Purpose: Transition matrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus Na-26 with 7 valence neutrons and 3 valence protons outside the doubly-magic O-16 core is used as a test case.
Method: A radioactive beam experiment with Na-26 (T-1/2 = 1,07s) was performed at the REX-ISOLDE facility (CERN) using Coulomb excitation at safe energies below the Coulomb barrier. Scattered particles were detected with an annular Si detector in coincidence with gamma rays observed by the segmented MINIBALL array. Coulomb excitation cross sections of the beam have been obtained by normalization to the well known Coulomb excitation cross sections of the Pd-104 target.
Results: The observation of three gamma-ray transitions in Na-26 together with available spectroscopic data allows us to determine E2- and M1-transitional matrix elements. Results are compared to theoretical predictions.
Conclusion: The improved theoretical description of Na-26 could be validated. Remaining discrepancies between experimental data and theoretical predictions indicate the need for future experiments and possibly further theoretical improvements.