ABSTRACT
WHAT IS MEANT BY RADIATION?1.1 The word radiation was used until about 1900 to describe electromagnetic waves. Around the turn of the century, electrons, X-rays, and natural radioactivity were discovered and were included under the umbrella of the term radiation. The newly discovered radiation showed characteristics of particles, in contrast to the electromagnetic radiation, which was treated as a wave. In the 1920s, DeBroglie developed his theory of the duality of matter, which was soon proved correct by electron diffraction experiments, and the distinction between particles and waves ceased to be important. Today, radiation refers to the whole electromagnetic spectrum as well as to all the atomic and subatomic particles that have been discovered.
