Radium and polonium
Throughout her life one of Marie's main inspirations was Henri Becquerel. She worked towards further extended his studies in uranium. She found out that uranium rays remain constant no matter the condition or form they are in. To continue, her ideas first formed the field of atomic physics. Marie was also the one to first use the word 'radioactivity'. She worked toward explaining radioactivity, and did this by separating various substances. For example, while some substances may dissolve in acid, others will remain whole. After separating the substances, Marie collected only the remaining substance to test for the amount of radioactive elements in it. In early 1898, she discovered one substance that contained barium was strongly radioactive. This element was named polonium, after Marie's home town of Poland. Later in December of 1898, a different substance with barium was discovered by Marie and her husband and they named it radium. Although these two elements have completely different chemical properties, they are both have high levels of radioactivity. Her efforts also later led to the invention of the x-ray.