- 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.
April 2016 