ELECTRON-CAPTURE DECAY OF U-231

We studied the electron-capture decay of U-231, produced by bombarding U-233 targets with 49-MeV protons in the 88-Inch. Cyclotron at the La wrence Berkeley Laboratory. Following chemical separation, we measured the U-231 (T-1/2 = 4.2 d) activity with semiconductor detectors. The gamma-ray, X-ray and conversion-electron data from singles and coincid ence measurements confirmed the known level scheme of Pa-231. Almost a ll of the vacancies in the atomic K shell are produced by electron cap ture in the decay of U-231. Thus, the relative K X-ray intensities can be used in a straightforward manner to normalize the decay scheme and deduce photon emission probabilities. The gamma-ray data agree with p revious values determined with NaI detectors, but were measured much m ore precisely in this work.