In 1895, a German physicist named Wilhelm Roentgen fortuitously discovered X-rays while experimenting with evacuated glass tubes through which an electric current was passed. Roentgen discovered he could take a picture of the bones in his hand with the mysterious new rays. Henri Becquerel of France discovered natural radioactivity a year later. The momentous discoveries of these physicists led to a rapid advancement of scientific knowledge about radiation and radioactivity, as well as to many practical uses. Types of Radiation For purposes of radiation safety only radiation with the capability to cause ionization is of concern.
Ionization occurs when electrons are dislodged from a neutral atom.
When this happens an atom becomes positively charged and some energy is transferred. Ionization is the process by which radiation affects the human body and by which it can be detected as well. The main properties of each type of radiation are briefly discussed below. Alpha particles consist of two protons and two neutrons and carry a positive charge. They are emitted with high energy from the nucleus of heavy elements during radioactive decay, but lose energy rapidly in passing through material.