Precision dilatometry of Nb, Ta, and Lu tritides

Applying buoyancy dilatometry at room temperature to NbT/sub 0.0253/ and strain-gauge dilatometry at room temperature and 78 K to TaT/sub 0.0744/ and LuT/sub 0.15/, respectively, we have measured the swelling of these tritides due to the transmutation of T to 3He in the first two years after T charging. For all three tritides almost linear swelling is found, indicating approximately constant 3He densities in bubbles. The corresponding values for the volume requirement of a 3He atom in a bubble are around 8 A3. Associated pressure values are derived with the aid of an equation of state for 3He adapted to recent high-pressure x-ray-diffraction measurements on solid 4He. With increasing 3He concentration the pressure seems to converge to about 0.2 of the shear modulus of the metal, in accordance with recent theoretical results concerning the threshold pressure for dislocation-loop punching by bubbles