Change in structure between the I=1/2 states in 181Tl and 177,179Au

The first accurate measurements of the alpha-decay branching ratio and half-life of the Ipi = 1/2+ ground state in 181Tl have been made, along with the first determination of the magnetic moments and I=1/2 spin assignments of the ground states in 177,179Au. The results are discussed within the complementary systematics of the reduced alpha-decay widths and nuclear g factors of low-lying, Ipi = 1/2+ states in the neutron-deficient lead region. The finding shed light on the unexpected hindrance of the 1/2+->1/2+, 181Tl(g) -> 177Au(g) alpha decay, which is explained by a mixing of pi3s1/2 and pi2d3/2 configurations in 177Au(g), whilst 181Tl(g) remains a near-pure pi3s1/2. This conclusion is inferred from the g factor of 177Au(g) which has an intermediate value between those of pi3s1/2 and pi2d3/2 states. A similar mixed configuration is proposed for the Ipi=1/2+ ground state of 179Au. This mixing may provide evidence for triaxial shapes in the ground states in the these nuclei.