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Bequerel and Two Curies
Pierre and Marie Curie
By the time he met his future wife, Pierre Curie (1859 - 1906) had already established a name for himself as a scientist. In 1880, he and his brother had discovered piezoelectricity whereby physical pressure applied to a crystal resulted in the creation of an electric potential. He had also made important investigations into the phenomenon of magnetism including the identification of a temperature, the curie point, above which a material's magnetic properties disappear. However, shortly after his marriage to Marie Sklodowska (1867 - 1934) in 1895, Pierre subjugated his research interests to hers. Together, they began investigating the phenomenon of radioactivity recently discovered in uranium ore (although the phenomenon was discovered by Henri Becquerel, the term radioactivity was coined by Marie). After chemical extraction of uranium from the ore, Marie noted the residual material to be more "active" than the uranium itself. She concluded that the ore contained, in addition to uranium, new elements that were also radioactive. This led to the discoveries of the elements polonium and radium. Four more years of processing tons of ore under oppressive conditions were required to isolate enough of each element to determine its chemical properties. For their work on radioactivity, the Curies were awarded the 1903 Nobel Prize in physics. Tragically, Pierre was killed three years later in an accident while crossing a street in a rainstorm. Pierre's teaching position at the Sorbonne was given to Marie. Never before had a woman taught there in its 650 year history! Her first lecture began with the very sentence her husband had used to finish his last. In his honor, the 1910 Radiology Congress chose the curie as the basic unit of radioactivity: the quantity of radon in equilibrium with one gram of radium. A year later, Marie was awarded the Nobel Prize in Chemistry for her discoveries of radium and polonium, thus becoming the first person to receive two Nobel Prizes. For the remainder of her life she tirelessly investigated and promoted the use of radium as a treatment for cancer. Marie Curie died July 4, 1934, overtaken by pernicious anemia no doubt caused by years of overwork and radiation exposure.
Becquerel (1852-1908) was born into a family of scientists. His grandfather
had made important contributions in the field of electrochemistry while
his father had investigated the phenomena of fluorescence and phosphorescence.
Becquerel not only inherited their interest in science, he also inherited
the minerals and compounds studied by his father. And so, upon learning
how Wilhelm Röntgen discovered x-rays by observing the fluorescence they
produced, Becquerel had a ready source of fluorescent materials with which
to pursue his own investigations of these mysterious rays. The material
Becquerel chose was a double sulfate of uranium and potassium which he
exposed to sunlight and placed on photographic plates wrapped in black
paper. When developed, the plates revealed an image of the uranium crystals.
Becquerel concluded "that the phosphorescent substance in question emits
radiation which penetrates paper opaque to light.", i.e. he believed that
the sun's energy was being absorbed by the uranium which then emitted
x-rays. Further investigation, on the 26th and 27 of February, was delayed
because the skies over Paris were overcast and the uranium-covered plates
Becquerel intended to expose to the sun were returned to a drawer. On
the first of March, he developed the photographic plates expecting only
faint images to appear. To his surprise, the images were clear and strong.
This meant that the uranium emitted radiation without an external source
of energy such as the sun. Becquerel had discovered radioactivity, the
spontaneous emission of radiation by a material. Later, Becquerel demonstrated
that the radiation emitted by uranium shared certain characteristics with
x-rays but, unlike the latter, could be deflected by a magnetic field
and therefore must consist of charged particles. For his discovery of
radioactivity, Becquerel was awarded the 1903 Nobel Prize for physics.
In 1994, the Health Physics Society produced a calendar for the centennial commemoration of the discovery of X-rays (1885) and Radioactivity (1886). This calendar contained profiles of some of the pioneers in the field of Health Physics and Radiation Science. The above text is taken from this calendar. A special thanks to Paul Frame of ORAU and the other members of the HPS Historical Committee for their work on this calendar.
For more on Pioneers in Health Physics, all of the profiles are available at this MSU web site.