The beginning of this book was university lecture notes and training material for process engineers. Although it now is a lot more comprehensive, it has been our intention to maintain a mixed academic and industrial approach to the various subjects. Our motivation for writing this book has been the need for a text covering the full range from the underlying physics to the process applications of radioisotope gauges. We could not deal with all subjects in detail; however, we have included references to many excellent books and articles where further details can be found
