The behaviour of helium gas in irradiated copper-boron alloys

The behaviour of helium in neutron-irradiated copper-boron alloys was investigated in the temperature range between 300° C and 800° C. It was found that bubbles nucleate preferentially upon dislocations which are created by the annealing of displacement damage. After gas precipitation is complete, the bubbles grow by migration and coalescence, at such a rate that the average bubble radius is proportional to t 1 14, where t is time. Helium causes solution-hardening and the strength of an alloy containing bubbles is inversely proportional to the bubble spacing. One atomic per cent of helium causes a 3 μohm · cm increase in electrical resistivity. The changes which occur in the resistance during annealing are complicated and contributions arise from the concentration of helium in solution and the changing distribution of bubbles. An activation energy of 0.98 ± 0.1 eV was obtained for the first stage of annealing during which all of the gas leaves solution to form bubbles