Proton inelastic scattering off a neutron halo nucleus, 11 Li, has been studied in inverse kinematics at the IRIS facility at TRIUMF. The aim was to establish a soft dipole resonance and to obtain its dipole strength. Using a high quality 66 MeV 11 Li beam, a strongly populated excited state in 11 Li was observed at E x =0.80 ± 0.02 MeV with a width of Γ = 1.15 ± 0.06 MeV. A DWBA (distorted-wave Born approximation) analysis of the measured differential cross section with isoscalar macroscopic form factors leads to conclude that this observed state is excited in an electric dipole (E1) transition. Under the assumption of isoscalar E1 transition, the strength is evaluated to be ex- * Corresponding author.
Many-body nuclear theory utilizing microscopic or chiral potentials has developed to the point that collectivity might be dealt with in an ab initio framework without the use of effective charges; for example with the proper evolution of operators, or alternatively, through the use of an appropriate and manageable subset of particle-hole excitations.We present a precise determination of E2 strength in 22 Mg and its mirror 22 Ne by Coulomb excitation, allowing for rigorous comparisons with theory. No-core symplectic shell-model calculations were performed and agree with the new B(E2) values while in-medium similarity-renormalization-group calculations consistently underpredict the absolute strength, with the missing strength found to have both isoscalar and isovector components.
The β-decay half-lives of [128][129][130] Cd have been measured with the newly commissioned GRIFFIN γ-ray spectrometer at the TRIUMF-ISAC facility. The time structures of the most intense γ-rays emitted following the β-decay were used to determine the half-lives of 128 Cd and 130 Cd to be T 1/2 = 246.2(21) ms and T 1/2 = 126(4) ms, respectively. The half-lives of the 3/2 + and 11/2 − states of 129 Cd were measured to be T 1/2 (3/2 + ) = 157(8) ms and T 1/2 (11/2 − ) = 147(3) ms. The half-lives of the Cd isotopes around the N = 82 shell closure are an important ingredient in astrophysical simulations to derive the magnitude of the second r-process abundance peak in the A ∼ 130 region. Our new results are compared with recent literature values and theoretical calculations.
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.
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.
Gamma rays from excited states feeding a proton-emitting isomeric-state in 151 Lu have been observed for the first time. Comparison with state-of-the-art nonadiabatic quasiparticle calculations indicates an oblately deformed, 3/2 + proton-emitting state with a quadrupole deformation of β 2 = −0.11. The calculations suggest an increase in quadrupole deformation, to β 2 = −0.18, with increasing spin which is understood in terms of the mixing of Nilsson states at the Fermi surface. It is also shown that the proton decay half-life is consistent with that from a 3/2 + state with a quadrupole deformation of β 2 = −0.12.
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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