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

Abstract The first accurate measurements of the α -decay branching ratio and half-life of the I π = 1 / 2 + ground state in 181 Tl have been made, along with the first determination of the magnetic moments and I = 1 / 2 spin assignments of the ground states in 177,179 Au. The results are discussed within the complementary systematics of the reduced α -decay widths and nuclear g factors of low-lying, I π = 1 / 2 + states in the neutron-deficient lead region. The findings shed light on the unexpected hindrance of the 1 / 2 + → 1 / 2 + , 181 Tl → g 177 Au g α decay, which is explained by a mixing of π 3 s 1 / 2 and π 2 d 3 / 2 configurations in 177 Au g , whilst 181 Tl g remains a near-pure π 3 s 1 / 2 . This conclusion is inferred from the g factor of 177 Au g which has an intermediate value between those of π 3 s 1 / 2 and π 2 d 3 / 2 states. A similar mixed configuration is proposed for the I π = 1 / 2 + ground state of 179 Au. This mixing may provide evidence for triaxial shapes in the ground states in these nuclei.