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A novel technique is described for injecting helium into materials of arbitrary type and composition during mixed-spectrum reactor irradiations. This method is a variation of the isotopic alloying technique developed recently, wherein nickel is required as an alloy constituent in the specimens of interest. In the present method no nickel is added to the specimens, so that no changes are introduced in the physical metallurgy. The specimens are interposed between injector foils containing nickel. Helium is generated as a particles of energy 4.7 MeV in the two-step reaction 58Ni(n,γ)59Ni(n,α)59Fe within the injector foils. A fraction of the helium is injected directly into the adjacent specimens to depths of tens of micrometers for typical structural materials. Both the nickel content of the foils and the relative abundances of the isotopes of nickel can be varied to control the helium injection rate over a very wide range, covering helium concentrations of interest in basic studies and technological applications. Mathematical expressions to describe both helium buildup with dose and helium spatial profiles are presented. Results are shown for sample calculations applicable to the quantitative design of experiments in aluminum, copper, and vanadium.
radiation effects, helium, isotopic alloying, microstructure, flux spectrum, helium implantation, transmutation products
Group leader, Oak Ridge National Laboratory, Oak Ridge, TN
Professor, Arizona State University, Tempe, AZ