Marie's early research in Paris centered on correlating the chemical compositions of various steels with their magnetic properties. An important consequence of this work was her meeting with Pierre Curie, himself a long-time researcher on magnetism.
After publishing the results of her research, Marie turned to considering topics for her doctoral research. Following the recent work of Henri Becquerel, who reported on the spontaneous radiation emitted by uranium compounds, Marie Curie decided to focus her research on further investigation of this new phenomenon
To measure the weak electric currents caused by the radiation and obtain comparable data, Curie used the electrometer invented by her husband, Pierre, and his brother, Jacques, rather than rely photographic plate intensities. The emissions were found to be constant and independent of physical state or purity; radiation strength depended only on the amount of uranium in the sample. This led to Marie Curie's first hypothesis that the radiation originated in the elemental uranium in the sample.
This fundamental observation set the stage for subsequent discoveries on atomic structure and the intrinsic power of the atom. Whereas up to that time the atom was considered to be the smallest, indivisible particle existing in matter, the radiation observed would indicate that the "indivisible" atom was now subject to decomposition to smaller components.
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