The influence of surface oxygen on release of deuterium from tantalum

Here we examine the influence of surface oxygen on both the absorption of deuterium (D) from gas into solution i tantalum (Ta) and the release from solution back to the gas. The D uptake rate was proportional to gas pressure with a sticking coefficient of 0.0085 {plus minus} .00025 for clean Ta surfaces. Exposure to 10 Langmuirs (L) of O{sub 2}, giving about one monolayer of chemisorbed oxygen, decreased the D uptake rate by about two orders of magnitude. D release was studied using the D({sup 3}He,P){alpha} nuclear reaction to measure the concentration of D in the Ta versus time during release at constant temperature. D release was surface-limited and obeyed second order kinetics for both clean and oxygen covered Ta surfaces which shows that molecular recombination must be occurring from sites which have much smaller binding energies for D than the low-coverage chemisorption sites. Exposure to 10{sup 6} L of O{sub 2} resulted in an additional energy barrier to D recombination of 0.25 {plus minus} .04 eV/D which greatly reduces the D release rate. This activation barrier should also reduce D dissociation and uptake rates as observed. 17 refs., 7 figs.