Nuclear reaction analysis and ion implantation techniques were used to investigate the trapping of deuterium (D) by He bubbles and implantation defects in Ta. A series of four complementary temperature ramp experiments have enabled us to determine that: (1) the binding enthalpy of D at trap sites associated with He bubbles in Ta is 0.53plusmn;0.05 eV relative to solution sites; (2) the binding enthalpies of D at implantation defects in Ta are 0.53plusmn;0.10, 0.42plusmn;0.10, and 0.33plusmn;0.10 eV; and (3) the approximate number of He bubble trap sites produced per He atom implanted into Ta is 0.45 for mean He atomic fractions ranging from 1.5percnt; to 2.5percnt;. The measured binding enthalpies are compared with effectivehyphen;medium theory calculations of the binding enthalpies of both hydrogen chemisorption sites and monovacancy sites containing from one to six trapped hydrogen atoms. This comparison suggests that the strongest 0.53hyphen;eV traps associated with implanted He are bubbles which trap hydrogen on their interior surface via a chemisorptionlike mechanism. The strong 0.53hyphen;eV defect trap sites are probably vacancy clusters, whereas the 0.42hyphen;eV defect traps appear to be monovacancy sites containing one to two hydrogen atoms, and the 0.33hyphen;eV sites appear to be monovacancy sites containing three to six hydrogen atoms.
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