Decay spectroscopy of the very neutron-deficient lead and thallium isotopes 178,179Pb and ¹⁷⁹Tl

Abstract

This thesis reports on the production of the very neutron-deficient isotopes 178,179Pb and 179Tl, using heavy-ion fusion-evaporation reactions. The gas-filled separator RITU and the GREAT spectrometer at its focal plane position were used for the decay spectroscopy study. The α decay of 178Pb and its α-decay chain were studied through α-α correlations. The α-particle energy and half-life were measured for 178Pb as, Eα= 7610(30) keV and t1/2 = 0.21−+0.21

0.08 ms, respectively. The half-life is consistent with recent theoretical calculations using the Coulomb and Proximity Potential Model (CPPM). The hindrance factor for 178Pb was deduced and corresponds to an unhindered Δl = 0 transition. The α-decay reduced width was deduced as well and put into a systematic context advancing the systematics of the even-A Pb isotopes to further neutron deficiency. The decay properties of 179Pb were studied through α-α and α-γ correlations, which has allowed the ground-state of 179Pb to be assigned as Iπ = 9/2−. In comparison with the literature, a more precise α-particle energy and half-life were measured for the ground state of 179Pb to be, Eα = 7348(5) keV and t1/2 = 2.7(2) ms, respectively. A search for a νi13/2 state in 179Pb was performed, but only a limit of excitation energy and half-life was obtained. In addition, improved α-decay data were also measured for 179Tl. Evidence for an isomeric state at an excitation energy of 904.5(9) keV was identified for the first time in 179Tl, with a half-life of t1/2 = 114−+18

10 ns and is tentatively

assigned to be a proton (9/2−) intruder state.