1.   Soon after, Marie Sklodowska-Curie made the crucial discovery and isolation of radium, a radioactive element.

2.   This law states that the number of atoms of a radioactive element is halved after a given amount of time has elapsed.

3.   Thus the disintegration of the radioactive elements is a heat source that has persisted for billions of years.

4.   Also in the box is a device that contains a small amount of a radioactive element.

5.   And third, the disintegration of radioactive elements released particles and radiation, which were absorbed by the surrounding rock, heating it.

6.   At the core of each nuclear weapon is a small, hollow ball of plutonium, a highly radioactive element.

7.   A. Helium is chiefly the product of the decay of radioactive elements and is found associated with ancient deposits of natural gas.

8.   Both the federal government and your state require your water supplier to test regularly for contaminants, including bacteria, radioactive elements and certain toxic chemicals.

9.   But Fisher, who uses the radioactive elements to develop new drugs, said isotopes are sometimes difficult to obtain.

10.   Federal guidelines do not require testing within a particular time frame, so this radioactive element decayed before it could normally be detected.