Marie Curie ca. 1920. Inset: Pierre Curie (Marie's favorite picture of her husband). The quartz balance, devised by Pierre Curie and his brother Jacques, was essential for Marie's work. (Photo ACJC

By the time he met Marie Sklodowska, Pierre Curie had already established an impressive reputation. In 1880, he and his brother Jacques had discovered piezoelectricity whereby physical pressure applied to a crystal resulted in the creation of an electric potential. He also had made important investigations into the phenomenon of magnetism including the identification of a temperature, the curie point, above which a material's magnetic properties disappear. However, shortly after his marriage to Marie in 1895, Pierre subjugated his research to her interests.  Together, they began investigating the phenomenon of radioactivity recently discovered in uranium ore. Although the phenomenon was discovered by Henri Becquerel, the term radioactivity was coined by Marie. After chemical extraction of uranium from the ore, Marie noted the residual material to be more "active" than the pure uranium. She concluded that the ore contained, in addition to uranium, new elements that were also radioactive. This led to their discoveries of the elements of polonium and radium, but it took four more years of processing tons of ore under oppressive conditions to isolate enough of each element to determine its chemical properties.  For their work on radioactivity, the Curies were awarded the 1903 Nobel Prize in physics. Tragically, Pierre was killed three years later in an accident while crossing a street in a rainstorm. Pierre's teaching position at the Sorbonne was given to Marie. Never before had a woman taught there in its 650 year history! Her first lecture began with the very sentence her husband had used to finish his last. In his honor, the 1910 Radiology Congress chose the curie as the basic unit of radioactivity: the quantity of radon in equilibrium with one gram of radium (current definition: 1 Ci = 3.7x1010 dps). A year later, Marie was awarded the Nobel Prize in chemistry for her discoveries of radium and polonium, thus becoming the first person to receive two Nobel Prizes. For the remainder of her life she tirelessly investigated and promoted the use if radium as a treatment for cancer. Marie Curie died July 4, 1934, overtaken by pernicious anemia no doubt caused by years of overwork and radiation exposure.

In December of 1897 Marie Curie began obtaining data for her doctoral dissertation by investigations into the rays emitted by uranium.  Her "laboratory" was a storage area in the "School of Physics and Chemistry" where Pierre taught. M. Curie wanted to make a quantitative study of the "uranic" rays. This seemed to be best done by making electrical measurements since Becquerel and others after him had shown that the rays could ionize air.  She and Pierre were able to develop a measurement technique using the precision piezoelectric quartz balance and electrometer that Pierre had invented along with his brother Jacques Curie. (The Curie brothers had discovered piezo electricity.)

Her technique involved the use of an ioniztion chamber, which basically consisted of parallel conducting plates. Ionized air between the plates provides a conduction path and the current, I, can be measured.

In Curie's case the plates were 8 cm. in diameter and separated by 3cm. A voltage V, of about 100V was used. Currents, I, were typically in the range of picoamperes ( 10^-12A).

On April 12, 1898, Marie Curie's first paper was presented at the Academy of Sciences (Paris). There were three important conclusions:

1) She discovered a new active substance, thorium. This is actually an independent discovery of the same result that G. C. Schmidt of Erlangen Germany had announced in February of 1898. She had analyzed a large number of other substances and found no activity. The discovery that thorium too produced penetrating rays meant that this phenomenon could no longer be "uranic rays". It was of a more general nature than being a peculiarity of uranium.

2) All uranium compounds are active. The more uranium they contain, the more active they are.

3) The careful quantitative results of M. Curie allowed her to note that pitchblende (rich in uranium oxide) and chalcite( rich in uranyl phosphate) had anomalously high activity, much more than uranium itself.
"They are much more active than uranium itself. This fact is very remarkable and leads one to believe that these minerals contain an element which is much more active than uranium."

This observation established a new technique for identifying elements, namely by noting their radioactive properties.

The Curies then began to try and isolate the active element from pitchblende. By the beginning of May 1898 they finally isolated a very active product which they thought was pure enough to investigate spectroscopically. This sample showed no discernible new spectral lines. They continued their chemical distillations of the pitchblende products so that by June they had products 300 times more active than uranium. By this time they had come to conclude that their were two new active elements hiding in the pitchblende, one which accompanied bismuth and another which accompanied barium in the breakdown from pitchblende.

They tried spectroscopy again, with the aid of an expert, but again could not find spectroscopic evidence of a new substance. Despite the lack of a spectroscopic signal they felt their evidene based on the activity of the bismuth companion was sufficient to give their new element a name, Po, polonium, after Marie's home country.

On July 18, H. Becquerel read a paper contributed by the Curies ( neither were members of the Academy) entitled "On a new radio-active substance contained in pitchblende" to the Academy. Note that this is the first introduction of the word "radioactivity" into the scientific lexicon.

The next step of their research that year was to try to find spectroscopic evidence for the other radio-active element carried off with the barium. By October they had received another shipment of pitchblende. By the end of November, with the help of Gustave Bemont, a spectroscopist at the EPCI where Pierre taught, they had produce a barium product which had an activity 900 times that of uranium. Spectroscopic analysis of this sample by an eminent spectroscopist (Eugene Demarcay) revealed a new spectral line. By the end of December 1898 they were able to send off their next report to the Academy. It was read on December 26, 1898. A note was attached from Demarcay "This ray ( i.e. spectral line) does not appear to me to be attributable to any known element ... its presence confirms the existence, in small quantity, of a new element in the barium chloride of M. and Mme Curie."
This element is Radium.

Marie Curie was determined to isolate radium so as to be able to measure it's atomic weight and to prepare compounds of it. Even the highly active samples they had isolated with barium from the pitchblende did not contain enough radium that they could measure a difference in mass between their sample and an ordinary sample of barium chloride. Pierre was more interested in the phenomenon of radioactivity itself. The task of separating out radium in weighable quantities became Marie's quest.

Since radium was present in such tiny amounts in pitchblende large quantities of pitchblende were needed. Also, this work would entail considerable space. The Curies were given a drafty hangar at EPCI. On rainy days they had to work inside the hangar on the chemical treatments. Otherwise they did the processing outside. With financial aid from Baron Edmond de Rothschild they obtained more than ten tons of pitchblende from the Joachimsthal mine. This is residue left over from uranium mining. By Spring 1899 Marie had everything she needed to do the separation. Over the next few years Marie's highly active barium samples were sought after by several physicsts and chemists. The Curies were able to investigate the effects of magnetic fields on the emissions from radium.
Finally in July 1902 Marie was able to present a paper to be read at the Academy announcing that she had succeeded in obtaining 0.1g of radium out of her mountain of pitchblende. She concluded that its atomic weight was 225 (226 is the modern value) and that it should appear in the periodic table after barium under the column of alkaline earth metals.

It was very important to be able to isolate radium and measure its chemical and atomic properties. Frederick Soddy, in 1904, noted that all the other radioactive substances occurred in such minute quantities that their only evidence of existence was their radioactivity. In 1924 Jean Perrin stated "It is not an exaggeration to say today that the isolation of radium is the cornerstone on which the entire edifce of radioactivity rests."

PUBLIC FASCINATION WITH RADIUM

Radioactivity and radium were fascinating subjects for the general public.
Quite soon it was realized that tremendous energy was available in radioactive atoms. By 1905 everyone who could read knew about radium.
From Susan Quinn's book, p 196:
"The usual tendency of the popular press to exaggerate the practical benefits of scientific discovery was carried to wild extremes in the case of radium. ... Charles H, Gage in San Francisco, a man who 'has a laboratory and calls himself professor,' claimed he could ' run a big automobile filled with passengers a distance of 300 miles' on batteries charged with his 'new radium preparation'. "

It was soon recognized that radioactivity could be useful in the treatment of cancer. However, quacks were quick to sell radioactivity as a cure all, examples: ( from Susan Quinn's book - p 410 )
- a radioactive "Curie Hair Tonic" which stopped hair loss and returned it to its original color
- a "Creme Activa" which promised eternal youth accompanied by a statement that " Madame Curie ... promises miracles."
- from 1929, a list of eighty patent medicines with radioactive ingredients which came in the form of bath salts, liniment, suppositories, toothpaste, chocloate candies, etc.
However, reputable physicians also used "radium therapy" for a range of illnesses besides cancer. Soldiers in WWI were given intravenous injections of radium solutions in cases of extreme blood loss, and external applications of radium and radon to soften scar tissue, loosen joints and stimulate nerve function. Marie Curie herself supplied sources for such treatment during the war.

http://musee.curie.fr/presentation/musee.html Une "petite boutique du radium"  présente différents produits des années vingt reflétant l'engouement que connaissait le radium à cette époque. Parmi ces produits, une fontaine à eau radioactive, des publicités vantant la laine pour bébé "la laine Oradium" ou la crème de beauté "Tho-Radia" !

Even as early as 1904 it was known that high doses of ionizing radiation could be lethal. Pierre Curie's last papers dealt with radiation effects on mice and guinea pigs. He himself showed signs of radiation illness in the years before he died in a street accident in 1906. Marie Curie died of pernicious anemia in 1934.

The Radium Institute

After the Curies were awarded the Nobel prize in 1903, Pierre was offered a position as professor at the Sorbonne. As a part of the contract hiring him the University agreed to build a new laboratory to house the "Radium Institute" as well as an adjoining institute for medical research.

Pierre's death in a street accident in 1906 left his position unfilled. Marie Curie was offered is duties, but not his position, at the Sorbonne. She directed the Radium Institute until her death in 1934. Researchers at this institute discovered other radioactive elements. It was also the site of the first production of artificial radioactivity and almost the site where the neutron was discovered.