Probing the Statistical Decay andα-clustering effects in12C +12C and14N +10B reactions

L Morelli,S Valdrè,D Fabris,M Bruno,G Casini,S Barlini,S Piantelli,M Cinausero,M D’Agostino,F Gulminelli,M Degerlier,N Gelli,M Bini,T Marchi,A Lopez,F Gramegna,G Pasquali,G Baiocco

doi:10.1051/epjconf/20146603064

Abstract

An experimental campaign has been undertaken at INFN Laboratori Nazionali di Legnaro, Italy, in order to progress in our understanding of the statistical properties of light nuclei at excitation energies above particle emission threshold, by measuring exclusive data from fusion-evaporation reactions. A first reaction 12C+12C at 7.9 AMeV beam energy has been measured, using the GARFIELD+Ring Counter experimental setup. Fusion-evaporation events have been exclusively selected. The comparison to a dedicated Hauser-Feshbach calculation allows us to give constraints on the nuclear level density at high excitation energy for light systems ranging from C up to Mg. Out-of-equilibrium emission has been evidenced and attributed both to entrance channel effects favoured by the cluster nature of reaction partners and, in more dissipative events, to the persistence of cluster correlations well above the 24Mg threshold for 6 alphas decay. The 24Mg compound nucleus has been studied with a new measurement 14N + 10B at 5.7 AMeV. The comparison between the two datasets would allow us to further constrain the level density of light nuclei. Deviations from a statistical behaviour can be analyzed to get information on nuclear clustering.

Highlights

The determination of the nuclear level density in the A∼20 region, the understanding of the statistical behaviour of light nuclei with excitation energies ∼3 A.MeV, and the measurement of observables linked to the presence of cluster structures of nuclear excited levels are the main physics goals of this work
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 [1]; according to the Ikeda diagrams [2] alpha-clustered excited states are massively expected at high excitation energies close to the multi-alpha decay threshold in all even-even N = Z nuclei
The energy spectra of protons and α particles detected at GARFIELD angles are shown in Fig. 1, for the 14N reaction and compared to HF [9] calculations and data from 12C+12C

Summary

Introduction

The determination of the nuclear level density in the A∼20 region, the understanding of the statistical behaviour of light nuclei with excitation energies ∼3 A.MeV, and the measurement of observables linked to the presence of cluster structures of nuclear excited levels are the main physics goals of this work. Signatures of cluster structure in the reactions are expected to be more evident even at high excitation energy.

Results

Conclusion