DOUBLE K-SHELL VACANCY PRODUCTION IN THE ELECTRON-CAPTURE DECAY OF CE-139

The probability of double K-shell vacancy production in the electron capture decay of Ce-139 to the 166-keV level of La-139 has been investigated. Triple coincidences between the 166-keV gamma ray, the La satellite K alpha x ray, and the La hypersatellite K alpha x ray were measured using two intrinsic Ge detectors. We looked for the sum of two of the three radiations in one detector in coincidence with the third radiation in the other detector. The probability of double K-shell vacancy production per K-shell electron capture (P(KK)) was found to be (2.0 +/- 1.6) x 10(-6). From this and the known P(KK) for Cs-131 we estimate a probability for zero K-shell vacancy production (shakedown) per K-shell electron capture of less-than-or-approximately 2.4 x 10(-5) for Ce-139.