Lifetimes of prolate intruder states in 186Pb and oblate intruder states in 194Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in 188Pb up to the 8+ state were carried out using the recoil-gating method. The B(E2) values have been deduced from which deformation parameters |beta2|=0.29(5) and |beta2|=0.17(3) for the prolate and the oblate bands, respectively, have been extracted. The results also shed new light on the mixing between different shapes.
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.
The nucleus 203 Fr has been studied through γ -ray and electron spectroscopy, using the recoil-decay tagging technique. A 13/2 + state, with a half-life of 0.37 (5)
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