In industrial processes, it is useful to have a range of non-intrusive techniques that can effectively ‘look’ through vessel and pipe walls to measure process parameters and to identify plant problems. Sealed radioactive sources, specifically those that emit gamma radiation and neutron particles, are ideally suited for these purposes and have been used for industrial applications for many years. This publication describes several available techniques with sealed radioactive sources, by showing examples of their use in industrial applications and by demonstrating how they can be used to improve process efficiency and to save money. The focus of the publication corresponds to two major techniques with sealed radioactive sources: gamma scanning and neutron backscattering, which are largely applied for diagnosis and troubleshooting in processing vessels, columns and in pipes.