Abstract
In the recent years, cluster structures have been evidenced in many ground and excited states of light nuclei [1, 2]. The decay of highly excited states of 24 Mg is studied in fusion evaporation events completely detected in charge in the reactions 12 C+ 12 C and 14 N+ 10 B at 95 and 80 MeV incident energy, respectively, and compared to the results of a pure statistical model [3, 4]. Inclusive variables are in general well reproduced by the model. We found clear deviations from the statistical model if we select emission channels involving multiple α particles which are more probable than expected from a purely statistical behavior. Data from 12 C+ 12 C reaction have been analyzed in order to study the decay of the Hoyle state of 12 C* with two different selections: peripheral binary collisions and 6α decay channel in central events. To continue the investigation on light systems, we have recently measured the 16 O+ 12 C reaction at three different beam energies, namely E beam = 90, 110 and 130 MeV. Preliminary results are presented.
Highlights
The NUCL-EX collaboration has recently started an experimental campaign of exclusive measurements of fusion-evaporation reactions with light nuclei as interacting partners
Energy spectra for protons and α particles detected at GARFIELD angles are plotted in figure 1, for residues of different charge, for the 14N reaction, and compared to HF [4] calculations and to data for the 12C+12C reaction
Some discrepancies are present in events with an Oxygen residue, where the energy tails for α particles are not reproduced by the model, especially for the 12C+12C case
Summary
The NUCL-EX collaboration has recently started an experimental campaign of exclusive measurements of fusion-evaporation reactions with light nuclei as interacting partners. Despite the interest of this issue, few studies, mainly based on inclusive experiments, exist on the evaporation of very light nuclei (A ∼ 20 region) at relatively high excitation energy (ε∗ ≈ 3 A.MeV). Some excited states of different nuclei in this mass region are known to present pronounced cluster structures These correlations may persist in the ground state along some selected isotopic chains [6] and, according to the Ikeda diagrams [2], α-clustered excited states are sizeably expected at high excitation energies close to the multi-alpha decay threshold in all even-even N = Z nuclei. Concerning experimental research, rotational bands consistent with α-cluster structures have been identified in different even-even light nuclei and shown to persist even along their isotopic chains Such effects can be experimentally seen as an excess of cluster production with respect to the prediction of the statistical model, provided that the ingredients of the latter are sufficiently constrained via experimental data. It is interesting for such systems that they can be studied at different beam energies, extracting information on how (and to what extent) structure effects are still at play in the decay of hot nuclei at different excitation regimes
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