A two hundred meter length of 100/140 micron Graded Index (GRIN) optical fiber was exposed to a beam of relativistic Fe ions, with an energy spectrum similar to that of galactic cosmic2rays between 10 and 600MeV /amu, for 9.1 sec with a flux 2E7 ion /cm sec, for a total fluence of 2E6 ion /cm .No change in the optical characteristics of the fiber was noted in a measurement with a noise floor of less than 0.5dB /km. The major source of noise was due to vibration of the fiber.This exposure represents the total fluence of highly energetic Fe ions that would be expected to accumulate in space over a 100 year period of time due to the naturally occurring galactic cosmic rays GCR.The measurements were performed in early 1987.

Monitoring aging aircraft for hidden corrosion is a significant problem for both military and civilian aircraft. Under a Wright Laboratory sponsored program, Boeing Defense & Space Group is investigating three novel methods for detecting and monitoring hidden corrosion: 1) atmospheric neutron radiography, 2) 14 MeV neutron activation analysis and 3) fiber optic corrosion sensors. Atmospheric neutron radiography utilizes the presence of neutrons in the upper atmosphere as a source for interrogation of the aircraft structure. Passive track-etch neutron detectors, which have been previously placed on the aircraft, are evaluated during maintenance checks to assess the presence of corrosion. Neutrons generated by an accelerator are used via activation analysis to assess the presence of distinctive elements in corrosion products, particularly oxygen. By using fast (14 MeV) neutrons for the activation, portable, high intensity sources can be employed for field testing of aircraft. The third novel method uses fiber optics as part of a smart structure technology for corrosion detection and monitoring. Fiber optic corrosion sensors are placed in the aircraft at locations known to be susceptible to corrosion. Periodic monitoring of the sensors is used to alert maintenance personnel to the presence and degree of corrosion at specific locations on the aircraft. During the atmospheric neutron experimentation, we identified a fourth method referred to as secondary emission radiography (SER). This paper discusses the development of these methods. INTRODUCTIONThe two primary damage mechanisms that limit the life of metallic aircraft structure are fatigue and corrosion. Corrosion has been found to be a problem that increases with age, particularly when the original design lifetime is exceeded. Experience has shown that corrosion can be managed but not eliminated, so detecting corrosion will remain an issue no matter how effective corrosion prevention programs become. A particularly costly concern is corrosion in hidden or inaccessible areas. In general, by the time corrosion is detected without disassembly, the damage is so extensive that massive repairs are required. Conversely, disassembly of these regions to inspect for the corrosion is time consuming and costly, particularly when there is no corrosion present. Further, disassembly often results in additional damage to the aircrafL Corrosion is the destructive attack of a metal by chemical or electrochemical reaction with its environment.The primary metals (aluminum and steel) in older aircraft are both prone to corrosion. In the presence of an appropriate electrolyte, these metals will convert, by an electrochemical process, to oxides and/or hydroxides. Being electrochemical, corrosion may be accelerated by either the presence of two different metals, such as a steel rivet in an aluminum hole, or by the passage of an electrical current, such as near the point of attachment of a grounding strap which is carrying current. Fortuitously, upon exposure to air, aluminum quickly form...