Early Science of Radioactivity

This series has seven easy 5 minute installments. This first installment: Ms. Curie on Early Radioactive Research.

Introduction
This is the story of the beginnings of the Atomic Age. Authorities before World War I did not yet know how consequential sub-particle physics would be to civilization and, indeed, to the planet as a whole. This is how they saw it at the time.

The selections are from:

• Lecture by Mme. Marie Curie.
• Presidential Address to the British Association for the Advancement of Science by Sir William Ramsay published in either 1911 or 1912.
• a special aticle to The Great Event Evemts by Famous Historians, Volume 20 by Sir Oliver Lodge published in 1914.

For works benefiting from the latest research see the “More information” section at the bottom of these pages.

Summary of daily installments:

We begin with Mme. Marie Curie (1867-1934). She was one of the great heroes of science. She won two Nobel Prizes, one in Physics and later one in Chemistry.

Time: 1903
Place: Paris

When one reviews the progress made in the department of physics within the last ten years, he is struck by the change which has taken place in the fundamental ideas concerning the nature of electricity and matter. The change has been brought about in part by researches on the electric conductivity of gas, and in part by the discovery and study of the phenomena of radioactivity. It is, I believe, far from being finished, and we may well be sanguine of future developments. One point which appears to-day to be definitely settled is a view of atomic structure of electricity, which goes to conform and complete the idea that we have long held regarding the atomic structure of matter, which constitutes the basis of chemical theories.

At the same time that the existence of electric atoms, indivisible by our present means of research, appears to be established with certainty, the important properties of these atoms are also shown. The atoms of negative electricity, which we call electrons, are found to exist in a free state, independent of all material atoms, and not having any properties in common with them. In this state they possess certain dimensions in space, and are endowed with a certain inertia, which has suggested tL t idea of attributing to them a corresponding mass.

Experiments have shown that their dimensions are very small compared with those of material molecules, and that their mass is only a small fraction, not exceeding one one-thousandth of the mass of an atom of hydrogen. They show also that if these atoms can exist isolated, they may also exist in all ordinary matter, and may be in certain cases emitted by a substance such as a metal without its properties being changed in a manner appreciable by us.

If, then, we consider the electrons as a form of matter, we are led to put the division of them beyond atoms and to admit the existence of a kind of extremely small particles, able to enter into the composition of atoms, but not necessarily by their departure involving atomic destruction. Looking at it in this light, we are led to consider every atom as a complicated structure, and this supposition is rendered probable by the complexity of the emission spectra which characterize the different atoms. We have thus a conception sufficiently exact of the atoms of negative electricity.

It is not the same for positive electricity, for a great dis similarity appears to exist between the two electricities. Positive electricity appears always to be found in connection with material atoms, and we have no reason, thus far, to believe that they can be separated. Our knowledge relative to matter is also increased by an important fact. A new property of matter has been discovered which has received the name of radioactivity. Radioactivity is the property which the atoms of certain substances possess of shooting off particles, some of which have a mass comparable to that of the atoms themselves, while the others are the electrons. This property, which uranium and thorium possess in a slight degree, has led to the discovery of a new chemical element, radium, whose radioactivity is very great. Among the particles expelled by radium are some which are ejected with great velocity, and their expulsion is accompanied with a considerable evolution of heat. A radioactive body constitutes then a source of energy.

According to the theory which best accounts for the phenomena of radioactivity, a certain proportion of the atoms of a radioactive body is transformed in a given time, with the production of atoms of less atomic weight, and in some cases with the expulsion of electrons. This is a theory of the trans mutation of elements, but differs from the dreams of the al chemists in that we declare ourselves, for the present at least, unable to induce or influence the transmutation. Certain facts go to show that radioactivity appertains in a slight degree to all kinds of matter. It may be, therefore, that matter is far from being as unchangeable or inert as it was formerly thought; and is, on the contrary, in continual transformation, although this transformation escapes our notice by its relative slowness.

Let us now consider the essential facts revealed by the study of radioactive substances, and examine them from the point of view of the hypothesis of the atomic transformation of matter. Among the radioactive elements, some appear to be permanently active (uranium, thorium, radium, actinium), while others lose their radioactivity little by little (polonium). The most powerful representative of the permanently radioactive substances is radium. According to the theory of transformation this substance changes very slowly, so that a given mass of radium would lose half its weight only in several thousand years. Consequently the quantity of radium which disappears from a gram of this substance in an hour is absolutely inaccessible to experiments. However, a gram of radium disengages each hour about 100 calories of heat. To conceive how enormous this disengagement of heat is, we remark that during the life attributable to radium the complete transformation of a gram of this substance would produce as much heat as the combustion of a ton of coal. The transformation of radium, then, if transformation there be, is not to be regarded as an ordinary chemical reaction, for the quantity of heat involved is of a far higher order. One is led to conceive, rather, that the atoms themselves are transformed, for the quantities of energy put in play in the formation of atoms are probably considerable.

Indeed, the phenomenon of radioactivity has a palpably atomic character, which was brought to light in the beginning of researches on the subject. It was precisely the absolute conviction that we were dealing with an atomic phenomenon which led M. Curie and me to the discovery of radium. If the radioactivity cannot be separated from the atom it is very difficult to conceive anything but the atom itself involved in the transformation.

The effects produced by radium are very powerful, considering how small is the quantity of this substance at disposal for experiments. There is a spontaneous and continuous emission of rays, analogous to those which we know are produced by means of an induction coil in a Crookes tube, and these rays produce ionization of gas in the same manner. They are able, for example, to produce the rapid discharge of an electroscope. The energy of the rays is so great that the discharge is produced even across a thick metallic screen, for the rays can traverse such a screen.

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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