Coulomb excitation of radioactive 20, 21 Na

The low-energy structures of the radioactive nuclei 20, 21 Na have been examined using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. Beams of ∼ 5×10 6 ions/s were accelerated to 1.7MeV/A and Coulomb excited in a 0.5mg/cm^2 nat Ti target. Two TIGRESS HPGe clover detectors perpendicular to the beam axis were used for γ -ray detection, while scattered nuclei were observed by the Si detector BAMBINO. For 21 Na , Coulomb excitation from the 3/2 + ground state to the first excited 5/2 + state was observed, while for 20 Na , Coulomb excitation was observed from the 2 + ground state to the first excited 3 + and 4 + states. For both beams, B ( λ L ) values were determined using the 2 + → 0 + de-excitation in 48 Ti as a reference. The resulting B ( E 2) ↓ value for 21 Na is 137±9 e^2fm^4, while the resulting B ( λ L ) ↓ values for 20 Na are 55±6 e^2fm^4 for the 3 + → 2 + , 35.7±5.7 e^2 fm^4 for the 4 + → 2 + , and 0.154±0.030 μ_ N ^2 for the 4 + → 3 + transitions. This analysis significantly improves the measurement of the 21 Na B ( E 2) value, and provides the first experimental determination of B ( λ L ) values for the proton dripline nucleus 20 Na .-1