Fast neutron and γ-ray backscatter radiography for the characterization of corrosion-born defects in oil pipelines

In this research, a combined fast-neutron/gamma-ray backscatter imaging technique is described. The aim of this work is to understand corrosion defects in pipelines by measuring differences in the scattered radiation flux, generated when different steel thicknesses are irradiated by a neutron and gamma-ray focused beam. A californium-252 radiation source is used to produce fast neutron and rays, exploiting its spontaneous fission. This mixed radiation field is collimated and directed towards the steel samples. Backscattered neutrons and rays are measured as a function of the steel thickness using 4 liquid organic scintillation detectors linked to a real-time, pulse-shape discrimination system, which separates and retains the neutron and gamma-ray event data. In this paper, we describe how, using a single radiation source and detection system, it is possible to perform and combine two complementary imaging modalities. This research is validated by an MCNP6 computer simulation study. The backscatter imaging system developed for this research and the experimental results of the measurements carried out using the National Physical Laboratory neutron low-scatter facility are also presented in this paper.