Helium-helium clustering states in Be 12

An inelastic excitation experiment was performed with a Be12 beam at 29 MeV/u on a carbon target. New resonances close to the respective cluster separation thresholds were observed in Be12 for the He4+He8 and He6 + He6 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 He4 + He8 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 Be12 is well demonstrated. The detection focused on the most forward angles, by using a zero-deg telescope, is essential in the present measurement.