Narrow Results

It is discussed that the recently observed 0⁺ state at 13.5 MeV in ¹⁶O can be a good candidate of the 4α condensate. The 4α condensed state which is theoretically obtained in the vicinity of the 4α threshold is shown to have a relatively large α decay width, which is in well agreement with the value measured for the 0⁺ state at 13.5 MeV. The analysis of inelastic form factor of electron scattering to the 4α condensed state is made by artificially varying the size of the 4α condensate. Similarly to the case of Hoyle state, only the magnitude of the form factor is found to depend on its size, while the position of maximum and minimum are not changed.

We attempt at describing the particle-hole and cluster excitations for A ~ 16 nuclei in a single scheme of a ¹²C core plus few-nucleon model. A nucleon-¹²C potential is derived based on a collective model taking into account the core excitation and its parameters are determined to reproduce the low-lying spectrum of ¹³C. The model is tested in three- and four-body systems, ¹⁴C, ¹⁴N and ¹⁵C. Preliminary results of the five-body systems for ¹⁶C and ¹⁶O are reported.

In order to search for the α condensed state in ¹⁶O, we have performed the decay particle measurement via the reaction. Although the decay branching ratio of the α + ¹²C channel was predicted to be small, the branching ratio between the α + ¹²C and channels was obtained to be 7:3 by using the result of a simple simulation.