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Radioactive Tracer Methods
Involves irradiating the entire part by exposing it to thermal neutrons in a nuclear reactor to obtain gamma emitting radionuclides, then installing the activated parts in the test engine. Once these parts are re-installed in the test engine, gamma rays emitted from radionuclides of the irradiated wear particles serve as detectable tracers as the particles circulate through the lubrication system after being abraded from the moving parts as the engine is operated in a variety of speed and load regimes. Measuring radiation levels associated with these particles using a gamma ray spectrometer provides a direct measure of the mass of wear particles present in the oil. When compared to calibrations or other baseline values, or to activity at a particular time, these measurements give the direct amount of wear suffered by the parts during a given period. Thus, wear can be measured in real-time without disassembling the engine for inspection.
Surface or Thin Layer Activation
Involves irradiating a thin layer of atoms in the surface of the target part, perhaps 10 to 150 micrometers deep, by bombarding it with a high energy beam of charged particles. The purpose is to create gamma-ray emitting radionuclides in the surface layer for use as detectable tracers for wear abraded particles or as markers for non-abraded materials. Wear is measured as diminished emissions from the parts, or as increased emissions from abraded particles suspended in lubrication oil.
Involves replacing some of the hydrogen atoms in lube oil with radioactive tritium atoms (3H) through catalytic exchange, and measuring by means of liquid scintillation counting rather than the scintillation detectors used to measure gamma radiation in the above methods. Tritium tracing is a tool for measuring engine oil consumption accurately over short periods of operation.
Published in the Spring 1998 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Joe Fohn.