Coulomb excitation of radioactive Na21 and its stable mirror Ne21

The low-energy structures of the mirror nuclei Ne-21 and radioactive Na-21 have been examined by using Coulomb excitation at the TRIUMF-ISAC radioactive ion beam facility. Beams of similar to 5x10(6) ions/s were accelerated to 1.7 MeV/A and Coulomb excited in a 0.5 mg/cm(2) Ti-nat target. Scattered beam and target particles were detected by the segmented Si detector BAMBINO, while gamma rays were observed by using two TIGRESS HPGe clover detectors perpendicular to the beam axis. For each isobar, Coulomb excitation from the 3/2(+-) ground state to the first excited 5/2(+-) state was observed and B(E2) values were determined by using the 2(+)-> 0(+) de-excitation in Ti-48 as a reference. The phi segmentation of BAMBINO was used to deduce tentative assignments for the signs of the mixing ratios between the E2 and M1 components of the transitions. The resulting B(E2)up arrow values are 131 +/- 9 e(2) fm(4) (25.4 +/- 1.7 W.u.) for Ne-21 and 205 +/- 14 e(2) fm(4) (39.7 +/- 2.7 W.u.) for Na-21. The fit to the present data and the known lifetimes determined E2/M1 mixing ratios and B(M1)down arrow values of delta=(-)0.0767 +/- 0.0027 and 0.1274 +/- 0.0025 mu(2)(N) and delta=(+)0.0832 +/- 0.0028 and 0.1513 +/- 0.0017 mu(2)(N) for Ne-21 and Na-21, respectively (with Krane and Steffen sign convention). By using the effective charges e(p)=1.5e and e(n)=0.5e, the B(E2) values produced by the p-sd shell model are 30.7 and 36.4 W.u. for Ne-21 and Na-21, respectively. This analysis resolves a significant discrepancy between a previous experimental result for Na-21 and shell-model calculations.