ALPHA-DECAY OF A NEW ISOTOPE TH-209

The new neutron deficient isotope Th-209 has been produced in the reac tion of S-32 on W-182 at beam energy of 171 MeV. Evaporation residues were separated in flight from beam by a JAERI recoil mass separator, a nd implanted in a position sensitive strip detector. The genetic corre lation of alpha-decay events, their energies and half-lives has been u sed to identify isotopes. An alpha-decay energy and a half-life of Th- 209 have been determined to be 8.080(50) MeV and 3.8(-1.5)(+6.9) ms, r espectively.