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Helium released from beryllium irradiated at 600 and 750 C was measured and related to a macro-diffusion coefficient, D. The value of D at 600 C was 6.8 x 10-14 and at 750 C was 1.13 x 10-9 cm2Vsec. The magnitude of the macro-diffusion coefficient at 750 C agrees with that predicted for gas diffusion in beryllium, but that at 600 C agrees better with self-diffusion coefficient. The activation energy, G, for release of helium in the equation D = D0 exp - G/kT is then 5 ev, which corresponds to the activation energy for re-solution processes. The recoil mechanism for helium release was considered and shown to be small where appreciable gas was released from the specimens. The microstructure of the beryllium showed larger gas bubble formation in the grain boundaries than within the grains. The compression yield strength of the beryllium irradiated at 1 × 1021 neutrons (n)/cm2 E > 1 Mev at these temperatures increased only slightly, and the ultimate compression strength decreased, although appreciable plastic deformation was sustained in the compression testing.
helium bubbles, beryllium, irradiation, radiation effects, gas diffusion, diffusion, compressive strength, activation energy, microstructure, grain boundaries, irradiation hardening
Beeston, J. M.
Chief, Idaho Nuclear Corp., Idaho Falls, Idaho