Energy from Atoms - Nuclear Power - page 3

To produce nuclear energy, certain types of atoms are
needed. Usually, they are atoms of the substances uranium
or plutonium . Uranium and plutonium are both elements ,
which are basic substances that make up all matter. There are
approximately 115 elements known to scientists today.
Every element has a specii c number of protons in the
nuclei of its atoms. The number of neutrons may vary. The
nuclei of uranium and plutonium have many protons and
neutrons. Uranium has 92 protons, while plutonium has 94
protons. Some elements have much smaller nuclei. Oxygen, for
example, has only eight protons, carbon has six protons, and
hydrogen has just one proton!

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Radioactivity

The nuclei of the atoms of some substances are said to be
unstable. That means that every now and then, they give off
radiation . The nature of the radiation depends on the situation
and the type of substance involved. Substances that give off
radiation are said to be radioactive. The radiation they give off—
their radioactivity—may be harmful to living things. The elements
uranium and plutonium are radioactive.
When an element gives off certain types of radiation, it
changes into a different element. Scientists call this process
decay. When a radioactive element decays, the new element
may or may not also be radioactive. If it is not radioactive, the
new element is said to be stable. It will not easily change into
something else.