Nuclear spins, magnetic moments and α-decay spectroscopy of long-lived isomeric states in 185 Pb

Alpha-decay properties of the neutron-deficient isotope 185Pb were studied at the PSB-ISOLDE (CERN) on-line mass separator using the resonance ionisation laser ion source (RILIS). The nuclei of interest were produced in a 1.4 GeV proton-induced spallation reaction of a uranium graphite target. In contrast to previous studies, two α-decaying isomeric states were identified in 185Pb. The relative production of the isomers, monitored by their α-counting rates, could be significantly changed when a narrow-bandwidth laser at the RILIS setup was used to scan through the atomic hyperfine structure. Based on the atomic hyperfine structure measurements, along with the systematics for heavier odd-mass lead isotopes, the spin and the parity of these states were interpreted as 3/2- and 13/2+ and their nuclear magnetic moments were deduced. The α-decay energy and half-life value for the Iπ = 13/2+ isomer are Eα = 6408(5) keV, T1/2 = 4.3(2) s, respectively; while for the Iπ = 3/2- isomer ( T1/2 = 6.3(4) s) two α-decays with Eα1 = 6288(5) keV, Iα1 = 56(2)% and Eα2 = 6486(5) keV, Iα2 = 44(2)% were observed. By observing prompt α-γ coincidences new information on the low-lying states in the daughter isotope 181Hg was obtained.