Helium-helium clustering states in 12Be.

An inelastic excitation experiment was performed with a 12Be beam at 29 MeV/u on a carbon target. New resonances close to the respective cluster separation thresholds were observed in 12Be for the 4He + 8He and 6He + 6He 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 4He + 8He 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 ± 1.0fm², 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 12Be is well demonstrated. The detection focused on the most forward angles, by using a zero-deg telescope, is essential in the present measurement. [ABSTRACT FROM AUTHOR]