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

Alpha-decay properties of the neutron-deficient isotope Pb-185 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 alpha-decaying isomeric states were identified in Pb-185. The relative production of the isomers, monitored by their alpha-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 alpha-decay energy and half-life value for the I-pi = 13/2(+) isomer are E-alpha = 6408(5) keV, T-1/2 = 4.3(2) s, respectively; while for the I-pi = 3/2(-) isomer (T-1/2 = 6.3(4) s) two alpha-decays with E-alpha1 = 6288(5) keV, I-alpha1 = 56(2%) and E-alpha2 = 6486(5) keV, I-alpha2 = 44(2)% were observed. By observing prompt alpha-gamma coincidences new information oil the low-lying states in the daughter isotope Hg-181 was obtained.