Thermal properties of light nuclei from¹²C +¹²C fusion–evaporation reactions

Abstract

Abstract. The12 C+ 12 C reaction at 95 MeV has been studied through the complete charge identification of its products by means of the GARFIELD+RCo experimental set-up at INFN Laboratori Nazionali di Legnaro (LNL). In this paper, the first of a series of two, a comparison to a dedicated Hauser-Feshbach calculation allows to select a set of dissipative events which corresponds, to a large extent, to the statistical evaporation of highly excited 24 Mg. Information on the isotopic distribution of the evaporation residues in coincidence with their complete evaporation chain is also extracted. The set of data puts strong constraints on the behaviour of the level density of light nuclei above the threshold for particle emission. In particular, a fast increase of the level density parameter with excitation energy is supported by the data. Residual deviations from a statistical behaviour are seen in two specific channels, and tentatively associated with a contamination from direct reactions and/or α-clustering effects. These channels are studied in further details in the second paper of the series.PACS numbers: 25.70.z, 24.60.Dr, 27.30.+t, 24.10.Pa NUCLEAR REACTIONS 12C(12C,X), E = 95 AMeV, Measured Fusion-evaporation reactions, Observed deviation from statistical behaviour.

From Light to Heavy Nuclear Systems, Production and Decay of Fragments Studied with Powerful Arrays

“…Clearly, for even-Z channels, there is an eect which is not contained in the model. The eect is evident for the 12 C + 12 C case, where error bars correspond to variations due to dierent cuts on the event Q-value (more or less damped events) [17]. Also in the case of 14 N + 10 B we measure similar deviations with respect to the predicted branching ratios; the eect results even larger for the Ne channel for which the emission of the solely allowed α particle is denitely more favoured in the measurement.…”

“…Detailed results on the symmetric 12 C collision have been extensively published [16,17] while the data analysis of the 14 N + 10 B system is still in progress. Here we summarize one of the main obtained results in Fig.…”

Experimental study of precisely selected evaporation chains in the decay of excited Mg25

“…Typically, the method consists of investigating the various decay paths of compound nuclei formed in fusion reactions, selected as accurately as possible, to evidence deviations from the prediction of pure statistical models, which are based on average phase-space considerations and do not include, in their "standard" implementations, the possibility that the branching ratio toward α emission might be affected by a possible α-structure of the parent state. The main focus in our previous works was on the fusion reactions 12 C + 12 C, producing 24 Mg nuclei at E * = 61.4 MeV excitation energy [4,5]. Although we there verified a quite nice agreement of many decay features with the predictions of a statistical model, we observed some deviations in the channels involving the evaporation of only α particles.…”

“…From the analysis of the 12 C+ 12 C reaction presented in Refs. [4,5], we estimated that the the 24 Mg BR for 6α channel is BR 6α = 3‰. So the total number of 24…”

“…In this work we give a further contribution to the experimental study of light excited systems, following the approach of our previous papers [4,5,10,17]. Typically, the method consists of investigating the various decay paths of compound nuclei formed in fusion reactions, selected as accurately as possible, to evidence deviations from the prediction of pure statistical models, which are based on average phase-space considerations and do not include, in their "standard" implementations, the possibility that the branching ratio toward α emission might be affected by a possible α-structure of the parent state.…”