Search

Starting from experimental studies on alpha-clustering in excited self-conjugate nuclei (from $^{16}$O to $^{28}$Si), temperature and density conditions for such a clustering are determined. Measured temperatures have been found in the range of 5.5 - 6.0 MeV whereas density values of 0.3 - 0.4 times the saturation density are deduced, i.e., 0.046 to 0.062 $fm^{-3}$. Such a density domain is also predicted by constrained self-consistent mean field calculations. These results constitute a benchmark for alpha clustering from self-conjugate nuclei in relation to descriptions of stellar evolution and supernovae., 7 pages, 3 figures. arXiv admin note: text overlap with arXiv:1602.05827, arXiv:1603.01114

In the next few years the existing superconducting cyclotron will be upgraded to provide ion beams with power up to 10 kW. A new FRAgment In-flight SEparator (FRAISE) has been proposed to take advantage of the higher beam power. Due to the constraint of the experimental hall shielding walls we expect to run the facility with power no higher than 3 kW. The mass of the ion available as primary beam will be lower than 70 amu. FRAISE could deliver radioactive ion beam at three experimental facilities: the magnetic spectrometer MAGNEX, the multi detector CHIMERA and the general purpose scattering chamber GIRA. Many studies will benefit from the new set-up such as: Structure of exotic nuclei, Clustering, Isospin in reaction dynamics, nuclear astrophysics (THM indirect measurement), collective resonance (GMR, GDR, PYGMY), etc.

We present results of barrier distribution measurements for $^{24}\mathrm{Mg}+^{90,92}\mathrm{Zr}$ systems by the backscattering method. The measurements were done at near-barrier beam energies of 68--88.5 MeV (in the laboratory frame) at six angles. A strong discrepancy between experimental results and the predictions of the standard coupled channels calculations was observed. To test the hypothesis that this discrepancy may be due to partial energy dissipation caused by coupling to many target noncollective levels, we performed calculations using the coupled channels plus random matrix theory ($\mathrm{CC}+\mathrm{RMT}$) model. The comparison of calculations with experimental results gives qualitative support of the hypothesis; however, quantitatively the agreement is not as good as in the case of the $^{20}\mathrm{Ne}$ projectile.

It is discussed the dynamics of Isospin equilibration in reactions involving the production of Intermediate Mass Fragment (IMF) in the mid-rapidity region. The investigation proceeds through the measurements of the reduced value of the total dipolar signal obtained from the measured velocities and charges of all fragments produced in the collision 48 Ca +27 Al at 40 MeV/nucleon. Preliminary experimental results, along with the comparison with CoMD-III model calculations for different density functionals related to the symmetry energy, are presented.

International audience; The emission probability of Intermediate Mass Fragments (IMFs) in non-central reactions has been investigated in collisions of heavy $^{124}\hbox {Xe}$ projectiles with the two different medium-mass targets of $^{64}\hbox {Ni}$ and $^{64}\hbox {Zn}$ at the laboratory energy of 35 A MeV. The two colliding systems differ only for the target atomic number Z and, consequently, for the isospin N/Z ratio. The probability of IMFs emission from the projectile-like fragment has been measured, showing an enhancement of the IMFs emission for the neutron rich $^{64}\hbox {Ni}$ target. Most of the observed projectile break-up yield is associated with the production of only one IMF, that is, a quasi-binary splitting of projectile in two fragments in a broad range of charge asymmetry. For the events with one IMF, the relative contributions of the dynamical and statistical emissions have been evaluated. We find an enhancement of dynamical break-up probability for the neutron rich target with respect to the neutron poor one. The analysis suggests influence of the target isospin in inducing the dynamical break-up of projectile-like fragments. The new data have been also compared with previous published results of $^{112,124}\hbox {Sn}$ + $^{58,64}\hbox {Ni}$ systems, in order to disentangle between isospin effects against system-size effects on the emission probability. The comparisons between previous and new data suggest that the dynamical break-up is determined by the N/Z content of both projectile and target; for the cases here investigated, the influence of the system size on the dynamical emission probability can be excluded.

Binary collisions of either stable or radioactive heavy ions at Fermi energies allow to study the nuclear reaction mechanisms under dynamical conditions of non-equilibrium and the formation of transient pieces of nuclear matter of very short mean life times at sub-normal density. An important role in the evolutionary phase of the collision is played by the gradient of the nuclear density affecting the isospin asymmetry of the reaction products by typical transport phenomena such as the isospin diffusion and drift. Experimental determination of the value of the nuclear matter density in the early phase of the collision is a crucial step towards understanding the underlying mechanism responsible for the production of clusters. In this paper a method for evaluating the nuclear density in semi-peripheral collisions in the reaction $$^{124}Sn + ^{64}Ni$$ at 35 MeV/nucleon as studied with the CHIMERA multi-particle detector is described.

The γ-decays of 12C excited levels (the Hoyle state 0+ at 7.65 MeV and the 9.64 MeV 3) are essential for its production in the universe. We present here a new attempt to precisely measure such γ-decay probabilities. The measurement was performed at INFN-LNS in Catania using the 4π CHIMERA multidetector. In order to measure these low probability decay-channels we performed 4-fold coincidence measurements. The 12C target nuclei were excited by using a beam of 64 MeV α-particles produced by the Superconducting Cyclotron (CS) of INFN-LNS. The scattered α-particles and the 12C recoils were detected and identified by? E-E and ToF methods using CHIMERA telescopes. The two emitted γ-rays in the decay chain were detected and identified by using the second stage of the telescopes, CsI(Tl) scintillators, by means of fast-slow and rise time techniques. Kinematics and energy-momentum conservation laws were used to constrain the data analysis. Also the 3-α decay channel probability was measured. Such a simultaneous measurement of all known decay channels was useful to reduce the systematic errors. Preliminary results of the data analysis are reported.

With the advent of the new radioactive beam facilities it is necessary to develop neutron detection systems integrated with charged particle ones. The integration of the neutron signal, especially in using neutron rich beams, becomes a mandatory requirement in order to study the property of the nuclear matter in extreme conditions. For this reason new detectors using new materials have to be built. In this contribution, some new results about the efficiency estimation and the cross talk problem studied through GEANT4 simulations, related to the NArCoS project, will be described with the aim to design a new detector of both good energy and angular resolution. The detection of neutrons and charged particles in the same elementary detection cell is envisaged.

We describe the use of the 4tt CHIMERA charged particle detector as a large efficiency y-ray detector. The CsI(Tl) stage of the CHIMERA telescope is used to detect and identify y-rays. The high detection efficiency and the sufficient energy resolution guaranteed by CsI(Tl) allows us to use the detector for the study of rare decays. Two examples are reported: the low probability gamma decay (68Ni; the measurement of the gamma decay probability of excited levels of 12C as the Hoyle state at 7.65 (∼10−4) MeV and the 3- level at 9.64 MeV (∼107), both important for the Carbon production in stars. Future experiments made possible at INFN-LNS by the availability of the new fragment separator FRAISE are also outlined.

The motivation of the present paper is to study the performance of EJ 299-33 scintillator in online and off-line analysis in high rate scattering for nuclear reaction experiments performed with heavy ions. An experiment was carried out inside the CHIMERA chamber using 24Mg beams at 71.5 MeV and 81 MeV impinging on 92ZrO2 target. The plastic scintillator was backed by a photomultiplier tube and the anode pulses were digitized through 100 MHz GET electronics for the purpose of pulse shape discrimination (PSD) studies. Performances of the plastic scintillator have been tested with respect to PSD capabilities and energy spectra analysis under beam irradiations in a high background environment.

High energy gamma-rays from the 116Sn + 24Mg reaction at 23A MeV were measured using the MEDEA detector at LNS – INFN Catania. Combining this new data with previous measurements yields a detailed view of the quenching of the Giant Dipole Resonance as a function of excitation energy in nuclei of mass A in the range 120÷132. The transition towards the disappearance of the dipole strength, which occurs around 230 MeV excitation energy, appears to be remarkably sharp. Current phenomenological models give qualitative explanations for the quenching but cannot reproduce its detailed features. Keywords: Giant Dipole Resonance, Hot nuclei, Fusion reactions, Statistical Model

FARCOS is a modular detection system intended to boost the capacity of 4π detectors towards correlation measurements. The final FARCOS system will be composed of 20 telescopes, each formed by two Si layers of 32-ch orthogonal Double Sided Silicon Strip Detectors and one calorimeter stage composed by 4 CsI(Tl) tronco-pyramidal scintillator crystals readout by a Si photodiode. The paper focuses on the first application of the FARCOS detection array in the present configuration of 10 telescopes in a real experiment, the CHIFAR experiment and discusses the main instrumental features relevant for the experiments.

International audience; Background: Near-threshold α-clustered states in light nuclei have been postulated to have a structure consisting of a diffuse gas of α particles which condense into the 0s orbital. Experimental evidence for such a dramatic phase change in the structure of the nucleus has not yet been observed. Purpose: To understand the role of α condensation in light nuclei experimentally. Method: To examine signatures of this α condensation, a compound nucleus reaction using 160-, 280-, and 400-MeV O16 beams impinging on a carbon target was used to investigate the C12(O16,7α) reaction. This permits a search for near-threshold states in the α-conjugate nuclei up to Mg24. Results: Events up to an α-particle multiplicity of seven were measured and the results were compared to both an extended Hauser-Feshbach calculation and the Fermi breakup model. The measured multiplicity distribution exceeded that predicted from a sequential decay mechanism and had a better agreement with the multiparticle Fermi breakup model. Examination of how these 7α final states could be reconstructed to form Be8 and C12(02+) showed a quantitative difference in which decay modes were dominant compared to the Fermi breakup model. No new states were observed in O16, Ne20, and Mg24 due to the effect of the N-α penetrability suppressing the total α-particle dissociation decay mode. Conclusion: The reaction mechanism for a high-energy compound nucleus reaction can only be described by a hybrid of sequential decay and multiparticle breakup. Highly α-clustered states were seen which did not originate from simple binary reaction processes. Direct investigations of near-threshold states in N-α systems are inherently impeded by the Coulomb barrier prohibiting the observation of states in the N-α decay channel. No evidence of a highly clustered 15.1-MeV state in O16 was observed from [Si★28,C12(02+)]O16(06+) when reconstructing the Hoyle state from three α particles. Therefore, no experimental signatures for α condensation were observed.

Main features of fragments produced in 58Ni+40Ca and 58Ni+48Ca systems at 25 AMeV, collected by Chimera multidetector at INFN Laboratori Nazionali del Sud (Italy), are analysed in order to study properties of moderately excited systems (Ex=2-5 AMeV) formed in central collisions. By means of correlations between specific global variables, sensitive to the centrality of the collision, a stringent selection of Fusion-Evaporation residues, Multifragmentation sources and their decay products has been performed. The influence of the isospin contents of the systems on the reaction mechanism is carefully investigated and relevant observables such as isospin asymmetry N/Z or charge and mass of fragments, are discussed in order to probe the fragmentation path, characterised by short living ( ∼ 100fm/c) low density states of nuclear matter out of equilibrium. Preliminary comparisons with predictions of the BLOB model, in a semi-classical mean field framework, are presented, investigating cluster production emerging from the occurrence of low-density instabilities in central collisions.

The 0 2 + Hoyle state and few other excited levels of 12C are fundamental for the production of carbon in the universe. In particular, the γ decay branching ratio is of utmost importance, being the only way to produce a carbon at the ground state. For the purpose to precisely investigate the decay mechanism of such states we conducted an experiment, at Laboratori Nazionali del Sud-Istituto Nazionale di Fisica Nucleare (INFN-LNS), using the reaction α + 12 C at 64 MeV. We used the 4π CHIMERA detector to detect both α and γ 12 C decay channels. Details of the experiment and preliminary results are discussed in the paper.

International audience; In heavy ion collisions at low energy (E/A < 10–15 MeV/nucleon) the N/Z ratio in the entrance channel is closely related to the isospin degree of freedom and can influence the reaction mechanisms and consequently the production of the fragments in the exit channel. We analyse the fragment production cross sections in the reactions$^{86}$Kr +$^{48}$Ca and$^{78}$Kr +$^{40}$Ca , at the laboratory energy of 10 MeV/nucleon. The experiment was conducted at the INFN Laboratori Nazionali del Sud in Catania, by using the $ 4\pi$ detector CHIMERA. For the two reactions, elastic scattering measurements are performed to extract the normalization factor used to evaluate the absolute cross sections. Velocity and energy spectra, mass and charge distributions, as well as dynamic features of reaction products, are studied. The study of the characteristics of mass and charge distributions, energy and velocity spectra of the reaction products shows mainly a relaxed component, related to fusion reaction followed by evaporation or binary decay. Nevertheless signals ascribable to a non equilibrated component are present. Structure effects are evident in the staggered shape of emitted fragments cross sections and are more pronounced in the neutron poor system. The analysis highlights clear differences for the two systems in the contributions arising from different reaction mechanisms. Besides, a study of the overall influence from the entrance channel energy is performed. Comparisons to DNS (DiNuclear System) and GEMINI++ models are reported. The data analysis indicates a slightly higher fusion-evaporation cross section and a strongly pronounced probability of fission-like processes for the neutron poor system with respect to the neutron rich one. The neutron enrichment seems thus to limit the formation of the composite system and to inhibit the fission decay channel.

In this work, we present a recent study concerning the break-up of the Projectile-Like (PLF) into two fragments, following more violent deep-inelastic collisions in the reactions 78Kr + 40Ca and 86Kr + 48Ca at 10 A MeV, realized at INFN-Laboratori Nazionali del Sud by using the 4π multi detector CHIMERA. For these systems, we have already analyzed the fusion-evaporation and fission-like processes. A selection method has been developed, in order to discriminate PLF break up events from those due to other mechanisms which populate the same region of the phase- space. A preference for PLF aligned break-up, along the direction of the PLF-TLF separation axis with the light fragment emitted in the backward part, has been put in light, suggesting the presence of dynamical effects. Also a comparison between the neutron-rich 86Kr + 48Ca and neutron-poor 78Kr + 40Ca systems is presented, to put in evidence the isospin role in these processes.

The FARCOS (Femtoscope ARray for Correlation and Spectroscopy) collaboration is finally going to instrument the first batch of 10-12 telescopes. They are capable of reconstructing the particle’s momentum with a high degree of precision and of performing correlation measurements of Light Charged Particles (LCPs) and of LCPs and Intermediate Mass Fragments thanks to the very good energy and angular and resolution. Each telescope features a sensitive area of 6.4 × 6.4 cm2 and is composed of three detection stages: two Si layers and a CsI(Tl) calorimeter. The FARCOS cluster modularity allows the arrangement in different configurations, depending on the physics case one wants to address. The final system will be a modular assembly of 20 telescopes. The total number of readout channels for the final FARCOS system is 2560 channels for the silicon layers and 80 channels for the scintillators. In this paper, we focus on the FARCOS basic module and system architecture and illustrate its performance as assessed in test beams in true experimental conditions.

With the advent of radioactive beams there is a quest for developing novel experimental methods and instruments able to cope with beam characteristics to extract spectroscopic information and to study novel nuclear reaction mechanisms. The tendency is towards Digital Pulse Shape Acquisition since it allows one to fully profit of the information encoded in the detector output response. Even if the convenience of driving the signals over differential pairs to preserve signal integrity in noise environment when long cables are used is evident, there is a lack of digitizing electronics that features a differential input. To this aim we designed, build and qualified an antialiasing module that provides 256 channel antialiasing filter with selectable parameters and differential input to be coupled with the GET – Generic Electronic System for TPCs - backend electronics. The contribution focuses on the board design, layout and performance measured both as a standalone circuit and during on-beam experiments.

International audience; The study of nuclei properties and of collision dynamics is a very active research field whose result have implications in different domains as for example astrophysics. The present and future facilities delivering radioactive ion beams with high intensity allow to extend these studies in the region far from the stability valley. New insight has thus been found on the effects of neutron richness on reaction mechanisms as well as on nuclear structure and nuclear matter properties, as for instance, the role of symmetry energy term of the nuclear Equation of State. The presence of diverse reaction products demands for highly performing and very specialized devices, also able to disentangle among different mechanisms, from fast dynamical processes to statistical emission from equilibrated sources. Numerous studies of the effects of N/Z ratio on fusion and associated processes can be found at different energies, together with many examples of the influence of neutron richness on the reaction time scale and the competition between equilibrated and prompt processes. A survey of very recent findings obtained with the CHIMERA and FARCOS devices is presented.

It is known that the low-energy E1 strength, known as the Pygmy Dipole Resonance (PDR), can be excited by both isovector and isoscalar probes. In this work, we report on the results of an experiment, carried out at the LNS-INFN in Catania, with the aim to study the Pygmy Dipole Resonance induced in the 68Ni nucleus through the interaction with a 12C isoscalar target. The CHIMERA multidetector and the FARCOS array were used to detect, respectively, γ rays and charged particles. Details on the experimental set-up, data analysis and results are reported.

International audience; Preliminary analysis of the Hoyle-Gamma experiment is presented, where simultaneous gamma-particles detection for the α + 12C → α + (12C* + γ) reaction is used to suppress the background various orders of magnitude. This will allow us to measure very small Γ partial widths of 12C. Details of the method, the implementation and CHIMERA software analysis are presented as well as preliminary results.

International audience; The study of cluster states in neutron-rich Be and C isotopes is a subject of interest in Nuclear Physics. These states should be characterized by high deformation where α-clusters are bounded by valence neutrons. We performed a spectroscopic study of 10Be and 16C isotopes via projectile break-up reactions, by using radioactive beams produced at the INFN-LNS FRIBs facility and the Chimera 4π array. The possible evidence of a new 10Be state at 13.5 MeV excitation energy was found in the 6He+4He disintegration channel. The spectroscopy of 16C was studied via the 6He+10Be break-up channel; in this case we found the indication of a possible new state at about 20.6 MeV.

In nuclear reactions at Fermi energies two and multi particles intensity interferometry correlation methods are powerful tools in order to pin down the characteristic time scale of the emission processes. In this paper we summarize an improved application of the fragment-fragment correlation function in the specific physics case of heavy projectile-like (PLF) binary massive splitting in two fragments of intermediate mass(IMF). Results are shown for the reverse kinematics reaction 124 Sn+64 Ni at 35 AMeV that has been investigated by using the forward part of CHIMERA multi-detector. The analysis was performed as a function of the charge asymmetry of the observed couples of IMF. We show a coexistence of dynamical and statistical components as a function of the charge asymmetry. Transport CoMD simulations are compared with the data in order to pin down the timescale of the fragments production and the relevant ingredients of the in medium effective interaction used in the transport calculations.

The present study has been carried out in order to investigate about the possibility of using EJ 299-33 scintillator in a multi-detector array to detect neutrons along with light charged particles. In a reaction induced by stable and exotic heavy-ions beams, where copious production of neutrons and other light charged particles occurs, discrimination with low identification threshold of these particles are of great importance. In view of this, EJ 299-33 scintillator having dimension of 3 cm × 3 cm × 3 cm backed by a photomultiplier tube was tested and used under vacuum to detect neutrons, gamma-rays and alpha particles emitted by radioactive sources. Anode pulses from the photomultiplier tube were digitized through GET electronics, recorded and stored in a data acquisition system for the purpose of an off-line analysis. The measurements, under vacuum and low background conditions, show good pulse shape discrimination properties characterized by low identification threshold for neutrons, gamma-rays and alpha particles. The Figures of Merit for neutron-gamma and alpha particles-gamma discriminations have been evaluated together with the energy resolution for gamma-ray and alpha particles.

In this paper we briefly discuss about a novel application of the IMF- IMF correlation function in the physics case of heavy projectile-like (PLF) binary fission-like massive splitting in heavy ion collisions at Fermi energy. In particular, results are shown for the reverse kinematics reaction 124Sn+64Ni at 35 AMeV that has been investigated by using the forward part of CHIMERA multi-detector. Transport CoMD simulations are compared with the data. The main analysis was performed as a function of the charge asymmetry of the decay channel. The coexistence of dynamical and statistical components as a function of the charge asymmetry of the binary breakup is clearly evidenced. We show that the IMF-IMF correlation functions, when coupled with transport calculations, can be used to pin down the timescale of the fragments production and consequently the relevant ingredients of the in medium effective interaction. Efforts are being planned to extend the method to different reaction mechanisms and nuclear systems and, also, to compare the data with different transport theory simulations.

International audience; At Laboratori Nazionali del Sud of Catania an experiment has been carried out in order to investigate the correlations between particles produced in 12C+24Mg reaction at 35 AMeV incident energy. Two α correlation has been explored because provide information about temperature of 8Be nuclei produced in the reaction, while three α correaltion has been studied in order to evaluate the competition between sequential and direct decay mode of resonances produced in 12C quasi-projectiles.

International audience; In heavy-ion collisions at low energy, the decay mode of the compound nucleus formed in fusion reactions can be strongly influenced by the isospin degree of freedom, strictly connected to the isotopic ratio N/Z of the system. The competition among the disintegration modes of 118,134Ba∗ produced in 78,86Kr+40,48Ca reactions at 10 A MeV has been studied in the framework of the ISODEC experiment, and experimental data have been compared with the prediction of GEMINI++ and DiNuclear System (DNS) models.

In view of the first application in the framework of the FARCOS project, we designed a compact 6U board that provides in a single module 256 channels featuring: i) differential to single-ended low-noise conversion with $100 \Omega $ input impedance, ii) a second order or a fourth order anti-aliasing filter, iii) a selectable output offset voltage. The first stage is responsible of the conversion from the differential mode to single-ended and features an additional input for offset regulation. The second stage is the filtering stage, designed as a Sallen-Key cell with cutoff frequency of 40 MHz. The design relies on very small case dual operational amplifiers and clusters 4 channels in a common design sharing the offset regulation section. The 4-channel cluster occupies an area of 3.5 mm $\times 110$ mm. The paper illustrates the designed module topology and the results of the characterization of a 4-channel cluster.

Few years ago we proposed a novel detection system textbf- named FARCOS (Femtoscopy ARray for COrrelations andSpectroscopy) – to target different open cases in nuclear physics. The basic cluster unit of the FARCOS array is a telescope structure with an active area of $6.4 \times 6.4$ cm$^{\mathbf {2}}$ composed of three detection stages. The first two detection layers are DC-coupled Double-Sided Silicon Strip Detectors (DSSSDs), 300 $\mu \textbf{m}$ thick and 1500 $\mu \textbf{m}$ thick, featuring $32 \times 32$ orthogonal strips. The third stage, acting as calorimeter, is composed of four truncated pyramids of CsI(Tl) crystals with an active area of $3.2 \times 3.2$ cm$^{\mathbf {2\, }}$textbfand an absorption length of 6 cm arranged in window configuration. The final system will be a modular assembly of 20 telescopes.A key feature of FARCOS is the identification of the particles stopping even in the first detection layer, relying on pulse shape analysis techniques. The FARCOS frontend electronics features a full scale energy range up to 2 GeV with 5 different selectable ranges and an energy resolution down to 10 keV FWHM with a power budget of about 10 mW/channel in the case of the lower full scale energy range. Its core is a custom multichannel charge preamplifier VLSI chip.The system performance has been extensively qualified on few workhorses in view of the assembly of the final telescopes foreseen for 2018.

In order to upgrade the performance of the frontend of the silicon layers of the FARCOS telescopes especially in terms of the available full-scale energy range (up to 2 GeV) to study the Pigmy Dipole Resonance in $^{68}$ Ni nuclei (i.e. with an isoscalar probe) we developed a CMOS frontend in C35B4C3 AMS technology for the readout of the Double Sided Silicon Strip Detectors of the FARCOS telescopes. The preamplifier features a continuous-reset feedback and an input PMOS transistor in telescopic cascode configuration. In this work we present the design of the charge preamplifier and the results of the experimental qualification of a prototype version of the circuit.

We present a new method for the measurement of very small Γ γ partial width that is important for the synthesis of elements in astrophysics. The method is based on the simultaneous detection of scattered beam, residual nucleus and decay γ rays. This method is optimized for the use of the CHIMERA detector at LNS. Experimental details are described.

International audience; In the ASY-EOS experiment flows of neutrons and light charged particles were measured for (197)Au+(197)Au collisions at 400 MeV/nucleon, in order to investigate the strength of the symmetry term of the nuclear equation of state at supra-saturation densities. By comparing the experimental data with the UrQMD transport model predictions, we have extracted a new constraint in agreement with the moderately soft to linear density dependence obtained in the former analysis on FOPI-LAND data, but reducing the associated uncertainty by a factor ∼ 2.

International audience; The possible existence of cluster structures in 16C has been investigated by inspecting their breakup (induced on CH2 targets) in 10Be+6He events. The excitation energy of the projectile nucleus prior to decay is obtained via an invariant mass analysis of identified fragments. The experiment has been carried out at the FRIBs facility of INFN-LNS, by using a fragmentation cocktail beam at intermediate energies (≈ 55 MeV/nucleon) and the CHIMERA 4π multi-detector. A non-vanishing yield in the 10Be+6He correlations is reported at an excitation energy of about 20.5 MeV in 16C, in analogy with previous works. To improve these results, we recently performed a new experiment by coupling CHIMERA and FARCOS at forward angles. Preliminary details of the new experiment are reported in the text.

International audience; A comprehensive study of the evolution of the GDR properties from E∗ = 150 MeV to E∗ = 430 MeV has been undertaken in nuclei of mass A = 120 ÷ 132. The experimental investigation was performed using MEDEA detector. An onset of a quenching of the GDR gamma yield was found at E∗ = 270 MeV comparing the experimental gamma-ray spectrum with statistical model calculation. The quenching effect increases at E∗ = 330 MeV and is even more pronounced when the analysis is extended to higher excitation energies using data from previously performed experiments. The comparison with phenomenological models describing the quenching phenomenon gives a qualitative explanation for the effect but is not able to reproduce its detailed features as a function of excitation energy. A smooth cut-off approach describes reasonably well the progressive disappearance of the dipole strength, which occurs around 220–230 MeV excitation energy, and shows that the GDR quenching is a rather sharp effect.