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Register a new userUnbound states in $^{12}$C populated by $gamma$-decay of the $(J^{pi},T) = (2^+,1)$ 16.11 MeV state
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The reaction $^{11}textrm{B}+p$ has been used to populate the $(J^pi,T) = (2^+,1)$ state at an excitation energy of 16.11 MeV in $^{12}$C. $gamma$-decay to unbound states in $^{12}$C are identified from analysis of the decay of the populated daughter states. Due to a new technique, $gamma$-decay to the 10.8 MeV 1$^-$ state is observed for the first time, and transitions to the 9.64 MeV (3$^-$) and 12.71 MeV (1$^+$) are confirmed. Unresolved transitions to natural parity strength at 10 MeV and 11.5-13 MeV are also observed. For all transitions partial widths are deduced
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The 3$alpha$ decay of the 16.62,MeV (2$^-$, T=1) resonance in $^{12}$C has been studied for nearly a century starting with one of the first nuclear reaction studies at the Cavendish Laboratory in the 1930s. In the hitherto latest study published a decade ago a model based on earlier work from the 1960s was found to give a good account of a set of inclusive data. This model describes the decay as an l=3 $alpha$-particle populating the 2$^+$ state of $^8$Be. Here we provide new exclusive data on the 3$alpha$ decay of the 16.62,MeV resonance, and demonstrate that the decay is best described by a model with predominantly l=1 emission with an admixture of l=3.
Total absorption spectroscopy was used to investigate the beta-decay intensity to states above the neutron separation energy followed by gamma-ray emission in 87,88Br and 94Rb. Accurate results were obtained thanks to a careful control of systematic errors. An unexpectedly large gamma intensity was observed in all three cases extending well beyond the excitation energy region where neutron penetration is hindered by low neutron energy. The gamma branching as a function of excitation energy was compared to Hauser-Feshbach model calculations. For 87Br and 88Br the gamma branching reaches 57% and 20% respectively, and could be explained as a nuclear structure effect. Some of the states populated in the daughter can only decay through the emission of a large orbital angular momentum neutron with a strongly reduced barrier penetrability. In the case of neutron-rich 94Rb the observed 4.5% branching is much larger than the calculations performed with standard nuclear statistical model parameters, even after proper correction for fluctuation effects on individual transition widths. The difference can be reconciled introducing an enhancement of one order-of-magnitude in the photon strength to neutron strength ratio. An increase in the photon strength function of such magnitude for very neutron-rich nuclei, if it proved to be correct, leads to a similar increase in the (n,gamma) cross section that would have an impact on r-process abundance calculations.
The reaction $^{11}B+p$ has been used to populate the $(J^{pi},T)=(2^+,1)$ state at an excitation energy of 16.11 MeV in $^{12}$C, and the breakup of the state into three $alpha$ particles has been studied in complete kinematics. A two-step breakup model which includes interference effects is found to provide the most accurate description of the experimental data. The branching ratio to the ground state of $^8$Be is determined to be 5.1(5)% in agreement with previous findings, but more precise by a factor of two, while the decay to the first-excited state in $^8$Be is found to be dominated by $d$-wave emission.
Unbound states of $^{10}$C nuclei produced as quasi-projectiles in $^{12}$C+$^{24}$Mg collisions at E/A = 53 and 95 MeV are studied with the Indra detector array. Multi-particle correlation function analyses provide experimental evidence of sequential de-excitation mechanisms through the production of intermediate $^{9}$B, $^{6}$Be and $^{8}$Be unbound nuclei. The relative contributions of different decay sequences to the total decay width of the explored states is estimated semi-quantitatively. The obtained results show that heavy-ion collisions can be used as a tool to access spectroscopic information about exotic nuclei.
Multiple alpha coincidence and correlations are studied in the reaction $^{12}$C+$^{12}$C at 95 MeV for fusion-evaporation events completely detected in charge. Two specific channels with Carbon and Oxygen residues in coincidence with $alpha$-particles are addressed, which are associated with anomalously high branching ratios with respect the predictions by Hauser-Feshbach calculations. Triple alpha emission appears kinematically compatible with a sequential emission from a highly excited Mg. The phase space distribution of $alpha$-$alpha$ 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 $alpha$ emission of $^{24}$Mg at excitation energies well above the threshold for $6-alpha$ decay.
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