H-T phase diagrams of the double transition in thoriated UBe_(13)

We present magnetic field-temperature (H-T) phase diagrams of the double transitions of superconducting U_(1-x)Th_xBe_(13) with x=0.030 and x=0.022. For both samples increasing the applied magnetic field moves the two transitions to lower temperature while decreasing their separation in temperature. For the x=0.030 sample, the transitions remain distinct for T>100 mK. For x=0.022, however, the two transitions appear to merge near H=20 kOe acid T=350 mK, analogous to the situation in the related heavy fermion superconductor UPt_3.