Exotic Molecular States in12Be

Abstract

The breakup of 12 Be into 6 He 1 6 He and 4 He 1 8 He has been studied using a 378 MeV 12 Be beam inelastically excited by 12 C and ͑CH 2 ͒ n targets. The measurements indicate that breakup occurs from rotational states in the 10 to 25 MeV excitation energy interval, with spins in the range of 4h to 8h. The inferred moment of inertia is consistent with the cluster decay of an exotic molecular structure in 12 Be, which may be associated with an a-4n-a cluster configuration. [S0031-9007(99)08451-3]

A new experimental study of the12Be cluster structure

“…The 13.3MeV state corresponds to the 13.2MeV state reported by Freer et al [15], while the 11.7MeV peak was not seen in the two previous experiments due to the limited acceptance of their detector systems at low excitation energy side (Fig 1(b)). In case of the 4 He+ 8 He coincident events, two peaks at 10.2MeV, and 13.4MeV can be identified.…”

“…The resolution(FWHM) is determined to be around 0.4MeV at a relative energy(E rel ) of 1MeV and increases to about 0.8MeV at E rel of 4MeV as shown in Fig 1(a). The small size of the CsI scintillators and the angular coverage of the telescope from 0 o offered higher sensitivity in case of small relative energies compared to detector systems of Freer et al [15] and Charity et al [16]. The detection efficiency for 12 Be decaying into 2-X He fragments is thus determined to be around 40% in average, as shown in Fig 1(b) for 12 Be decaying into 4 He+ 8 He.…”

“…The reconstructed 12 Be excitation energy spectra(not corrected for the detection efficiency) for 6 He+ 6 He and 4 He+ 8 He are displayed in Fig 3(a) and (b), respectively. [15,16,22] and the results of this work, while the GTCM calculation is from [21].…”

“…So far, there have been some inconsistence in the rather limited experimental results. Some MR cluster states were reported in the work of Freer et al, from which a 6 He+ 6 He rotational band was constructed in accordance with an α-4n-α cluster configuration [15]. However, most of these resonances were not observed in a later experiment by Charity et al with significantly better statistics [16].…”

“…One possible method to probe the Molecular-Resonance(MR) states is to apply the inelastic excitation followed by coincidently recording the decay products [15,16,19]. So far, there have been some inconsistence in the rather limited experimental results.…”