Search for oscillation of the electron-capture decay probability of Pm

We have searched for time modulation of the electron capture decay probability of ¹⁴²Pm in an attempt to confirm a recent claim from a group at the Gesellschaft für Schwerionenforschung (GSI). We produced ¹⁴²Pm via the ¹²⁴Sn(²³Na, 5n)¹⁴²Pm reaction at the Berkeley 88-Inch Cyclotron with a bombardment time short compared to the reported modulation period. Isotope selection by the Berkeley Gas-filled Separator is followed by implantation and a long period of monitoring the ¹⁴²Nd Kα${\text{K}}_{\alpha }$ x-rays from the daughter. The decay time spectrum of the x-rays is well-described by a simple exponential and the measured half-life of 40.68(53) seconds is consistent with the accepted value. We observed no oscillatory modulation at the proposed frequency at a level 31 times smaller than that reported by Litvinov et al. [Y.A. Litvinov, et al., Phys. Lett. B 664 (2008) 162]. A literature search for previous experiments that might have been sensitive to the reported modulation uncovered another example in ¹⁴²Eu electron-capture decay. A reanalysis of the published data shows no oscillatory behavior.