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Saturday, April 16, 2016

Reading List: Obsessive Genius

Goldsmith, Barbara. Obsessive Genius. New York: W. W. Norton, 2005. ISBN 978-0-393-32748-9.
Maria Salomea Skłodowska was born in 1867 in Warsaw, Poland, then part of the Russian Empire. She was the fifth and last child born to her parents, Władysław and Bronisława Skłodowski, both teachers. Both parents were members of a lower class of the aristocracy called the Szlachta, but had lost their wealth through involvement in the Polish nationalist movement opposed to Russian rule. They retained the love of learning characteristic of their class, and had independently obtained teaching appointments before meeting and marrying. Their children were raised in an intellectual atmosphere, with their father reading books aloud to them in Polish, Russian, French, German, and English, all languages in which he was fluent.

During Maria's childhood, her father lost his teaching position after his anti-Russian sentiments and activities were discovered, and supported himself by operating a boarding school for boys from the provinces. In cramped and less than sanitary conditions, one of the boarders infected two of the children with typhus: Marie's sister Zofia died. Three years later, her mother, Bronisława, died of tuberculosis. Maria experienced her first episode of depression, a malady which would haunt her throughout life.

Despite having graduated from secondary school with honours, Marie and her sister Bronisława could not pursue their education in Poland, as the universities did not admit women. Marie made an agreement with her older sister: she would support Bronisława's medical education at the Sorbonne in Paris in return for her supporting Maria's studies there after she graduated and entered practice. Maria worked as a governess, supporting Bronisława. Finally, in 1891, she was able to travel to Paris and enroll in the Sorbonne. On the registration forms, she signed her name as “Marie”.

One of just 23 women among the two thousand enrolled in the School of Sciences, Marie studied physics, chemistry, and mathematics under an eminent faculty including luminaries such as Henri Poincaré. In 1893, she earned her degree in physics, one of only two women to graduate with a science degree that year, and in 1894 obtained a second degree in mathematics, ranking second in her class.

Finances remained tight, and Marie was delighted when one of her professors, Gabriel Lippman, arranged for her to receive a grant to study the magnetic properties of different kinds of steel. She set to work on the project but made little progress because the equipment she was using in Lippman's laboratory was cumbersome and insensitive. A friend recommended she contact a little-known physicist who was an expert on magnetism in metals and had developed instruments for precision measurements. Marie arranged to meet Pierre Curie to discuss her work.

Pierre was working at the School of Industrial Physics and Chemistry of the City of Paris (EPCI), an institution much less prestigious than the Sorbonne, in a laboratory which the visiting Lord Kelvin described as “a cubbyhole between the hallway and a student laboratory”. Still, he had major achievements to his credit. In 1880, with his brother Jacques, he had discovered the phenomenon of piezoelectricity, the interaction between electricity and mechanical stress in solids. Now the foundation of many technologies, the Curies used piezoelectricity to build an electrometer much more sensitive than previous instruments. His doctoral dissertation on the effects of temperature on the magnetism of metals introduced the concept of a critical temperature, different for each metal or alloy, at which permanent magnetism is lost. This is now called the Curie temperature.

When Pierre and Marie first met, they were immediately taken with one another: both from families of modest means, largely self-educated, and fascinated by scientific investigation. Pierre rapidly fell in love and was determined to marry Marie, but she, having been rejected in an earlier relationship in Poland, was hesitant and still planned to return to Warsaw. Pierre eventually persuaded Marie, and the two were married in July 1895. Marie was given a small laboratory space in the EPCI building to pursue work on magnetism, and henceforth the Curies would be a scientific team.

In the final years of the nineteenth century “rays” were all the rage. In 1896, Wilhelm Conrad Röntgen discovered penetrating radiation produced by accelerating electrons (which he called “cathode rays”, as the electron would not be discovered until the following year) into a metal target. He called them “X-rays”, using “X” as the symbol for the unknown. The same year, Henri Becquerel discovered that a sample of uranium salts could expose a photographic plate even if the plate were wrapped in a black cloth. In 1897 he published six papers on these “Becquerel rays”. Both discoveries were completely accidental.

The year that Marie was ready to begin her doctoral research, 65 percent of the papers presented at the Academy of Sciences in Paris were devoted to X-rays. Pierre suggested that Marie investigate the Becquerel rays produced by uranium, as they had been largely neglected by other scientists. She began a series of experiments using an electrometer designed by Pierre. The instrument was sensitive but exasperating to operate: Lord Rayleigh later wrote that electrometers were “designed by the devil”. Patiently, Marie measured the rays produced by uranium and then moved on to test samples of other elements. Among them, only thorium produced detectable rays.

She then made a puzzling observation. Uranium was produced from an ore called pitchblende. When she tested a sample of the residue of pitchblende from which all of the uranium had been extracted, she measured rays four times as energetic as those from pure uranium. She inferred that there must be a substance, perhaps a new chemical element, remaining in the pitchblende residue which was more radioactive than uranium. She then tested a thorium ore and found it also to produce rays more energetic than pure thorium. Perhaps here was yet another element to be discovered.

In March 1898, Marie wrote a paper in which she presented her measurements of the uranium and thorium ores, introduced the word “radioactivity” to describe the phenomenon, put forth the hypothesis that one or more undiscovered elements were responsible, suggested that radioactivity could be used to discover new elements, and, based upon her observations that radioactivity was unaffected by chemical processes, that it must be “an atomic property”. Neither Pierre nor Marie were members of the Academy of Sciences; Marie's former professor, Gabriel Lippman, presented the paper on her behalf.

It was one thing to hypothesise the existence of a new element or elements, and entirely another to isolate the element and determine its properties. Ore, like pitchblende, is a mix of chemical compounds. Starting with ore from which the uranium had been extracted, the Curies undertook a process to chemically separate these components. Those found to be radioactive were then distilled to increase their purity. With each distillation their activity increased. They finally found two of these fractions contained all the radioactivity. One was chemically similar to barium, while the other resembled bismuth. Measuring the properties of the fractions indicated they must be a mixture of the new radioactive elements and other, lighter elements.

To isolate the new elements, a process called “fractionation” was undertaken. When crystals form from a solution, the lighter elements tend to crystallise first. By repeating this process, the heavier elements could slowly be concentrated. With each fractionation the radioactivity increased. Working with the fraction which behaved like bismuth, the Curies eventually purified it to be 400 times as radioactive as uranium. No spectrum of the new element could yet be determined, but the Curies were sufficiently confident in the presence of a new element to publish a paper in July 1898 announcing the discovery and naming the new element “polonium” after Marie's native Poland. In December, working with the fraction which chemically resembled barium, they produced a sample 900 times as radioactive as uranium. This time a clear novel spectral line was found, and at the end of December 1898 they announced the discovery of a second new element, which they named “radium”.

Two new elements had been discovered, with evidence sufficiently persuasive that their existence was generally accepted. But the existing samples were known to be impure. The physical and chemical properties of the new elements, allowing their places in the periodic table to be determined, would require removal of the impurities and isolation of pure samples. The same process of fractionation could be used, but since it quickly became clear that the new radioactive elements were a tiny fraction of the samples in which they had been discovered, it would be necessary to scale up the process to something closer to an industrial scale. (The sample in which radium had been identified was 900 times more radioactive than uranium. Pure radium was eventually found to be ten million times as radioactive as uranium.)

Pierre learned that the residue from extracting uranium from pitchblende was dumped in a forest near the uranium mine. He arranged to have the Austrian government donate the material at no cost, and found the funds to ship it to the laboratory in Paris. Now, instead of test tubes, they were working with tons of material. Pierre convinced a chemical company to perform the first round of purification, persuading them that other researchers would be eager to buy the resulting material. Eventually, they delivered twenty kilogram lots of material to the Curies which were fifty times as radioactive as uranium. From there the Curie laboratory took over the subsequent purification. After four years, processing ten tons of pitchblende residue, hundreds of tons of rinsing water, thousands of fractionations, one tenth of a gram of radium chloride was produced that was sufficiently pure to measure its properties. In July 1902 Marie announced the isolation of radium and placed it on the periodic table as element 88.

In June of 1903, Marie defended her doctoral thesis, becoming the first woman in France to obtain a doctorate in science. With the discovery of radium, the source of the enormous energy it and other radioactive elements released became a major focus of research. Ernest Rutherford argued that radioactivity was a process of “atomic disintegration” in which one element was spontaneously transmuting to another. The Curies originally doubted this hypothesis, but after repeating the experiments of Rutherford, accepted his conclusion as correct.

In 1903, the Nobel Prize for Physics was shared by Marie and Pierre Curie and Henri Becquerel, awarded for the discovery of radioactivity. The discovery of radium and polonium was not mentioned. Marie embarked on the isolation of polonium, and within two years produced a sample sufficiently pure to place it as element 84 on the periodic table with an estimate of its half-life of 140 days (the modern value is 138.4 days). Polonium is about 5000 times as radioactive as radium. Polonium and radium found in nature are the products of decay of primordial uranium and thorium. Their half-lives are so short (radium's is 1600 years) that any present at the Earth's formation has long since decayed.

After the announcement of the discovery of radium and the Nobel prize, the Curies, and especially Marie, became celebrities. Awards, honorary doctorates, and memberships in the academies of science of several countries followed, along with financial support and the laboratory facilities they had lacked while performing the work which won them such acclaim. Radium became a popular fad, hailed as a cure for cancer and other diseases, a fountain of youth, and promoted by quacks promising all kinds of benefits from the nostrums they peddled, some of which, to the detriment of their customers, actually contained minute quantities of radium.

Tragedy struck in April 1906 when Pierre was killed in a traffic accident: run over on a Paris street in a heavy rainstorm by a wagon pulled by two horses. Marie was inconsolable, immersing herself in laboratory work and neglecting her two young daughters. Her spells of depression returned. She continued to explore the properties of radium and polonium and worked to establish a standard unit to measure radioactive decay, calibrated by radium. (This unit is now called the curie, but is no longer defined based upon radium and has been replaced by the becquerel, which is simply an inverse second.) Marie Curie was not interested or involved in the work to determine the structure of the atom and its nucleus or the development of quantum theory. The Curie laboratory continued to grow, but focused on production of radium and its applications in medicine and industry. Lise Meitner applied for a job at the laboratory and was rejected. Meitner later said she believed that Marie thought her a potential rival to Curie's daughter Irène. Meitner joined the Kaiser Wilhelm Institute in Berlin and went on to co-discover nuclear fission. The only two chemical elements named in whole or part for women are curium (element 96, named for both Pierre and Marie) and meitnerium (element 109).

In 1910, after three years of work with André-Louis Debierne, Marie managed to produce a sample of metallic radium, allowing a definitive measurement of its properties. In 1911, she won a second Nobel prize, unshared, in chemistry, for the isolation of radium and polonium. At the moment of triumph, news broke of a messy affair she had been carrying on with Pierre's successor at the EPCI, Paul Langevin, a married man. The popular press, who had hailed Marie as a towering figure of French science, went after her with bared fangs and mockery, and she went into seclusion under an assumed name.

During World War I, she invented and promoted the use of mobile field X-ray units (called “Les Petites Curies”) and won acceptance for women to operate them near the front, with her daughter Irène assisting in the effort. After the war, her reputation largely rehabilitated, Marie not only accepted but contributed to the growth of the Curie myth, seeing it as a way to fund her laboratory and research. Irène took the lead at the laboratory.

As co-discoverer of the phenomenon of radioactivity and two chemical elements, Curie's achievements were well recognised. She was the first woman to win a Nobel prize, the first person to win two Nobel prizes, and the only person so far to win Nobel prizes in two different sciences. (The third woman to win a Nobel prize was her daughter, Irène Joliot-Curie, for the discovery of artificial radioactivity.) She was the first woman to be appointed a full professor at the Sorbonne.

Marie Curie died of anæmia in 1934, probably brought on by exposure to radiation over her career. She took few precautions, and her papers and personal effects remain radioactive to this day. Her legacy is one of dedication and indefatigable persistence in achieving the goals she set for herself, regardless of the scientific and technical challenges and the barriers women faced at the time. She demonstrated that pure persistence, coupled with a brilliant intellect, can overcome formidable obstacles.

Posted at April 16, 2016 20:46