In situ ERDA measurements of hydrogen isotope concentrations in palladium at atmospheric pressure

Abstract

In situ elastic recoil detection analysis (ERDA) measurements in gases at atmospheric pressure have been carried out using 15MeV 4He ion beams. The beams are extracted through a molybdenum foil having a thickness of 5μm. The maximum depth of analysis is about 4μm for the palladium hydride and palladium deuteride (PdHx and PdDx, x=0.7–0.8) samples. The temperature of the samples rises stepwise from room temperature to 180°C. ERDA spectra are obtained every 2min. Hydrogen and deuterium in the samples are discharged in the temperature range of 120–140°C in a vacuum. Decrease in the hydrogen concentration in the PdHx sample heated in a vacuum follows a first order in the value of x and an apparent activation energy of discharge of hydrogen is 1.05eV. On the other hand, the hydrogen and deuterium concentrations decrease at about 80°C in air. No isotope effects are observed in both a vacuum and air. The temperature at which the hydrogen concentration decreases in helium gas is almost the same as that in a vacuum. It indicates that hydrogen and deuterium atoms are discharged by chemical reactions with air and that there are no effects of cooling of the thermocouple by convection of air.