Nuclear radiation cannot be detected by any of the five human senses directly. For example, radiation from naturally-occurring sources such as carbon-14 or potassium-40 is present in the environment around us at all times. But without special instruments to detect its presence, humans are totally unaware of its existence. It was necessary, therefore, to develop instruments for the detection of radiation as soon as the existence of that radiation was recognized.

Detection devices can be classified in a variety of ways. For example, some instruments are counters. They record the presence and the number of particles present in a situation. The Geiger counter is an example of such a device.

Other instruments record the track of a particle. A cloud chamber, for example, allows one to take a picture of a particle's movement through an electrical and/or magnetic field. The picture provides information about the...