Wear Rates in Automotive Engines by Liquid Scintillation Counting of Fe⁵⁵

A new radiotracer technique for determining wear rates of selected automotive engine parts is described and demonstrated for piston rings. The technique uses Fe⁵⁵ instead of Fe⁵⁹ as the radiotracer. A liquid scintillation method for counting Fe⁵⁵ is necessary since it decays by electron capture and emits only the Mn characteristic X-ray of 5.9 keV. A simple method for extracting the wear particles from the engine oil and getting the iron into the liquid scintillation mixture is described. Counting yields of 8 to 9% are obtained by the method. The Fe⁵⁵ technique of wear measurement does not directly compete with the existing Fe⁵⁹ technique since slightly lower sensitivity and longer sample preparation is required. However, the much longer half-life (2.6 years as compared to 45 days) and the lower radiation energy (5.9 keV as compared to over 1 MeV) allows the Fe⁵⁵ technique to be used for long-term wear studies, for double tracer studies, and for studies of large engine parts.