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Alpha-particle spectrum from the 32S(12C,Ot)40Ca reaction at a bombarding energy of 30 MeV. The excitation energies shown were calculated from the 7.5 and 15 ° spectra of the present study and may include uncertainties as large as :e25 keV. The shaded group corresponds to the 160(12C,~) transition to the 4.12 MeV 4 + level of 24Mg. Other ~-particle groups resulting from impurities were either too weak to be identified or occur at high excitations where there is a large density of states. Previously suggested [1-4] 4p-4h and 8p-Sh states are labeled. at 3.74 MeV and the 5-state at 4.49 MeV a r e both weakly excited. A l s o , the ground state is e x t r e m e l y weak. The weak population of the ground state is e x p e c t e d for a d i r e c t p r o c e s s , as is d i s c u s s e d later. A t r i p l e t of s t a t e s is known to e x i s t n e a r 5.25 MeV-at 5.21, 5.25 and 5.28 MeV. Only two peaks a r e o b s e r v e d at this e x c i t a t i o n e n e r g y in the s p e c t r u m , and t h e i r s e p a r a t i o n is c o n s i s t e n t only with an identification of the two peaks as c o r r e s p o n d i n g to the known 5.21 and 5.28 MeV s t a t e s. Thus, the 0 +, 2 +, and 4 + m e m b e r s of the s u g g e s t e d [1,2] 4p-4h band (at 3.35, 3.90, and 5.28 M e ¥ , r e s p e c t i v e l y ) a r e populated m o r e s t r o n g l y than any o t h e r state below E x = 5.5 MeV. If the state we o b s e r v e at E x = 5.61 MeV is indeed the 2 + state with an e x c i t a t i o n e n e r g y of 5.63 MeV [1] (as is v e r y likely, s i n c e our e x c i t ation e n e r g i e s for the s t a t e s n e a r 5.2 MeV a r e all too low by about the s a m e amount), then the sugg e s t e d 8p-Sh s t a t e s having jTr = 0 + and 2 + a r e even m o r e s t r o n g l y excited than the 4p-4h s t a t e s of the s a m e spins. The c r o s s s e c t i o n s for these s t a t e s a r e c o m p a r e d in table 2. If the state we o b s e r v e at 6.54 MeV is the 4 + m e m b e r of the
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Multiple alpha coincidences and correlations are studied in the reaction 12C+12C at 95 MeV for fusion–evaporation events completely detected in charge. Two specific channels with carbon and oxygen residues in coincidence with α −particles are addressed, which are associated with anomalously high branching ratios with respect to the predictions of Hauser–Feshbach calculations. Triple alpha emission appears kinematically compatible with a sequential emission from a highly excited Mg. The phase space distribution of α − α coincidences suggests a correlated emission from a Mg compound, leaving an oxygen residue excited above the threshold for neutron decay. These observations indicate a preferential α emission of 24Mg at excitation energies well above the threshold for 6 − α decay.
The $^{12}$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 $\alpha$-clustering effects. These
channels are studied in further details in the second paper of the series.
$\alpha$-clustering study since the pioneering discovery of $^{12}$C+$^{12}$C
molecular resonances half a century ago. Our knowledge on physics of nuclear
molecules has increased considerably and nuclear clustering remains one of the
most fruitful domains of nuclear physics, facing some of the greatest
challenges and opportunities in the years ahead. The occurrence of "exotic"
shapes in light $N$=$Z$ $\alpha$-like nuclei is investigated. Various
approaches of the superdeformed and hyperdeformed bands associated with
quasimolecular resonant structures are presented. Evolution of clustering from
stability to the drip-lines is examined: clustering aspects are, in particular,
discussed for light exotic nuclei with large neutron excess such as
neutron-rich Oxygen isotopes with their complete spectrocopy.
Since the pioneering discovery of 12C+12C molecular resonances half a century ago,
a great deal of research work has been undertaken in the alpha-clustering study. Our knowledge on the physics of nuclear molecules has increased considerably and nuclear clustering remained one of the most fruitful domains of nuclear physics, facing some of the greatest challenges and opportunities in the years ahead. In this work, the occurrence of \exotic" shapes in light N=Z alpha-like nuclei is investigated. Various approaches of the superdeformed and hyperdeformed bands associated with quasimolecular resonant structures are presented. Clustering aspects are also briefy discussed for light nuclei with neutron excess trough very recent results on neutron-rich Oxygen isotopes.
