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International audience; Low-lying states of Cd98 have been populated by the two-nucleon removal reaction (In100,Cd98+γ) and studied using in-beam γ-ray spectroscopy at the Radioactive Isotope Beam Factory at RIKEN. Two new γ transitions were identified and assigned as decays from a previously unknown state. This state is suggested to be based on a π1g9/2−12p1/2−1 configuration with Jπ=5−. The present observation extends the systematics of the excitation energies of the first 5− state in N=50 isotones toward Sn100. The determined energy of the 5− state in Cd98 continues a smooth trend along the N=50 isotones. The systematics are compared with shell-model calculations in different model spaces. Good agreement is achieved when considering a model space consisting of the π(1f5/2, 2p3/2, 2p1/2, 1g9/2) orbitals. The calculations with a smaller model space omitting the orbitals below the Z=38 subshell could not reproduce the experimental energy difference between the ground and first 5− states in N=50 isotones, because proton excitations across Z=38 subshell yield a large amount of correlation energy that lowers the ground states.

International audience; Background: The phenomenon of fusion hindrance may have important consequences on the nuclear processes occurring in astrophysical scenarios, if it is a general behavior of heavy-ion fusion at extreme subbarrier energies, including reactions involving lighter systems, e.g., reactions in the carbon and oxygen burning stages of heavy stars. The hindrance is generally identified by the observation of a maximum of the S factor vs energy. Whether there is an S-factor maximum at very low energies for systems with a positive fusion Q value is an experimentally challenging question. Purpose: Our aim has been to search for evidence of fusion hindrance in C12+Mg24 which is a medium-light system with positive Q value for fusion, besides the heavier cases where hindrance is recognized to be a general phenomenon. C12+Mg24 is very close to the O16+O16 and C12+C12 systems that are important for the late evolution of heavy stars. Methods: The experiment has been performed in inverse kinematics using the Mg24 beam from the XTU Tandem accelerator of LNL in the energy range 26–52 MeV with an intensity of 4–8 pnA. The targets were C12 evaporations 50μg/cm2 thick, isotopically enriched to 99.9%. The fusion-evaporation residues were detected at small angles by a E-ΔE-ToF detector telescope following an electrostatic beam deflector. Results: Previous measurements of fusion cross section for C12+Mg24 were limited to above-barrier energies. In the present experiment the excitation function has been extended down to ≃15μb and it appears that the S factor develops a clear maximum vs energy, indicating the presence of hindrance. This is the first convincing evidence of an S factor maximum in a medium-light system with a positive fusion Q value. These results have been fitted following a recently suggested method and a detailed analysis within the coupled-channels model that has been performed using a Woods-Saxon potential and including the ground state rotational band of Mg24. The coupled-channels calculations give a good account of the data near and above the barrier but overpredict the cross sections at very low energies. Conclusions: The hindrance phenomenon is clearly observed in C12+Mg24, and its energy threshold is in reasonable agreement with the systematics observed for several medium-light systems. The fusion cross sections at the hindrance threshold show that the highest value (σs=1.6mb) is indeed found for this system. Therefore it may even be possible to extend the measurements further down in energy to better establish the position of the S-factor maximum.

International audience; The double-gamma decay is a second order electromagnetic process where two photons are emitted simultaneously. It is characterized by low branching ratios, making its measurement interesting both theoretically and also experimentally. Although this process has been already observed in the past, a recent publication claimed its observation in competition with the single gamma decay. A measurement of this process with the AGATA spectrometer (Advanced GAmma Tracking Array) will deliver more detailed results. A test of feasibility of this challenging measurement has been performed through GEANT4 simulations of the decay of the 137Ba isotope. Particular emphasis is placed on the tracking algorithm which allows to reconstruct a scattering gamma-ray event based on the position and energy of every interaction point within the AGATA germanium detector.