The unreported heavy neutron-rich nuclide ${}^{238}\mathrm{Th}$ has been produced by $60\hspace{0.5em}\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}{}^{18}\mathrm{O}$ ion bombardment of natural uranium. Thorium was radiochemically separated from the uranium and reaction products. The growth and decay of ${}^{238}\mathrm{Pa}\gamma$ rays has been observed, identifying the ${}^{238}\mathrm{Pa}$ parent as ${}^{238}\mathrm{Th}.$ The half-life of ${}^{238}\mathrm{Th}$ has been determined to be $9.4\pm 2.0\hspace{0.5em}\min .$ At the same time, a new $\gamma$ ray of $89.0\pm 0.3\hspace{0.5em}\mathrm{KeV}$ was found in the $\gamma$ spectrum gated with $K{\alpha }_1$ x rays of Pa and tentatively assigned to ${}^{238}\mathrm{Th}$ decay.

• Received 12 August 1998

DOI:https://doi.org/10.1103/PhysRevC.59.520