Studies of interaction between He and elements with mass number 140 in Fe by time-differential perturbed-angular-correlation measurements

Room-temperature time-differential perturbed-angular-correlation (TDPAC) spectra of Ce-140 arising through Ba-140-La-140 from Cs-140 in He-doped Fe, unannealed and annealed in vacuum at various temperatures, were obtained in order to examine whether Ce (or rather, La and Ba) and He form complexes having a definite geometrical structure in Fe, as suggested by first-principles density-functional theory calculations. No clear signal of such complexes was observed in the TDPAC spectra. However, the TDPAC spectra indicate that Ce and He form complexes having a variety of geometrical structures. Comparison with reported TDPAC results on Cd-111 arising from In-111 in He-doped stainless steel shows that the parent atoms (La and Ba) of Ce-140 trap He atoms more efficiently than In atoms do, indicating stronger bonding of He to the former atoms, while different from the present case, Cd-111 (In)-He complexes form a unique geometrical structure.