The last half of the twentieth century was a time in which tremendous advances in science and technology revolutionized our entire way of life. Many new technologies were invented and developed in this time period from basic laboratory research to widespread commercial application. Communication technology, genetic engineering, personal computers, medical diagnostics and therapy, bioengineering, and material sciences are just a few areas that were greatly affected.
Nuclear science and engineering is another technology that has been transformed in less than fifty years from laboratory research into practical applications encountered in almost all aspects of our modern technological society. Nuclear power, from the first experimental reactor built in 1942, has become an important source of electrical power in many countries. Nuclear technology is widely used in medical imaging, diagnostics, and therapy. Agriculture and many other industries make wide use of radioisotopes and other radiation sources. Finally, nuclear applications are found in a wide range of research endeavors such as archaeology, biology, physics, chemistry, cosmology, and, of course, engineering.
The discipline of nuclear science and engineering is concerned with quantifying how various types of radiation interact with matter and how these interactions affect matter. In this book, we will describe sources of radiation, radiation interactions, and the results of such interactions. As the word “nuclear” suggests, we will address phenomena at a microscopic level, involving individual atoms and their constituent nuclei and electrons. The radiation we are concerned with is generally very penetrating and arises from physical processes at the atomic level.
However, before we begin our exploration of the atomic world, it is necessary to introduce some basic fundamental atomic concepts, properties, nomenclature, and units used to quantify the phenomena we will encounter. Such is the purpose of this introductory chapter.
With only a few exceptions, units used in nuclear science and engineering are those defined by the SI system of metric units. This system is known as the “International System of Units” with the abbreviation SI taken from the French “Le Système International d’Unitès.” In this system, there are four categories of units: (1) base units of which there are seven, (2) derived units which are combinations of the base units, (3) supplementary units, and (4) temporary units which are in widespread use for special applications. These units are shown in Table 1.1
. To accommodate very small and large quantities, the SI units and their symbols are scaled by using the SI prefixes given in Table 1.2
The SI system of units and their four categories.
Source: NBS Special Publication 330, National Bureau of Standards, Washington, DC, 1977.
There are several units outside the SI which are in wide use. These include the time units day (d), hour (h), and minute (min); the liter (L or ℓ
); plane angle degree (°), minute (′), and second (″); and, of great use in nuclear and atomic physics, the electron volt (eV) and the atomic mass unit (u). Conversion factors to convert some non-SI units to their SI equivalent are given in Table 1.3
Finally it should be noted that correct use of SI units requires some “grammar” on how to properly combine different units and the prefixes. A summary of the SI grammar is presented in Table 1.4