Decay studies of the long-lived states in Tl186

Abstract

Decay spectroscopy of the long-lived states in 186 Tl has been performed at the ISOLDE Decay Station at ISOLDE, CERN. The α decay from the low-spin (2 −) state in 186 Tl was observed for the first time and a half-life of 3.4 +0.5 −0.4 s was determined. Based on the α-decay energy, the relative positions of the long-lived states were fixed, with the (2 −) state as the ground state, the 7 (+) state at 77(56) keV, and the 10 (−) state at 451(56) keV. The level scheme of the internal decay of the 186 Tl(10 (−)) state [T 1/2 = 3.40(9) s], which was known to decay solely through emission of 374-keV γ-ray transition, was extended and a lower limit for the β-decay branching b β > 5.9(3)% was determined. The extracted retardation factors for the γ decay of the 10 (−) state were compared to the available data in neighboring odd-odd thallium isotopes indicating the importance of the π d 3/2 shell in the isomeric decay and significant structure differences between 184 Tl and 186 Tl.