A new heavy neutron-rich isotope Pa-239 has been produced in the inter
action of 50-MeV/u O-18 ions with U-nat targets, Protactiniun products
were separated radiochemically from the complex mixture of the reacti
on products, The results observed from the decay of Pa-239 and its dau
ghter, U-239, show that the new heavy-rich isotope Pa-239 was synthesi
zed and identified for the first time, The half-life of the Pa-239 was
determined to be 106 +/- 30 min.