In 1896, Henri Becquerel was studying uranium when he discovered a new type of radiation that could pass through metal. His research got the attention of physicist Marie Curie, who began to study these uranium rays.

She soon made a revolutionary discovery when she determined that the ability to radiate did not depend on the arrangement of the atoms in a molecule, but on the interior of the atom.



The Curies in their laboratory around 1904

Marie was joined by her physicist husband Pierre to study uraninite, then known as pitchblende, a uranium-rich mineral and ore. The pair removed uranium and were left with a radioactive material they determined should be two new elements, radium and polonium.

They first discovered polonium, named for Marie’s homeland Poland, in July 1898. In documenting their work they wrote, “We thus believe that the substance that we have extracted from pitchblende contains a metal never known before, akin to bismuth in its analytic properties.” The substance was about 300 times more strongly active than uranium. In this paper, the pair also used the term radioactivity for the first time.

Later that year, on December 21, 1898, the Curies found radioactive compounds similar to barium compounds that became a new element they named radium because of the way it emitted energy in rays. They measured radium’s intensity at around 3,000 times uranium.

The discovery of radium allowed for radiotherapy and nuclear medicine, which changed the treatment of cancer and other diseases. As early as 1899, it was reported that a malignant tumor of the skin was cured by radioactive source application.

The detrimental effects of radiation were not immediately known, and the research took its toll on the Curies’ health. Use of radium in everyday life, including its use in luminous paint to create watches that would glow in the dark, led to the discovery of radiation poisoning. Marie died in 1934 from aplastic anemia, likely caused by her exposure to radiation. The pair’s laboratory notes are still radioactive and have to be stored in lead boxes, and Marie’s coffin was lined with lead.

In 1903, Marie and Pierre Curie shared the Nobel Prize in Physics with Becquerel for ”the extraordinary services they have rendered by their joint researches on the radiation phenomena.”The common historical unit for radioactivity is the curie, in honor of the pair. The becquerel is now the SI derived unit of radioactivity.

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Editor’s note: This article was originally posted on December 21, 2017 and edited on December 21, 2018.