Observation of Tritium Distribution in Pure Vanadium and V-5 mol%Fe Alloy by Tritium Radioluminography

Tritium radioluminography was applied to pure vanadium and V-5 mol%Fe alloy to observe the tritium distribution and to evaluate the local tritium concentration in them. It was demonstrated that the tritium distribution at a microscopic area in the specimens was quantitatively and graphically displayed. In the pure vanadium specimen, the local tritium concentration was about three times different depending on the crystal orientation of the grains. The tritium radioactivity of the grains with (001) and (111) orientation are 1 Bq/mm² and 0.4 Bq/mm², respectively. These values correspond to the tritium concentration of 15 mol ppb and 6 mol ppb. The difference of the local tritium concentration was attributed to the variety of the morphology of precipitated hydride depending on the crystal orientation of the grains. For the radioactivity recorded in the imaging plate, the component of the X-rays generated from tritium in the specimen was only 2%, i.e., most of the intensity was attributed to the β-rays. In the V-Fe alloy specimen, it was shown that the tritium distribution correlates with iron segregation formed during solidification after the arc melting. The cross sectional observation showed that the local tritium concentration in equilibrium distribution depends on the local iron concentration in the specimen. The local tritium concentration gradually decreases from 115 mol ppb to 70 mol ppb as the iron concentration at the iron segregated region increases from 3 mol% to 4.5 mol%.