Chapter 30 Measurements Employing Nuclear Techniques D. Aliaga Kelly and W. Boyes 30.1 IntroductIon There are two important aspects of using nuclear techniques in industry which must be provided for before any work takes place. These are: 1. Compliance with the many legal requirements when using or intending to use radioactive sources; 2. Adequate health physics procedures and instruments to ensure that the user is meeting the legal requirements The legal requirements cover the proposed use of the radioactive source, the way in which it is delivered to the Before considering these applications in detail we dis- cuss some general points that are relevant to all or most of them. one of the outstanding advantages of radioisotopes is the way in which their radiation can pass through the walls of a container to a suitable detector without requiring any contact with the substance being measured. This means that dangerous liquids or gases may be effectively controlled or measured without risk of leakage, either of the substance itself out from the container or of external contamination to the substance inside. Thus in the chemical industry many highly toxic materials may be measured and controlled com-