Spurred by the discovery that a substance containing uranium emitted radiation, Marie Curie began studying radioactivity in 1897. She first tested gold and copper for radiation but found none. She then tested pitchblende, a mineral that was known to contain uranium, and discovered that it was more radioactive than uranium. Acting on radiating and nonradiating elements, she was unable to postulate a mechanism by which to explain radiation.
It is now known that radiation occurs when certain isotopes (atoms of the same element that differ slightly in their atomic structure) decay, and that emission rates are not constant but decrease very slowly with time. Some critics have recently faulted Curie for not reaching these conclusions herself, but it would have in a process that takes billions of years, are present in nature exclusively in radioactive form.
Furthermore, we must recall that in Curie’s time the nature of the atom itself was still being debated. Physicists believed that matter could not be divided indefinitely but instead would eventually be reduced to its indivisible components. Chemists, on the other hand, observing that chemical reactions took place as if matter was concerned with the question of whether or not such indivisible atoms actually existed.
As a physicist, Curie conjectured that radiating substances might lose mass in the form of atoms, but this idea is very different from the explanation eventually arrived at. It was not until the 1930s that advances in quantum mechanics overthrew the earlier understanding of the atom and showed that radiation occurs because recognize that it was Curie’s investigation of radiation that paved the way for the later breakthroughs.
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