Radiative proton capture to the ground state and first three excited states of 12C

The Hoyle state in 12 C

“…There are indications for this effect in the proton capture data, but the main effect is that the cross section for capture to the Hoyle-state is much less than that to the ground state. This has been understood as an effect of the strong α-clustering of the Hoyle-state, which makes coupling to the p+ 11 B channel weak [110]. An alternative explanation [111] could be that the large size of the Hoyle-state leads to a lowering of the dipole strength in analogy to what has been observed for Halo nuclei [112].…”

“…Finally, the Hoyle-state has been populated from higher lying continuum states in the giant resonance region in both 9 Be( 3 He,γ) 12 C and 11 B(p,γ) 12 C [109,110]. These measurements were motivated by mapping out the giant dipole resonance (GDR) built on the Hoyle-state, and comparing that to the GDR built on the ground state of 12 C. In the weak coupling limit it is expected that the GDR built on the Hoyle-state should be shifted up in energy by the excitation energy of the Hoyle-state.…”

Giant Resonances in Excited Nuclei

“…In radiative capture the strength of the GDR as well as its shape may be affected by its coupling to the entrance channel. For example, the (p, y) cross section populating the GDR built on the fi rst excited 0+ state of 12C is very small (24). Since this state has predominantly a 4p-4h configuration relative to the 0+ ground state, a collective p-h resonance built on this state will not couple to an entrance channel consisting of a proton (or neutron) plus target ground state, which is predominantly a Ip-Ih configuration.…”

Low energy spectrum and giant multipole resonances of12C (I)

“…As pointed out above the lowest 0 + state at 7.65 MeV can not be described in our approach, as its dominant structure involves presumably (4p4h) excitations [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]34]. Otherwise, our calculation shows mainly E0-strength in the giant resonance region exhausting about 30/oo of the EWSR limit.…”