Low energy p-Be nuclear reactions for depth-profiling Be in alloys

Beryllium distributions within the first micron of the surface of nickel- or copper-based alloys were investigated with a 300 keV proton probe utilizing low energy nuclear reactions. In the case of the Ni specimens, segregation of Be was induced by point defect flows to the surface of the specimen during Ni-ion bombardment at elevated temperatures. The nuclear reactions used for the detection of Be are 9Be(p, d)8Be with a Q value of 0.56 MeV and 9Be(p, α)6Li with a Q value of 2.12 MeV. The deuteron and alpha groups are simultaneously observable using a standard surface barrier detector. Observations were made at a 1500 scattering angle with and without a 2.5 μm mylar filter in front of the detector. This filter was found necessary for observing the deuteron yields since pulse pile-up from backscattered protons would otherwise mask the deuteron signal. The alpha group may be observed with or without the filter depending on whether counting statistics or energy resolution are the more important constraints. Significant Be segregation toward the surface was observed in specimens after irradiation at 6250C to 23 dpa with 3.2 MeV Ni ions. Concentrations of Be were nearly doubled within 500 A of the surface and a region depleted of Be extended below the surface layer to a depth of about 3000 A. These results are in reasonable agreement with predictions from computer calculations of alloy segregation induced by defect fluxes to free surfaces during irradiation at elevated temperatures. (Auth.)