In 1895 German physicist Wilhelm Conrad Röntgen began a program of study on the behavior of electricity when subjected to certain variables. To his surprise, he discovered that electricity in a vacuum produced rays that caused material to fluoresce and, under certain conditions, even illuminate the human skeleton. He called these mysterious emanations X-rays. In 1896 French physicist Antoine Henri Becquerel began his own experiments on Röntgen’s X-rays.1 He discovered that certain substances, such as uranyl sulfate, emitted rays with properties similar, though not identical, to those discovered by Röntgen.
Meanwhile, in 1897 British researcher J. J. Thomson found that atoms were not indivisible as previously thought, but instead contained even smaller particles which he called corpuscles. He suggested that these particles moved within the positively charged atomic body, explaining the atom’s neutral charge.2 After further refining his theory, he received the 1906 Nobel Prize in Physics.
In 1898 Gerhard Schmidt of Germany began to investigate the question of whether or not other elements naturally emitted Becquerel rays. He soon found that only thorium produced them. Two months later, Marie Curie, a scientist in Paris, made the same discovery.3
In experimenting with pitchblende, a uranium-rich mineral, Curie found much higher concentrations of radiation than uranium was known to emit. In her search to uncover the cause she undertook the difficult task of isolating and identifying the components of pitchblende. Through this process, she discovered two new elements which she named polonium and radium.