Lifetimes of yrast states in 180 Hg up to the 8 + state and of the 9 − state have been extracted from recoil-decay tagged γ -ray spectra by using the recoil distance Doppler-shift method. In addition, lifetimes of yrast states up to the 10 + state in 182 Hg have been extracted from recoil-gated γ γ -coincidence spectra. The present study addresses the evolution of collectivity of two competing shapes in neutron-deficient Hg nuclei as a function of A and the configuration mixing at low spin.

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Using fusion-evaporation reactions, a gas-filled recoil separator, and recoil-electron and recoil-electron-α tagging techniques, a new isomeric 1 2 201 At is identified, and an earlier reported corresponding state [T 1/2 = 273( 9) ms] in 199 At is confirmed. The 1 2 + state is suggested to originate from an intruder π (s 1/2 ) −1 configuration. In addition, nuclear structure of states below and above this 1 2 + state are studied in both nuclei. The isomer decays through a cascade of an E3 transition followed by a mixed M1/E2 transition to the 9 2 − ground state, and it is interpreted to be fed from nearly spherical 3 2 + and 5 2 + states originating from π (d 3/2 ) −1 and π (d 5/2 ) −1 configurations, respectively.

The neutron-deficient nucleus 199 At has been studied through γ -ray and electron spectroscopy, using the recoil-decay tagging technique. Two experiments were conducted, using a gas-filled recoil separator with a focal-plane spectrometer alone and together with a germanium-detector array at the target position. The resulting level scheme for 199 At includes a new isomer with a half-life of 0.80(5) µs and a spin and parity of (29/2 + ). The 13/2 + isomer, which de-excites via an M2 transition to the 9/2 − ground state, was measured to have a half-life of 70(20) ns. Our earlier version of the level scheme for 197 At has been updated as well.