Étude expérimentale de transitions électromagnétiques dans le noyau 28Mg

Structure of Mg28 and influence of the neutron pf shell

“…Taking into account the data from Refs. [13,14], the CCEI calculations with effective charges best reproduce the trend of observed B(E2; I i → I i −2) values in 28 Mg. For the SA-NCSM calculations, uncertainties were determined for each data point and are plotted in Figure 9, with lower and upper limits corresponding to calculations in 9 and 11 major harmonic oscillator shells respectively. Taking these uncertainties into consideration, the SA-NCSM calculations are in the best agreement with the experimentally observed B(E2; 4 + 1 → 2 + 1 ) value, and are within the limits of the other data from this study.…”

“…Experimentally determined B(E2) values for the yrast band of28 Mg, from this work and previous studies[13,14], compared to calculated values derived from various interaction models.…”

“…For the 4 + 1 level at 4021. 4(3) keV, the present evaluated lifetime of 1.5(5) × 10 2 fs [19] was based on two conflicting measurements by Fintz et al [13] and Fisher et al [14], as summarized in Table V. This disagreement has implications for the structure of the yrast band, as the measurement of Fintz et al implies increasing B(E2; I i → I i − 2) transition strength with increasing spin -consistent with a rotational or vibrational model, while the measurement of Fisher et al implies the opposite.…”

“…Even for low-lying levels, the existing lifetime measurements often carry large uncertainties. For instance, the two existing measurements of the 4 + 1 → 2 + 1 transition rate in 28 Mg disagree significantly [13,14], leading to opposing conclusions as to the degree of collectivity of states in the yrast band. Furthermore, almost no data exists for states with spin I > 4 and/or high excitation energy where the influence of intruder orbitals is expected.…”