A method for extracting silicon isotopes was developed. Polycrystalline Si-
28, Si-29, and Si-30 samples isotopically enriched to 99.95, 99.5, and 99.9
%, respectively, were prepared. Energies of optical phonons in the isotopic
ally pure samples show the expected dependence on the average atomic mass.
(C) 2001 MAIK "Nauka/Interperiodica".