  We have successfully synthesized one member of LnFeAsO (Ln stands for
lanthanides) with Ln=Tb. By partial substitution of Tb$^{3+}$ by Th$^{4+}$,
superconductivity with onset $T_{c}$ up to 52 K was observed. In the undoped
parent compound, the magnetic moments of Tb$^{3+}$ ions order
antiferromagnetically (AFM) at $T_N$ of 2.5 K, and there exists an anomaly in
the resistivity at $T^*$ of about 124 K which corresponds to the structural
phase transition and/or AFM ordering of magnetic moments of Fe$^{2+}$ ions.
This anomaly is severely suppressed by Th doping, similar to the cases of F
doped LnFeAsO series. Thermopower measurements show that the charge carrier is
electron-like for both undoped and Th doped compounds, and enhanced thermopower
in Th doped samples was observed.
