CALCULATION OF HELIUM DISSOCIATION ENERGIES FOR VANADIUM, NIOBIUM AND MOLYBDENUM BY A COMPUTER SIMULATION METHOD.

Atomistic calculations of activation energies of helium dissociation from helium-vacancy clusters in vanadium, niobium and molybdenum have been performed by a computer simulation method. In the process, formation energies of vacancy clusters, interstitial helium and helium-vacancy clusters have been also calculated as well as migration energies of vacancy and helium. Potentials of metal-metal and helium-metal for vanadium and molybdenum were after R. H. Johnson and W. D. Wilson, whereas other potentials were constructed in a similar manner. Calculated dissociation energies in vanadium and niobium are around 3. 0 ev and smaller than those in molybdenum (4. 0 ev to 5. 0 ev). Large helium dissociation energies from small clusters suggest stable agglomeration states of helium in these bcc metals.