Delayed proton emission of N=81 odd-odd precursors: Ho148, Tm150, and Lu152

Beta-delayed proton decay was observed in Ho148, Tm150, and Lu152 for the first time. Contrary to neighboring even-Z N=81 isotones, the proton spectra appear structureless and statistical in nature. Proton branching ratios for the high-spin isomers in these isotopes, based on the intensity of -ray transitions in the intermediate nuclei, are (8-2+1)×10-4, (1.2-0.4+0.2)×10-2, and (1.50.7)×10-1, respectively. The onset of proton emission in all three cases occurs at a proton to width ratio of about 10-4. Protons were found to be in coincidence with x rays, rays, and positrons. Coincident K x rays served to identify the Z of the precursor, while the rays gave quantitative information about proton decay to excited states in the daughter nuclei. By comparing the final state branching ratios with statistical model calculations, it was concluded that Ho148 and Tm150 both have isomers with probable spin values of 1+ and 6-. Statistical model calculations with standard prescriptions for level densities and widths, and with a reduced level density parameter are compared to experiment. To reproduce the shape of the proton spectrum it was necessary to assume Gaussian-shaped Gamow-Teller strength functions centered near 8 MeV excitation energy. In the course of these experiments -delayed proton emission in Er148 was also identified.