Abstract: | It is well known that the observation of a nonzero Fermi matrix element for a β-transition between states that differ in isospin can provide information about the relative isospin purity of the states involved. We have determined the log ft value for the 0+ → 0+ (ΔT ≠ 0) β-transition in decay as 6.516 ± 0.020. From this log ft value, we have deduced |MF| = (43.4 ± 1.1) × 10?3, |α| = (21.7 ± 0.6) × 10?3 and |〈VCD〉| = 41.7 ± 1.1 keV, where MF,α2 and 〈VCD〉 represent the Fermi matrix element, isospin impurity and Coulomb matrix element, respectively. The Coulomb matrix element of 41.7 keV found for 64Ga is one of the largest known from β-decay experiments. The experimental procedure involved a careful measurement of the intensity of the annihilation radiation relative to that of the other γ-rays from 64Ga decay. As a by-product, we have obtained an improved 64Ga decay scheme. We have also summarized the existing information on the isospin impurities of nuclear states as deduced from β-decay experiments. |