An inelastic excitation experiment was performed with a 12 Be beam at 29 MeV/u on a carbon target. New resonances close to the respective cluster separation thresholds were observed in 12 Be for the 4 He + 8 He and 6 He + 6 He decay channels, confirming the previously proposed molecular rotational bands. Using the model-independent angular correlation analysis, a 0 + spin parity is assigned to the remarkably large peak at 10.3 MeV in the 4 He + 8 He channel. A distorted wave Born approximation (DWBA) calculation was compared to the experimental differential cross section of this state, resulting in a largely enhanced monopole transition matrix element of 7.0 ± 1.0 fm 2 , in good agreement with the generalized two-center cluster model (GTCM) prediction assuming a preformed α-4n-α configuration. Together with the previously reported large cluster spectroscopic factor, the strong clustering in 12 Be is well demonstrated. The detection focused on the most forward angles, by using a zero-deg telescope, is essential in the present measurement.

A new one-neutron adding reaction on 11 Be was performed at 26.9A MeV. The elastic scattering data was measured simultaneously to determine the target component and optical potentials for the entrance channel. A special isomer-tagging method was used to determine the cross sections for the 0 + 2 state. Based on the ratio of the s−wave spectroscopic factors of the 0 + 1 and 0 + 2 states, along with the previously reported p−wave intensities, the s− and d−wave components of these two states were obtained and compared with shell model calculations using various interactions. The result shows a dominant d−wave strength in the ground state of 12 Be, and reveals the dominance of sd-and sp-single-particle configurations in the 2 + and 1 − state of 12 Be, respectively. Together with the configuration mixing analysis, the relative spectroscopic factors, which are shown to be less sensitive to the different choice of optical potentials, provide important insights on the wave functions for the low-lying states of 12 Be.