To elucidate the nature of the heavy-fermion superconductor U1- xThxBe13, measurements are made of the superconducting and magnetic phase boundaries, and of the dc magnetization as a function of magnetic field and temperature. Heavy-fermion systems are of particular interest as they differ from normal metals in having relatively enormous values of low-temperature specific heat and magnetic susceptibility. The appearance of superconductivity in such media is further surprising and intriguing.
