Bulk Activation

For bulk-activation testing, components are neutron irradiated in a nuclear reactor and installed in a test engine. As irradiated particles abrade from these components during engine operation, specific radionuclides serve as detectable tracers in the lubricant.

Southwest Research Institute (SwRI) measures radiation from these particles using gamma ray spectroscopy. The radiation detected is proportional to the mass of the abraded material in the circulating fluids. Multiple radionuclides can be measured simultaneously, allowing wear from multiple parts or surfaces to be measured during a single test.

The white paper, Overview of the Bulk-Activation RATT^® Method, has more details about BA.

	Using bulk activation radioactive tracer methods, SwRI measures transient piston ring wear associated with speed and load changes.

 

 

 

 

 

 

 

 

The Vehicle Systems Research Department staff study the impact of dust ingestion on engine wear using upstream dust particle sizing and radioactive tracer wear measurement and analysis.

Surface-Layer or Thin-Layer Activation

	Radioactive tracer wear testing can be applied to virtually any metal part that provides suitable radionuclides when irradiated. In addition to engine components, transmission gears and hydraulic pump parts are ideal candidates.

Surface-layer or thin-layer activation is especially useful for measuring wear in large parts that are not amenable to bulk activation or for measuring wear in a specific area, such as on a cam lobe, at the cylinder liner reversal point, or at a contact spot on a fuel injector.

Using SLA/TLA techniques, components are bombarded with a high-energy beam of charged particles to activate a thin layer of atoms on the component surface in the area of interest. Wear is measured by directly monitoring the decrease in the component's radioactivity or the increase in radioactivity as irradiated wear particles accumulate in a circulation loop.

Nuclear Recoil Implantation

In special cases, such as when no suitable metallurgy is available or a non-metal part is of interest (for example, plastics), when a shallow depth profile is needed to increase sensitivity, or when direct irradiation might damage the parent material, radioactive tracers are obtained by nuclear recoil implantation. In this method of irradiation, a high energy ion beam is used to create recoiling radioactive atoms from a target that are then kinetically implanted into the part of interest.

Nuclear recoil radioactive tracer implantation technology was coupled with a multi-station hip wear simulator to measure minute amounts of wear in orthopedic implants (nonmetallic, UHMWPE acetabular cups, with Be-7 implanted radionuclides) under representative conditions of use. Real-time wear was measured using a recirculating fluid loop that continuously transported Bovine calf serum between the hip simulator and a shielded radiation detector.

Wear in the orthopedic implants was monitored for nearly 2 million cycles, and the onset of detectable wear was noted at 36,000 cycles. The mass loss equivalent was in the 10-microgram range, which can not be measured gravimetrically. Typically, 5 million cycles are required to measure wear using conventional weight-loss methods. In this testing, the fluid was replaced every 250,000 cycles to facilitate other measurements. As can be seen, wear was detected early in every cycle, and trended upward as expected. The real-time data can provide much needed information about possible immune system triggering events.

For more information about our radioactive tracer techniques, or how you can contract with SwRI, please contact Doug Eberle at deberle@swri.org or (210) 522-5260. 

radioactivetracer.swri.org