Extension of the T /sub z/ = -3/2 series of beta-delayed proton precursors in the fp shell. [excitation energy, transition rates, log FT values, B strength, J,. pi.

Abstract

Beta-delayed proton studies of the T /sub z/ = -3/2, A = 4n+1 series were undertaken to obtain high resolution low background spectra of /sup 29/S and to extend the series into the fp shell with the observation of /sup 53/Ni, /sup 57/Zn, and /sup 61/Ge. Development of a pulsed-beam system in which large detection geometries were obtained was crucial in characterizing the latter nuclei due to low production cross sections (50 to 90 nb) for the /sup 40/Ca(heavy ion, 3n) reactions. Spectroscopic studies of the beta-delayed proton decay of /sup 29/S have yielded branching ratios and log ft values for 21 proton unbound levels in /sup 29/P. Comparisons of excitation energies of these levels and ..beta..-decay transition rates feeding them are made to recent shell model predictions. Indications of possible isospin mixing with the lowest T = 3/2 state in /sup 29/P or the presence of a collective Gamow-Teller transition as predicted by the gross theory of ..beta..-decay are indicated by enhanced transition rates to T = 1/2 states located within 300 keV of the isobaric analog state. Comparing the ft values for ..beta../sup +/-decay of /sup 29/S to the mirror ..beta../sup -/-decay of /sup 29/Al resulted in (ft)/sup +//(ft)/sup -/ = 1.04+-0.07, indicating good mirror symmetry. Exploiting the unique signature of delayed proton emission, the decays of several nuclei in the unknown neutron-deficient region of the fp shell were characterized.The following precursors and delayed proton groups were observed. /sup 53/Ni - Ep(c.m.) = 1.94+-.05 MeV, T1/2 = 45+-15 ms; /sup 57/Zn - Ep(c.m.) = 1.95+-.05, 2.58+-.05, and 4.65+-.05 MeV, T1/2 = 40+-10 ms; /sup 61/Ge - Ep(c.m.) = 3.15+-.07 MeV, T1/2 = 40+-15 ms. All of these proton groups (except the 2.58 MeV group of /sup 57/Zn) are attributed to the decay of the lowest T = 3/2 state in the emitter which is populated by a stron superallowed ..beta..-decay branch (approx.50%) from the precursor. 127 references.