Radium was not to enrich anyone. Radium is an element. It belongs to all people
Maria Skłodowska-Curie
The history of nuclear chemistry and physics as well as brachytherapy began on February
1896 in Paris. After the discovery of X-rays in 1895 by the German physicist Wilhelm
Conrad Röntgen (1845-1923), the French physicist Antoine Henri Becquerel (1852-1908)
fortuitously discovered that minerals of uranium spontaneously emitted rays very similar
to X-rays. It was a milestone in the history of nuclear physics and chemistry as well
as modern medicine [1]. However, the development of brachytherapy is directly related
to the genius and systematic work of Maria Skłodowska-Curie (1867-1934) and her husband
Pierre Curie (1859-1906) [2]. Subsequently, when Irène (1897-1956) and Frédéric Joliot-Curie
(1900-1958) discovered artificial radioactivity in 1934, they opened a new path to
brachytherapy [3,4].
On December 28th 1895, Röntgen (Photo 1) published the results of the research in
Ueber eine neue Art von Strahlen (On a new type of ray) [5]. It was the beginning
of a scientific revolution. Very quickly the whole world of science learned about
the unusual discovery of a German. This discovery was so important that Wilhelm Conrad
Röntgen became the first Nobel Prize winner in physics in 1901. The justification
states that he received the prize “in recognition of the extraordinary services he
has rendered by the discovery of the remarkable rays subsequently named after him”.
Photo 1
Wilhelm Conrad Röntgen, b.d., Wellcome Collection (public domain)
In January 1896 at the session of the Academy of Sciences in Paris, Henri Poincaré
(1854-1912) suggested that X-rays may be similar to fluorescence. Fascinated by this
information, Becquerel (Photo 2) began a series of studies on uranium salts. He exposed
them to sunlight and then he applied salts to photographic plates that became black.
At the end of February 1896, it was cloudy and rainy in Paris. Becquerel could not
expose the uranium salts in solar radiation. He placed a photographic plate and unexposed
salt in a drawer. After a few days he decided to develop a photographic plate. To
his surprise, it was blackened. Uranium salts emit radiation without solar radiation.
Becquerel identified natural radioactivity in his photographic plate in contact with
uranium crystals. He himself published seven papers on radioactivity in 1896, and
two in 1897 and none the year after. After the discovery of polonium and radium in
1898 by the Curies, Becquerel wrote only four papers in 1899. Becquerel’s observations
showed that uranium and its compounds in crystallized form dissolved or molten spontaneously
emitted radiation. He also noticed that this radiation blacked the photographic plates,
ionized the air, penetrated through nontransparent bodies, and it was similar to visible
light, i.e. it was reflected, refracted, and polarized; therefore, uranium radiation
was similar to electromagnetic radiation [1]. As it turned out, his last observation
was false and resulted from misinterpretation of the experiments. It was the great
discovery which Maria Skłodowska-Curie would later name radioactivity.
Photo 2
Antoine-Henri Becquerel, 1908, photo: P. Nadar, Smithsonian Institution Libraries
(public domain)
At the end of 1897 Maria Skłodowska-Curie (Photo 3) chose as the subject of her doctoral
thesis the investigation of uranium rays. Because Becquerel investigation only two
properties of uranium rays – the effect on photographic plates and ionization – Maria
focused on a second measurable property. She first repeated the Becquerel experiments,
and then instead of the photographic plates used by him she used a very sensitive
electrometer with piezoelectric quartz. Thanks to systematic and very exact measurements
Maria Skłodowska-Curie stated that radiation of uranium depends on the amount of uranium
and is proportional to it. It was a milestone in the study of radioactivity. Maria
was the first to state that radiation is the atomic property of uranium! Although
similar studies were carried out in Naples by Emilio Villari (1836-1904), he probably
did not even think of similar conclusions [6]. Then, Maria collected many elements
in the free state or as compounds and rapidly came to the conclusion that, besides
uranium, also thorium emits radiation. She made this discovery regardless of the German
physics Gerhard Carl Schmidt (1865-1949). Of all the elements Madame Curie tested,
only two – uranium and thorium – gave off invisible ionizing rays, and Maria Skłodowska-Curie
named the new phenomenon as “radio-activity” in 1898. These rays became generally
known as “Becquerel rays”, a term first used by Maria Skłodowska-Curie in the same
year. At the same time, she proved that the emission of radiation by thorium is quantitatively
different from the emission of uranium. No one else carried out such research. Her
research results became the basis for her doctoral dissertation in 1903 [7]. It is
worth noting that Pierre Curie (Photo 4) also participated in these works, and (as
he thought) temporarily left his studies on crystals. Another important observation
of Maria Skłodowska-Curie was the fact that the emission of radiation of some minerals
containing uranium: pitchblende, chalcolite or autunite are much stronger than it
would appear from the content of uranium in their composition. Because Maria knew
the chemical composition of chalcolite, she found that only uranium was a radioactive
element in this mineral. She put forward a bold hypothesis that this mineral must
contain a new, unknown chemical element. On July 28th 1898 the Curies wrote: “Certain
minerals containing uranium and thorium (pitchblende, chalcolite, uranite) are very
active from the point of view of the emission of Becquerel rays. In a preceding communication,
one of us showed that their activity was even greater than that of uranium and thorium,
and stated the opinion that this effect was due to some other very active substance
contained in a small quantity in these minerals” [8]. The first step to confirm it
was the chemical synthesis of chalcolite. Maria had proved that synthetic chalcolite
emits weaker radiation, i.e. what would be expected from the uranium content of this
mineral (Photo 5). It was indisputable experimental evidence for the existence of
a new chemical element [9]. Together, the Curies using their radioactive indicator
method determined the radiation of the new element. It radiated four hundred times
stronger than uranium [2]. In the Proceedings of the Academy for July 1898 they wrote:
“We believe the substance we have extracted from pitchblende contains a metal not
yet observed, related to bismuth by its analytical properties. If the existence of
this new metal is confirmed we propose to call it polonium, from the name of the original
country of one of us” [8].
Photo 3
Marie Skłodowska-Curie, Birmingham, 1913, Musée Curie (coll. ACJC)
Photo 4
Pierre Curie, 1905, Musée Curie (coll. ACJC)
Photo 5
Pierre and Marie Curie with Monsieur Petit (lab assistant) in their laboratory, the
“hangar of discovery”, at the School of Physical and Industrial Chemistry of the city
of Paris, about 1898, Musée Curie (coll. ACJC)
The Curies did not have to wait too long for another success. In November they conducted
a series of experiments, thanks to which they received a very radioactive product.
With the participation of Gustav Bémont (1857-1932), they managed to obtain a sample
containing barium with radioactivity nine hundred times greater than uranium! On December
26th, 1898, together with assistant Bémont, they announced that they had discovered
a second chemical element – radium. They wrote: “The various reasons we have just
enumerated lead us to believe that the new radioactive substance contains a new element
to which we propose to give the name of RADIUM. The new radioactive substance certainly
contains a very strong proportion of barium; in spite of that its radioactivity is
considerable. The radioactivity of radium therefore must be enormous” [8]. Polonium
and radium were observed by the Curies due to high radioactivity. Now scientists needed
additional evidence to confirm that both elements existed. Eugène Demarçay (1852-1904),
a specialist in the field of emission spectroscopy, took spectra of newly discovered
elements. Demarçay heated polonium and radium-containing substances to a gaseous state
in a torch flame, and then analyzed the spectra that arose as a result of the light
they split. Curies had proof of the existence of radium in the form of an emission
spectrum that showed a weak but distinct purple line at 381.48 nm corresponding to
this element [2]. Unfortunately, the concentration of polonium in the sample was too
weak to observe the emission line. The three radioactive elements uranium, thorium
and radium belong to the long-lived elements, so that scientists hardly observed any
decrease in their radioactivity. In turn, polonium is one of the short-lived elements
for which radioactive activity decreases with time. Maria Skłodowska-Curie hypothesized
that the radioactive activity is constant for a given element. So there was doubt
whether polonium was not a bismuth, whose activity was raised by the radium. In addition,
the presence of only bismuth lines in the emission spectrum was in favor of this hypothesis.
On the other hand, Maria concluded that the amount of polonium in the sample could
be so small that its line was not noticed. Building on this bold idea, Maria Skłodowska-Curie,
together with Pierre Curie, founded the field of radiochemistry [10,11,12].
It is noteworthy that one of the greatest discoveries in human history was made in
very primitive conditions. The Curies’ “laboratory” was an old shed (a former dissecting
room) (Photos 6-8). The German chemist Wilhelm Ostwald (1853-1932) visited the Curies
to see how they worked. He later wrote: “At my earnest request, I was shown the laboratory
where radium had been discovered shortly before… It was a cross between a stable and
a potato shed, and if I had not seen the worktable and items of chemical apparatus,
I would have thought that I had been played a practical joke” [2]. In her autobiography
Maria wrote: “Yet it was in this miserable old shed that we passed the best and happiest
years of our life, devoting our entire days to our work. Often I had to prepare our
lunch in the shed, so as not to interrupt some particularly important operation. Sometimes
I had to spend a whole day mixing a boiling mass with a heavy iron rod nearly as large
as myself. I would be broken with fatigue at the day’s end. On other days, however,
the work would be a most minute and delicate fractional crystallization, in the effort
to concentrate the radium. I was then annoyed by the floating dust of iron and coal
from which I could not protect my precious products. But I shall never be able to
express the joy of the untroubled quietness of this atmosphere of research and excitement
of actual progress with the confident hope of still better results. The feeling of
discouragement that sometimes came after some unsuccessful toil did not last long
and gave way to renewed activity. We had happy moments devoted to a quiet discussion
of our work, walking around our shed. One of our joys was to go into our workroom
at night; we then perceived on all sides the feebly luminous silhouettes of the bottles
or capsules containing our products. It was really a lovely sight and one always new
to us. The glowing tubes looked like faint, fairy lights” [13].
Photo 6
Interior of the “shed” laboratory of Pierre and Marie Curie, at the School of Physics
and Industrial Chemistry of the city of Paris, about 1898, Musée Curie (coll. ACJC)
Photos 7 and 8
Pierre and Marie Curie in the laboratory, called the “hangar of the discovery”, at
the School of Physics and Industrial Chemistry, around December 1903, Musée Curie
(coll. ACJC)
The natural consequence of Maria and Pierre Curie’s discoveries was to enrich Mendeleev’s
periodic table of elements with another element. In 1899 the Curies’ friend Andre-Louis
Debierne (1874–1949) (Photo 9), had found another new active substance in pitchblende.
He named it actinium, probably from actinic, the era’s term for radiation that darkened
a photographic plate. Debierne thought actinium resembled thorium chemically. He wondered
whether thorium’s radioactivity was really caused by traces of actinium.
Photo 9
André Debierne around 1940, Musée Curie (coll. ACJC)
Research on new radioactive elements was extremely interesting, intriguing, innovative
and gave a lot of hope for the application of their properties in medicine. Studies
of Pierre Curie were described by Maria in her biography. She wrote: “Finally, I cannot
pass in silence, because of their various repercussions, the experiments connected
with the physiological effects of radium. In order to test the results that had just
been announced by F. Giesel, Pierre Curie voluntarily exposed his arm to the action
of radium for several hours. This resulted in a lesion resembling a burn, which developed
progressively and required several months to heal. Henri Becquerel had by accident
a similar burn as a result of carrying in his vest pocket a glass tube containing
radium salt. He came to tell us of this evil effect of radium, exclaiming in a manner
at once delighted and annoyed: “I love it, but I owe it a grudge!”. Since he realized
the interest in these physiological effects of radium, Pierre Curie undertook, in
collaboration with physicians, the investigations to which I have just referred, submitting
animals to the action of radium emanation. These studies formed the point of departure
in radium therapy. The first attempts at treatment with radium were made with products
loaned by Pierre Curie, and had as their object the cure of lupus and other skin lesions.
Thus radium therapy, an important branch of medicine, and frequently designated as
Curietherapie, was born in France, and was developed first through the investigations
of French physicians (Danlos, Oudin, Wickham, Dominici, Cheron, Degrais, and others)”
[13]. Maria and Pierre Curie started a new type of chemistry – radiation chemistry
– and a new therapy, which would later be called curietherapy [14]. Curie also noted
that inactive substances near radioactive bodies become briefly radioactive. This
phenomenon is called radioactivity excitation.
The whole world was crazy about radium and radioactivity. Maria Skłodowska-Curie was
hailed as the Radium Madonna. Curie received many prestigious awards for their work:
Plante, Lacaze, Gegner, Osiris, Davy’s Medal. This discovery was so important to science
as well as medicine that Becquerel and Maria and Pierre Curie became the Nobel Prize
winners in physics in 1903. The justification states that Becquerel received a prize
“in recognition of the extraordinary services he has rendered by his discovery of
spontaneous radioactivity”, and the Curies “in recognition of the extraordinary services
they have rendered by their joint research on the radiation phenomena discovered by
Professor Henri Becquerel” [15,16,17].
After Maria and Pierre Curie first discovered the radioactive elements polonium and
radium, Maria continued to investigate their properties (Pierre Curie died in a traffic
accident in 1906). In 1910 she successfully obtained radium as a pure metal. It was
evidence that radium is a chemical element. Maria Skłodowska-Curie also studied and
described the properties of the radioactive elements and their compounds. For this
work, she received the second Nobel Prize in 1911 in chemistry. The justification
states that she received the prize “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”.
In my opinion, besides a great experimenter, Maria Skłodowska-Curie was a great visionary
of science, who was years ahead of her time. On 14th June 1900 at the Sorbonne Maria
Curie developed her hypothesis of possibility of the transformation of atoms. She
suggested: “The material radioactive theory fully considers phenomena noted so far.
However, if we are to accept this theory, we will have to concede that radioactive
matter is not a normal chemical state. In this case, the atom is not unchanging and
indivisible, since its particles are radiated out. Radioactive matter is subject to
chemical transformation, and that very change is the source of energy in radiation;
but it is not a usual chemical transformation, for here the atom itself is subject
to change. It is apparent after all that if radioactivity is a result of transformation
of matter, then the atom must transform, as radioactivity is an atomic phenomenon”
[1].