Beta-delayed proton decay in the lanthanide region

Abstract

A total of 24 new ..beta..-delayed proton precursors and several new decay branches in the region of 56 < Z < 72 and N < 82 have been identified with the OASIS on-line mass separator facility at the SuperHILAC in Berkeley. Proton spectra and halflives were measured for all precursors. Additional properties determined for many of the isotopes include spins and parities of the precursors, final state feedings, proton branching ratios, (Q/sub EC/-S/sub p/) energy differences, and new levels in the proton decay daughters. Mixed ..beta..-delayed proton decay from precursor isomers and ground states has been observed. The proton decay has been compared to statistical model calculations using Gamow-Teller (GT) ..beta..-strength functions obtained from RPA calculations with Nilsson model wave functions. For the N = 81 precursors /sup 151/Yb, /sup 149/Er, and /sup 147/Dy, pronounced structure in the proton spectra has been observed. An interpretation of this structure in the framework of ''doorway'' states is proposed. 25 refs., 6 figs., 1 tab.