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Register a new userProbing the statistical decay and alpha-clustering effects in 12c+12c and 14n+10b reactions
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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.
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Dissipative 12C+12C reactions at 95 MeV are fully detected in charge with the GARFIELD and RCo apparatuses at LNL. A comparison to a dedicated Hauser-Feshbach calculation allows to select events which correspond, to a large extent, to the statistical evaporation of highly excited 24Mg, as well as to extract information on the isotopic distribution of the evaporation residues in coincidence with their complete evaporation chain. Residual deviations from a statistical behaviour are observed in alpha yields and attributed to the persistence of cluster correlations well above the 24Mg threshold for 6 alphas decay.
The fusion reactions 12C(12C,a)20Ne and 12C(12C,p)23Na have been studied from E = 2.10 to 4.75 MeV by gamma-ray spectroscopy using a C target with ultra-low hydrogen contamination. The deduced astrophysical S(E)* factor exhibits new resonances at E <= 3.0 MeV, in particular a strong resonance at E = 2.14 MeV, which lies at the high-energy tail of the Gamow peak. The resonance increases the present non-resonant reaction rate of the alpha channel by a factor of 5 near T = 8x10^8 K. Due to the resonance structure, extrapolation to the Gamow energy E_G = 1.5 MeV is quite uncertain. An experimental approach based on an underground accelerator placed in a salt mine in combination with a high efficiency detection setup could provide data over the full E_G energy range.
New experimental data for the 12C+12C reaction have been measured in the centre-of-mass energy range E_{c.m.}= 40 to 60 MeV. Excitation functions for a number of single and mutual $^{12}$C inelastic channels have been measured which include the 0_{gs}, 2_{1}^+, 0_{2}^+, 3_{1}^-, and 4$_1^+$ 12C states. All of the reactions display largely unstructured excitation functions over this energy range. The absence of further resonances in this energy region for the 12C(12C,2C[3_1^-])12C[3_1^-$] reaction confirms theoretical predictions of the termination of the band of resonances found at lower centre-of-mass energies in this channel.
The fragmentation of quasi-projectiles from the nuclear reaction $^{40}Ca$+$^{12}C$ at 25 MeV/nucleon was used to produce excited states candidates to $alpha$-particle condensation. The methodology relies on high granularity 4$pi$ detection coupled to correlation function techniques. Under the assumption that the equality among the kinetic energies of the emitted $alpha$-particles and the emission simultaneity constitutes a reliable fingerprint of $alpha$ condensation, we identify several tens of events corresponding to the deexcitation of the Hoyle state of $^{12}$C which fulfill the condition.
Existing measurements of the angular distributions of the ground-state to ground-state transitions of the 12C(d,p)13C and 13C(p,d)12C neutron-transfer reactions have been analyzed systematically using the Johnson-Soper adiabatic and distorted-wave theories. When using a consistent set of physical inputs the deduced spectroscopic factors are consistent to within 20% for incident deuteron energies from 6 to 60 MeV. By contrast, original analyses of many of these data quoted spectroscopic factors that differed by up to a factor of five. The present analysis provides an important reference point from which to assess the requirements of future spectroscopic analyses of transfer reactions measured in inverse kinematics using rare nuclei.
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