Synthesis and identification of a new heavy neutron-rich isotope Th-238

The unreported heavy neutron-rich nuclide Th-238 has been produced by 60 Me V/nucleon O-18 ion bombardment of natural uranium. Thorium was radiochemica lly separated from the uranium and reaction products. The growth and decay of Pa-238 gamma rays has been observed, identifying the Pa-238 parent as Th -238. The half-life of Th-238 has been determined to be 9.4+/-2.0 min. At t he same time, a new gamma ray of 89.0+/-0.3 KeV was found in the gamma spec trum gated with K alpha(1) x rays of Pa and tentatively assigned to Th-238 decay. [S0556-2813(99)01401-6].