 Neutron penetration into materials makes californium useful in detection instruments such as fuel rod scanners; neutron radiography of aircraft and weapons components to detect corrosion, bad welds, cracks and trapped moisture; and in portable metal detectors. Neutron moisture gauges use californium-252 to find water and petroleum layers in oil wells, as a portable neutron source for gold and silver prospecting for on-the-spot analysis, and to detect ground water movement. The major uses of californium-252 in 1982 were, in order of use, reactor start-up (48.3 %), fuel rod scanning (25.3 %), and activation analysis (19.4 %). By 1994 most californium-252 was used in neutron radiography (77.4 %), with fuel rod scanning (12.1 %) and reactor start-up (6.9 %) as important but distant secondary uses.
