Review of 252Cf neutron radiography at McClellan Air Force Base

The Maneuverable Neutron Radiography System (MNRS) at McClellan Air Force Base, Sacramento, California, utilized two independent neutron source modules to perform inspections of fully assembled and partially disassembled aircraft. Each source module, or moderator collimator shield (MCS), carried up to 50 mg of 252Cf and was designed to efficiently thermalize the neutrons and form a high-quality radiography beam. One MCS was mounted on an overhead robotic mast and was normally used with one of two different electronic imaging systems. This overhead system was used for inspection of the horizontal and vertical flight surfaces of the assembled aircraft. The other MCS, of fundamentally the same design, rode on a set of traveling rails running beneath the aircraft and was normally used only with film. This underside system inspected the walls of the engine bays with the engines removed. The MNRS operated from 1989 to 1994; it was decommissioned in 1998. During that period, more than one hundred aircraft were inspected. The aircraft types varied, but all the military services participated in the program. The most comprehensive study was done on the US Air Force F-15 aircraft. The ability to perform the two complementary inspections (i.e., maneuverable X-ray and maneuverable neutron radiography) on the same components under the same conditions (i.e., physically and environmentally) provided an ideal opportunity to evaluate the relative merits of the two systems. The MNRS performed in an outstanding manner and should lead the way for further military and commercial development in the area of nondestructive inspection