Nuclear science is a broad discipline dealing with the origins and properties of nuclear radiations, their detection and measurement, and their applications in basic and applied research, in diagnostic and therapeutic medicine, and in technology and engineering. Nuclear science began with Röntgen’s (1895) discovery of x-rays and Becquerel’s (1896) discovery of radioactivity. Both of these discoveries were made by experiment. The detection and measurement of nuclear radiations preceded the development of nuclear models to explain the phenomenon. The experiments described in this manual are fundamental to understanding the properties of nuclear radiations and their detection and measurement.
Nuclear radiations are the manifestations of energy associated with atomic or nuclear changes. The Rutherford-Bohr model of the atom is adequate for describing most of these changes, such as the increase or decrease in atomic number associated with negatron or positron emission, the decrease in atomic number and mass number associated with alpha emission, x-ray emission associated with electron capture, and Auger electron emission.
The Rutherford-Bohr or planetary model describes the atoms as a central nucleus containing protons and neutrons and orbiting electrons traveling in fairly well defined pathways around the nucleus. In the neutral atom, the number of electrons equals the number of protons.
The atom shown in Figure 1 represents carbon. The nucleus of the carbon atom contains six protons. Six electrons orbit the nucleus of the carbon atom. Each element has a unique name and a unique one- or two-letter symbol. The element carbon has been given the symbol C. The symbol for the element calcium is Ca, and the symbol for the element cadmium is Cd. Each element is placed in the periodic table (Figure 2) according to the number of protons in its nucleus. The number of protons in the nucleus of the atom is the atomic number of the element. The atomic number of carbon is 6 because its nucleus contains six protons. Currently, the periodic table contains some 115 elements.