Marie carried on their research and was appointed to fill Pierre's position at the Sorbonne, thus becoming the first woman in France to achieve professorial rank. In 1906, Pierre was killed in a traffic accident. It was not until 1932 that James Chadwick discovered the existence of a particle in the. Isolating pure samples of these elements was exhausting work for Marie it took four years of back-breaking effort to extract 1 decigram of radium chloride from several tons of raw ore. Yet the protons did not account for all of the atomic weight of an atom.

In 1898, they announced the discovery of two new elements, radium and polonium. This discovery is perhaps her most important scientific contribution. She discovered that radioactivity does not depend on how atoms are arranged into molecules, but rather that it originates within the atoms themselves. British physicist James Chadwick, building upon Rutherfords experiments, discovered that atomic nuclei contain neutrally charged particles-neutrons-in. In an article he wrote for the Manchester Literary and Philosophical Society in 1803, Dalton created the first chart of atomic weights. They discovered that thorium also emitted radiation, and further, that the amount of radiation depended upon the amount of element present in the compound.

Marie and Pierre Curie :In 1898, they announced the discovery of two new elements, radium and polonium.

When was the atomic theory discovered