Étude expérimentale de transitions électromagnétiques dans le noyau ²⁸Mg

Abstract

The first five excited states of ²⁸Mg have been studied by observing γ-rays from the ²⁶Mg(t,pγ)²⁸Mg reaction, in coincidence with protons, in NaI(Tl) and Ge(Li) detectors, at incident energies between 2.5 and 3.2 MeV. Doppler-shift attenuation measurements lead to the mean-lives τ_m = 2.0±0.4 ps, 1.1±0.3 ps and 96±30 fs for the levels at 1.47, 3.86 and 4.02 MeV, respectively, and to upper limits of τ_m < 50 fs and < 120 fs for the levels at 4.56 and 4.88 MeV. Angular correlation measurements (method II) were used to determine spins, mixing ratios and γ-branching ratios. The 4.02 MeV level has most probably J^γ = 4⁺.