In this installment on the history of atom theory, physics professor (and my dad) Dean Zollman discusses Pierre and Marie Curie’s pioneering and dangerous work to isolate radium. – Kim
By Dean Zollman
Pierre and Marie Curie had discovered radium by measuring the radioactivity of pitchblende, an ore from which uranium was extracted. The radioactivity of pitchblende was much greater than that of pure uranium. In fact they found two different levels of radioactivity which led them to conclude that two different elements – radium and polonium – were present in the ore. As I discussed last time, the conclusions were good enough for most physicists to believe the discovery, but the chemists wanted to see the isolated elements. So, Pierre and Marie Sklodowska Curie undertook the task of separating the elements, particularly radium, from the pitchblende.
Separating radium from the pitchblende was not easy. As I noted last time, they had a laboratory to work in, even if it was space considered not good enough for cadavers. Then, of course, they needed to obtain the ore.
In one way, that was easy. Large quantities of pitchblende were available from a mine in Bohemia owned by the Austrian-Hungarian government. The ore was considered useless because the uranium had already been extracted from it. The Curies could have the ore at no cost; they just needed to transport it from the mine to Paris. An anonymous benefactor, believed by some historians to have been Baron Edmond de Rothschild, provided the funds to transport the material from Bohemia to Paris. So, they obtained several tons of pitchblende, which was delivered in large sacks.
The process of separating the radium from the ore was a tedious application of chemistry. It involved many steps in which the ore was ground, dissolved in acids and other liquids, separated or filtered, and tested for radioactivity. Once they had a residue which was more radioactive than the material that they started with, they repeated the process. A reasonable description of the process is shown in an episode of The Six Experiments That Changed the World.
This video must have used material other than pitchblende. The actors in the video are much too cavalier in their handling of their “pitchblende.” Today’s safety standards for handling radioactive material would not allow the approach shown in the film. They also use modern equipment. For, example, Marie and Pierre did not have a Geiger counter. However, the video does represent reasonably well the way that the Curies handled pitchblende. They had no idea about the dangers of radioactive substances.
A particularly nasty element of which they knew nothing is radon. Today, we are told to test our basements for this radioactive gas because it is quite harmful. It is a product of the radioactive decay of radium. Because the processes that the Curies were using involved frequent boiling of the materials, they were without doubt releasing this radioactive gas and then breathing it.
They were able to get some help, particularly from André Debierne and industrial firm, Central Chemical Products Company, which sold some of the scientific instruments invented by Pierre. The company took on some of the initial steps in the extraction with Marie concentrating on the final steps. After three years of tedious work, they were able to obtain one-tenth of a gram of radium chloride from about one ton of pitchblende.
Conducting this research was not the Curies’ only effort. Both of them were teaching. In addition, in 1897 Marie gave birth to their first daughter, Irene.
Both the hazards and benefits of radioactivity were quickly discovered. After hearing of a couple of burns incurred by other scientists, including Henri Becquerel, Pierre taped some radioactive barium to his arm. The result was a red burn that took 52 days to heal. By this time both Marie and Pierre were noticing that their fingers were sometimes hardened and painful. Some of these experiences led to experiments about the health benefits of radioactivity. Reports of cures or reduction in tumors were published. Many good books and web pages can provide much detail on the how radium and other radioactive elements were used and mostly misused in the early 20th century, so I will not pursue that topic further. Instead, I will focus on a few stories about the Curies.
What’s the Source of Radiation?
On the scientific side was the question of where the radioactive particles came from. Were they somehow emitted from the atom or did the atom do something to its surroundings and cause them to be created there? At the time of this discussion, the nucleus had not been discovered (more about that next time), so everyone talked of the atom as the smallest unit of an element. Ernest Rutherford took the view that these radioactive emissions were coming from the atom. Pierre Curie argued in favor of the radium atom causing the emissions to come from the surrounding material. Of course, neither of them had any experimental evidence for his point of view. Eventually, Pierre came around to Rutherford’s view, but until much later no evidence was available to support either of them.
Pierre and Marie Curie were nominated for the Nobel Prize for the first two years that it was given. However, they were passed over. In the third year of the prize, a rather strange event happened. Four members of the French Academy of Science sent a letter to the Nobel Committee in which they gave all of the credit for isolating radium to Pierre. They nominated Pierre Curie and Henri Becquerel for the prize and omitted Marie.
The committee that considers the nominations is supposed to work in strict confidence. However, one member of the committee, Mangus Mittag-Leffler, was a strong supporter of women in science. So, he wrote Pierre to tell him of this pending injustice. Pierre responded in such a way that the committee felt compelled to include Marie. The 1903 Nobel Prize for Physics was awarded to both Curies and Becquerel. The citation was written was written very cleverly so that the Curies received the prize “in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel.”
The 1903 citation did not mention the chemical separation of radium. That deliberate omission opened the way for Marie to receive the Nobel Prize in Chemistry in 1911 “in recognition of her services to the advancement of chemistry by the discovery of the elements radium and polonium, by the isolation of radium and the study of the nature and compounds of this remarkable element.” Thus Marie Sklodowska Curie became the first woman to receive a Nobel Prize and the first person to receive two prizes. (The second woman to receive a Nobel Prize was Marie and Pierre’s daughter Irene.)
The lack of caution in handling radioactive material greatly affected both of the Curies. They were too ill to attend the Nobel ceremony in 1903. The illness came and went, so in the summer of 1905, they felt well enough to travel to Stockholm where Pierre gave a Nobel lecture. However, he was soon feeling bad again.
On April 19, 1906, Pierre was walking in the rain. Apparently, he was not paying attention to traffic and walked in front of a horse-drawn wagon. He was killed instantly when the rear wheel of the wagon struck his head. Some historians believe that radiation poisoning contributed to his weakness. Thus, he was unable to avoid the fatal blow once he had accidently stepped in front of the wagon.
Marie was devastated and took a long time to recover from Pierre’s death. Eventually she did continue the research that she and Pierre had shared.
Part of the War Effort
In addition to her research, she provided a critical service during World War I. She learned that soldiers’ lives could be save if only X-ray equipment were available at or near the front. To address this need, she developed portable X-ray units.
For the first one, she received a gift from the Union of the Women of France. With this money, she purchased a Renault car and had it converted into an ambulance. She then had X-ray equipment installed in the car. She personally drove this vehicle to locations near the front lines, frequently accompanied by her daughter Irene. She obtained about 20 other vehicles and outfitted them in a similar way. The X-rays provided by the equipment in these vehicles, called “little Curies,” have been credited with saving the lives of thousands of wounded soldiers.
Marie’s work in radioactivity and its medical applications continued after the war. You can find many books, web pages, and videos about her. One of the most famous is a biography by her second daughter, Eve. If you are interested in more information, just search. A good short biography of both Curies is on the Nobel Prize website.
While the Curies were undertaking their work, a couple of other major contributions to our understanding of matter were being developed. The beginnings of quantum physics were under way as well as the use of radioactivity to probe deeply into the atom. In the next post, I will take a look at probing the atom and the building of a model of the nuclear atom. After that, we will back up a little in time and consider some of the early ideas in quantum physics.
Dean Zollman is university distinguished professor of physics at Kansas State University where he has been a faculty member for more than 40 years. During his career he has received four major awards — the American Association of Physics Teachers’ Oersted Medal (2014), the National Science Foundation Director’s Award for Distinguished Teacher Scholars (2004), the Carnegie Foundation for the Advancement of Teaching Doctoral University Professor of the Year (1996), and AAPT’s Robert A. Millikan Medal (1995). His present research concentrates on the teaching and learning of physics and on science teacher preparation.