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7 pags., 5 figs., 1 app., The space and time configurations of the dissociation of He into He+n+n, on C and Pb targets, have been explored simultaneously for the first time. The final-state interactions in the n-n and He-n channels are successfully described within a model that considers independent emission of neutrons from a Gaussian volume with a given lifetime. The dissociation on C target exhibits a dominant sequential decay through the ground state of He, consistent with neutrons being emitted from a Gaussian volume of fm with a n-n delay in the sequential channel of 1400 400 fm/c, in agreement with the lifetime of He. The lower-statistics data on Pb target correspond mainly to direct breakup, and are well described using the n-n volume measured, without any n -n delay. The validity of the phenomenological model used is discussed., The support provided by the technical staff of LPC and the LISE crew is gratefully acknowledged, as are the efforts of the GANIL cyclotron operation team for providing the primary beam. We also wish to express our appreciation for the vital contributions made by our late colleague and friend Jean-Marc Gautier to all the CHARISSA+DEMON experiments undertaken by our collaboration.

International audience; Nuclear fission is a complex process, still not yet well described by microscopic models, and its main observables are difficultto measure with accuracy. Following the capture of a thermal neutron the compound nucleus fissions in two fragments. Mostof the energy of the process is transferred in kinetic energy, whereas the nuclei are let in few tens of MeV excited states. Thisexcitation energy is then released, the majority of it within less than some nanoseconds, by the evaporation of a few neutronsand the emission of -rays in cascade.To overcome the low accuracy of microscopic models in the prediction of fission observables, nuclear technology relies onlibraries of evaluated data and semi-empirical models, like the GEF model for fission yield evaluations. Such a strategy requestssystematic and accurate experimental data on the few possible observables. Here we will present the advantages of studyingyields of fragment correlated pairs and their de-excitations using an array of high-resolution -ray detectors directly placedaround an actinide target irradiated by a thermal or cold neutron beam. Such a setup was installed at ILL in 2012 and 2013(EXILL) and campaigns were performed with 235U and 241Pu targets. This study is largely motivated by the future installation of apermanent -ray detector array at the ILL, which will be coupled to fission fragment detectors in a first construction phase and afragment separator in a second phase (FIPPS).An important outcome of EXILL data is the observation of the -ray cascade occurring in both fission fragments with an unambiguousdetermination of the fragments. The cascade is directly linked with the angular momentum of the fragments afterscission, which is one of the less precise and less understood properties. With the development of new simulation codes for theneutron evaporation and the -ray cascade like FIFRELIN or KEWPIE, systematic studies and comparisons with the large amountof experimental data resulting from double and triple gamma-ray coincidence analysis become possible. Preliminary results onthe gamma–ray cascades measured in the well produced Kr and Ba fragments and comparisons with FIFRELIN simulations willbe presented.

The effects of the entrance channel and shell structure on the experimental evaporation residues have been studied by analyzing the 32S + 182W, 48Ti + 166Er and 60Ni + 154Sm reactions leading to 214Th*; the 40Ar + 181Ta reaction leading to 221Pa*; the 48Ca + 243Am, 248Cm, 249Cf reactions leading to the 291115, 296116 and 297118 superheavy compound nuclei, respectively. The fusion mechanism and the formation of evaporation residues of heavy and superheavy nuclei have been studied. In calculations of the excitation functions for capture, fusion and evaporation residues we used such characteristics as mass asymmetry of nuclei in the entrance channel, binding energies and shape of colliding nuclei, potential energy surface, driving potential, partial-fusion cross-sections and survival probability of the compound nucleus, $\Gamma_{\rm n} / \Gamma_{\rm f}$ ratio at each step along the de-excitation cascade of the compound nucleus. The calculations have allowed us to make useful conclusions about the mechanism of the fusion-fission process, which is in competition with the quasifission process, and the production of the evaporation residues.

Nuclear dissipation in capture reactions is investigated using backtracing. Combining the analysis procedure with dynamical models, the difficult and long-standing problem of competition and mixing of quasi-fission and fusion-fission is solved for the first time. At low excitation energy a new protocol able to handle low statistics data gives access to the prescission neutron multiplicity in two different systems 48 Ca +208 Pb, Pu . The results are in agreement with a domination of fusion-fission in the case of 256 No and an equal mixing of quasi-fission and fusion-fission in the case of Z=114. The nature of the relevant dissipation is determined as one-body dissipation.

The process of fusion-fission of heavy and superheavy nuclei (SHE) with Z = 82-122 formed in the reactions with Ca-48 and Fe-58 ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) and at the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multidetector DEMON. As a result of the experiments, mass and energy distributions (MED) of fission fragments ; fission, quasifission, and evaporation residue cross sections ; and multiplicities of neutrons and gamma-quanta and their dependences on the mechanism of formation and decay of compound systems have been studied.