Alice Siemons, age 12, of Mississauga, Ontario, Canada, for her question:

How does uranium differ from radium?

Uranium is a heavy radioactive element that spontaneously breaks down into a series of lighter elements. At each stage of the process, larger atoms lose a particle or particles and emit a nuclear radiation. The loss of nuclear particles changes the nature of an atom and it becomes an atom of something else. Radium is one of the elements created in the radioactive decay of uranium. It is a smaller atom than uranium and proceeds to decay at a faster rate. Its radioactivity is estimated to be a million times more dynamic than that of its parent, uranium.

The atomic number of uranium, giving its nuclear protons, is 92; that of radium is 88. Hence, uranium decays through several stages to reach radium. During the natural decay process, various smaller elements remain in the uranium mineral. From 200 tons of the best uranium ore, it is possible to extract about one ounce of dynamic radium. The radium proceeds to decay into smaller atoms of radon, emitting nuclear radiation as more radium atoms are formed in the uranium ore.