Activation energies for some processes concerned with hydrogen recombinatio
n were studied experimentally. One side of a nickel membrane was exposed to
a deuterium plasma and the deuterium permeation flux J at a steady state w
as monitored. At the same time, the surface density S of deuterium on the p
lasma-exposed side was observed by nuclear reaction analysis. The results s
howed that both the data of S-2 and J/S fell on straight lines in Arrhenius
diagrams. Considering the particle balance equations under the experimenta
l conditions, two values of the activation energy for the rate constant wer
e obtained: one for two atoms recombining and subsequently leaving from the
surface of 0.40 eV and the other for one atom migrating from the surface t
o the bulk of 0.57 eV. From these values, the energy term in the convention
al form of the recombination coefficient was found to be 0.08 eV. (C) 1999
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