The Prize:
The Nobel Prize in Physics to Antoine Henri Becquerel for “his discovery of spontaneous radioactivity” and to Marie and Pierre Curie for their work “on the radiation phenomena discovered by Professor Henri Becquerel.”
The Science:
Most scientific discoveries are the result of small steps and the contributions of different scientists. Many of these steps are serendipitous and unexpected. This is true of the initial discovery of radioactivity.
In 1895, German physicist Wilhelm Röntgen discovered the X-ray (called Röntgen rays in many other languages), for which he won the first Nobel Prize in Physics in 1901. Intrigued by the results of Röntgen, Henri Becquerel set out to further expand on the understanding of X-rays. Although he went looking for X-rays, he ended up discovering radioactivity.
Becquerel was interested in determining if phosphorescence (a natural light emission that some minerals display after being exposed to sunlight) involved X-rays, too. Becquerel studied uranium, a mineral known to phosphoresce after some time in the sun. He placed the uranium salts next to a photographic plate to test for the emission of X-rays. Unexpectedly, the plate displayed the image of the uranium salt even before the uranium had been exposed to sunlight. This indicated that the uranium salts were emitting radiation that was independent of their phosphorescence, and required no external energy source.
Becquerel went on to show that the “rays” from uranium that caused the photographic plate to cloud could be deflected by either electric or magnetic fields, a property that set them apart from X-rays. This radiation became known as Becquerel radiation, now better known as the much-maligned radioactivity. The SI (Système International) unit for radioactivity is named for him.
After discovering radioactivity and performing the first important experiments, Becquerel moved on to other work. It was at this time that Marie Curie was looking for a topic for her doctoral thesis.
Marie Curie had come to Paris from her native Poland looking to further her studies in science. She studied math and physics and planned to return to Poland to take up work as a teacher. These plans changed when she met and married Pierre Curie, a man as excited about science as she. After marrying, Marie decided to further her career with a doctorate. Hearing of Becquerel’s results, she chose to study the radiation emitted by uranium.
As part of her doctoral thesis, Marie showed that thorium, another chemical element, gives off the same radiation as uranium and that the amount of radiation both elements emit does not depend on the molecular structure of the mineral that uranium and thorium were in complex with, but instead on the amount of uranium or thorium in the sample. This suggested that radioactivity is linked to the atom itself and not to its molecular arrangement, a revolutionary discovery.
Marie’s next step was to methodically test all the natural ores that she could find for radioactivity. Combing through samples from geological museums, Marie found that pitchblende (a “waste byproduct” of mineral mining) had four to five times more radioactivity than uranium. Although Marie didn’t know it, pitchblende contains uranium, radium, and polonium, all high sources of radioactivity. Marie (correctly) hypothesized that pitchblende must contain an unknown element that gave off more radioactivity then uranium alone.
Pierre Curie stopped his own research at this point to join Marie in her work. Together they proved Marie’s hypothesis and discovered the elements radium (from the Latin word for ray) and polonium (for Poland). They worked long, arduous hours, in a rudimentary lab space (some described their first lab as a “miserable old shed”), exposing themselves to massive amounts of radioactivity. In addition to their long hours in the lab, Marie and Pierre also had to keep up teaching duties at the Sorbonne.
In addition to the chemistry of radioactivity, the Curies were also interested in the effects of radioactivity on the human body. Pierre carried out medical experiments on himself showing that radium, when applied to the skin, left a scar. He suggested radium as a therapeutic for cancer, what we now know as radiation therapy. During their lifetime, Marie and Pierre displayed many signs of radiation sickness: fatigue, cracked skin, weakness. Pierre died in 1906 in a traffic accident, but Marie continued her work on radioactivity as a professor in her own laboratory. During the First World War, she was instrumental in making X-ray machines available for treating wounded soldiers. She died of aplastic anemia in 1934, a disease associated with exposure to radioactivity.
Marie and Pierre’s daughter Irène Joliot-Curie pursued a career in science, also focusing on radioactivity. She shared the 1935 Nobel Prize in Chemistry with her husband Frédéric Joliot “in recognition of their synthesis of new
radioactive elements.”
The Significance:
In 1903, Becquerel and the Curies were jointly awarded the Nobel Prize in Physics. Marie Curie alone won the 1911 Nobel Prize in Chemistry for her discovery and characterization of radium and polonium. She is the only woman to have won the Nobel Prize twice, the first female professor and laboratory head at the Sorbonne University, and one of the first two women to have received her PhD in Europe—a lot of firsts for one person.
During her lifetime, Marie faced many challenges. Even after winning the 1903 Nobel Prize and a recommendation from leading physicists, she was denied entry into France’s l’Académie des Sciences, based on a combination of anti-semitism (her maiden name may have been of Jewish origin), sexism, and nationalism (Marie was a Polish emigre). She was also at the centre of an unsubstantiated sex-scandal that clouded the announcement of her second
Nobel Prize.
Today, the darkness has faded. Marie and Pierre’s bodies rest in the French Pantheon in Paris, a great honour bestowed on France’s most illustrious citizens. As well, many scientific awards today are named for Marie, as well as a major Cancer Care Network and Research Institute in the United Kingdom, in part for her independent spirit and scientific perseverance.
