The use of contrast agents to enhance crack detection via neutron radiography

Contrast agents have been used in a wide variety of neutron radiographic an d radioscopic examinations. Useful contrast agents range from simple hydrog enous materials such as water and oil to exotic compounds such as gadoliniu m chelates. The properties of the contrast agents also vary widely. Conside rations such as the ability to penetrate into cracks, the ability to be rem oved, the neutron cross-section, or the neutron attenuation mechanism, ofte n steer the investigator to select a particular contrast agent. We have qua ntified the behavior of the following substances as contrast agents: an aqu eous liquid penetrant, a solvent-based liquid penetrant, water, a GdCl3 aqu eous solution, and a solution of gadolinium beta-diketonate (2,2,6,6-tetram ethyl-3,5-heptanedione) (TMHD) dissolved in acetone and methylene chloride. The experimental tests were carried out using wedge-shaped gaps that simul ated cracks, and in actual cracks in Inconel tubing. The experimental resul ts showed that an aqueous solution of GdCl3 used with a wetting agent provi ded the best performance, but was difficult to remove completely from the c rack. (C) 1998 Elsevier Science Ltd. All rights reserved.