Pierre Curie

by Marie Curie

As for the polonium, I have not been able to isolate it, its quantity in the mineral being even much less than the quantity of radium. However, very concentrated polonium has been prepared in my laboratory, and important experiments have been performed with this substance, concerning especially the production of helium by radiation of polonium.

I had to devote special care to the improvement of the measuring methods in the laboratory. I have told how important precise measurements were in the discovery of radium. It is still to be hoped that efficient methods of quantitative determination may lead to new discoveries.

I devised a very satisfactory method for determining the quantity of radium by the means of a radioactive gas produced by it and called "emanation." This method, frequently used in my laboratory, permits of the measurement of very small quantities of radium (less than a thousandth of a milligramme), with a fair precision. More important quantities are often measured by their penetrating radiation, named Gamma-rays. For this we also possess in my laboratory a suitable equipment. It is easier and more satisfactory to measure the radium by the emitted rays, than to weigh it in a balance. However, these measurements require the disposition of reliable standards. So the question of a radium standard had to be taken into careful consideration.

The measurements of radium had to be established on a solid basis, for the benefit of laboratories and scientific research, which, of course, is in itself an important reason, and moreover, the growing medical utilization of this substance made it necessary to control the relative purity of commercially produced radium.

The first experiments on the biological properties of radium were successfully made in France with samples from our laboratory, while my husband was living. The results were, at once, encouraging, so that the new branch of medical science, called radiumtherapy (in France, Curietherapy), developed rapidly, first in France and later in other countries. To supply the radium wanted for this purpose, a radium-producing industry was established. The first plant was created in France and worked very successfully, but afterwards manufactures were founded in other countries, the most important of which are now in America, where great quantities of radium ore, named "carnotite," are available. The radiumtherapy and the radium production developed conjointly, and the results were more and more important, for the treatment of several diseases, and particularly of cancer. As a consequence of this, several institutes have been founded, in the large cities, for the application of the new therapy. Some of these institutes own several grammes of radium, the commercial price of the gramme being now about $70,000, the cost of production depending on the very small proportion of radium in the ore.

It may be easily understood how deeply I appreciated the privilege of realizing that our discovery had become a benefit to mankind, not only through its great scientific importance, but also by its power of efficient action against human suffering and terrible disease. This was indeed a splendid reward for our years of hard toil.

The success of the therapy depends, of course, on the precise knowledge of the quantity of radium which is used, so that the measurements of radium are as important for industry and for medicine as for physicochemical research.

Considering all these needs, a commission of scientific men of different countries was formed who agreed to take as a base an international standard, formed of a carefully weighed quantity of pure radium salt. Secondary standards were then to be prepared for each country, and compared to the basic standard by means of their radiation. I was appointed to prepare the primary standard.

This was a very delicate operation, as the weight of the standard sample, quite small (about 21 milligrammes of chloride), had to be determined with great precision. I performed the preparation in 1911. The standard is a thin glass tube, of a few centimeters in length, containing the pure salt which was used for the determination of atomic weight. It was accepted by the Commission and is deposited in the International Bureau of Weights and Measures at Sèvres, near Paris. Several secondary standards, compared with the primary one, have been put into service by the Commission. In France the control of radium tubes, by the measurement of their radiation, takes place in my laboratory, where any one may bring the radium to be tested; in the United States this is done in the Bureau of Standards.

Near the end of the year 1910, I was proposed for the decoration of the Légion of Honor. A similar proposal was made earlier in favor of my husband, who, however, being opposed to all honorary distinctions, did not accept the nomination. As my husband and I were too united in all things for me to act differently from him in this matter, I did not accept the decoration, in spite of the insistence of the Ministry. At that time also, several colleagues persuaded me to be a candidate for election to the Academy of Sciences of Paris, of which my husband was a member during the last months of his life. I hesitated very much, as such a candidacy requires, by custom, a great number of personal visits to Academy members. However, I consented to offer myself a candidate, because of the advantages an election would have for my laboratory. My candidacy provoked a vivid public interest, especially because it involved the question of the admission of women to the Academy. Many of the Academicians were opposed to this in principle, and when the scrutiny was made, I had a few votes less than was necessary. I do not ever wish to renew my candidacy, because of my strong distaste for the personal solicitation required. I believe that all such elections should be based wholly on a spontaneous decision, without any personal efforts involved, as was the case for several Academies and Societies which made me a member without any demand or initiative on my part.