covered until well into the 20th century. But right around the turn of this century, scientists observed that certain atoms undergo mysterious transformations. For example, atoms of radium (a rare metallic element) turn into atoms of radon (a rare gaseous element).

    Equally as surprising, the radium atom emits a tiny particle, called an alpha particle, when the change takes place. This alpha particle consists of two neutrons and two protons. It is identical to the nucleus of a helium atom.

    We now know that this transformation is an example of radioactive decay, a process whereby one atom breaks apart to form one or more smaller atoms.

     Radium atoms decay into radon atoms and alpha particles spontaneously. In other words, every so often an atom in a chunk of radium metal will decide, on its own, to break apart. There are many other atoms that will break  apart  spontaneously.  Scientists  call  these  substances   naturally   radioactive.

    When an atom breaks apart, the decay process also gives off energy. In certain circumstances, it is possible to capture this energy in the form of heat, then use the heat to generate electricity. This is the principle of operation of all the nuclear-powered electricity generating plants that are at work today.

Atomic Cousins

There’s one more nuclear term we want to define here: isotope. A bit earlier we said that different atoms have different nuclei and different numbers of electrons. An atom of oxygen, for example, has eight protons and eight neutrons in its nucleus and eight electrons whirling

around the nucleus. Broadly speaking, it is the number of protons and electrons that determine the character of an atom and, consequently, the character of the chemical element that the atoms form.

    Sometimes, a specific chemical element will contain atoms of slightly differing form. The numbers of protons and electrons will be the same, but the number of neutrons will not. These slightly different atoms are called isotopes.

There are, for example, isotopes of oxygen that contain seven and nine neutrons, instead of eight.

    Isotopes  play  an  important  role  in  nuclear  energy. Specifically, an isotope of uranium called U-235 was the first material used to create a nuclear chain reaction.

    If you have followed what we’ve said so far, you are ready to learn more about nuclear energy by performing the experiments that follow. Good luck.