1898 - the Radioactive Year
With such apparatus ready at hand, Marie could accurately measure the energy output of various compounds containing uranium, including pitchblende. Initially, Curie found that the amount of energy given off by a particular compound corresponded directly to the amount of uranium present in substance, leading Curie to conclude that the energy came directly from the uranium atoms, rather than from some chemical reaction occuring between uranium and other elements in the compound. When she examined the pitchblende, however, Curie found that it demonstrated significantly higher levels of emanation than could be accounted for by the ore’s uranium content. In a paper presented on April 12, 1898, Curie mentioned her hypothesis that the ore must contain trace quantities of other, as-yet-unknown elements. That same month, Marie, joined now by her husband, began attempting to isolate the source of that extra energy. By July, the pair published a joint paper announcing the discovery of a new and far more radioactive element, which they named "polonium," after Marie's home country. Five months later, on the day after Christmas, the Curies announced the existence of a second new element, "radium," and coined a term, “radioactive,” to describe elements that spontaneously produced radiation. Although the Curies had enough evidence to claim the existence of the two new elements, they did not yet have pure samples of the substances. In order to fully verify their discoveries, the couple set out to purify radium and polonium samples from the pitchblende where they had first discovered the elements.