Collins Russian Dictionary 2nd Edition © HarperCollins Publishers 2000, 1997:
concentration [kɔnsənˈtreɪʃən] n сосредото́чение, концентра́ция (attention) сосредото́ченность f (CHEM) концентра́ция
* is used to mark translations which have irregular inflections. The Russian-English side of the dictionary gives inflectional information.