the atoms of radium themselves, it is difficult to avoid the conclusion that the departure of a positive particle must necessarily cause a modification of the atom which expels it.

Among the electrons emitted there are some whose velocity is enormous, and is in fact no less than nine-tenths the velocity of light. It has been found that the mass of these projectiles (which are the most rapid that we know of) is greater than that of slower-moving electrons, and this result may be considered as a confirmation of the theory according to which the mass of an electron is regarded as the result of electromagnetic phenomena.

The energy of the rays of radium is also manifested by their capacity for exciting the luminosity of various phosphorescent substances. Radium salts are, indeed, themselves luminous, and the light is readily visible in certain conditions.

Here are now a new series of facts which are interpreted by the theory of radioactive transformation. Radium dis engages continuously a substance which behaves like a gaseous radioactive material and which has received the name of the emanation. Air which has been in contact with a solution of radium salts is charged with the emanation, and may be drawn away and studied. Air containing the emanation is strongly conducting. A sealed glass tube in which the emanation has been imprisoned acts on the outside like a radioactive substance, and is able, for example, to discharge an electroscope. When the emanation is drawn into a flash containing zinc sulphide, the latter becomes luminous. The emanation is an unstable gas and spontaneously disappears, even from a sealed glass tube, at a rate in accord with a strict law, by which a given quantity of emanation diminishes by half in about four days. The emanation possesses the property of imparting radioactivity to all the bodies in contact with it, and such bodies are said to possess induced radioactivity.

In the theory of atomic transformation the emanation of radium is the first product of disintegration and is transformed in its turn. The induced radioactivity to which it gives rise is considered as due to a solid radioactive material, which results from the transformation of the radium emanation. Three different radioactive materials are distinguished in the induced radioactivity, which constitute three successive terms of the transformation. Each transformation is also accompanied by the emission of rays, and the expelled particles are also counted among the resulting products.

Induced radioactivity does not disappear completely; but there remains after the lapse of a day a very feeble residue which persists in part for years, and which is believed to be adding new terms to the series of successive transformations.

A new fact of great interest has come to the support of the theory of the transmutation of radioactive substances, and has, indeed, made it almost indispensable. It has been proved that radium, a perfectly definite chemical element, produces continually another perfectly definite chemical element, helium (Ramsay and Soddy). It is admitted that helium is one of the products of the disintegration of the atom of radium, and it is noteworthy that helium occurs in all the radium-bearing minerals.

The theory of the radioactive transformation has been extended to all the radioactive bodies, and investigations have been made to determine if the radioactive substances hereto fore considered as elements are not to be derived from one another. The origin of radium itself has been sought in uranium. It is well known that radium is found in the uranium-bearing minerals, and it appears from recent re searches that the proportion between the quantities of radium and uranium is the same in all these minerals. Uranium may, then, be thought of as a mother substance, which disintegrates with extreme slowness, giving place to the production of radium and the products which succeed it. It appears also to be probable that the last term of the radioactive series is polonium. It may be recalled that uranium was the substance in which the property of radioactivity was discovered by M. Becquerel, and polonium is the first new substance which was discovered by the aid of radioactivity.

A series of analogous considerations has been established for another radioactive substance — thorium. In this case thorium as a primary substance generates radiothorium, a substance recently discovered, which gives rise to the gaseous radioactive emanation of thorium and various products of radioactivity induced by this emanation. Actinium also gives place to a series of transformations similar to those of thorium, and it, like radium, produces helium.

I have already stated that radioactivity is a general property of matter. If the theory of radioactive transformation continues to inspire a growing degree of confidence, it will result in an important consequence for geology, and will lead to a careful study of the proportions of the elements occurring in rocks, with a view to deduce their relative ages.

It is plain that the hypothesis of radioactive transformation is well adapted to the present state of the science of radioactivity. It was among those proposed by M. Curie and myself at the beginning of our researches on radioactivity; but it has received its precise development by Rutherford and Soddy, to whom it is for this reason generally attributed. It seems to me, however, better not to leave the domain of demonstrated facts, and not to lose sight of other explanations of radioactivity which have been proposed. The actual state of the science does not seem to me far enough advanced to warrant a positive conclusion.

In closing, the general importance of the phenomena of radioactivity may be recalled. For physics the radioactive substances constitute a new implement of research in consequence of the rays they emit, and they have actively contributed to the development of the theory of the conduction of gas and of the nature of the electron. By their numerous chemical and physiological effects, and their possible influence on meteorology, these substances extend their sphere of action in the domain of all the science of nature; and it is probable that their importance for the development of science will go on increasing. Finally, it has been shown that there is nothing absurd in supposing that the energy we receive from the sun may be in part, or even in total, due to the presence of radioactive bodies which it may contain.

Mme. Marie Curie begins here. Sir William Ramsay begins here. Sir Oliver Lodge begins here.

More information here and here, and below.

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