Multi-breakup processes for the 124 Sn+ 64 Ni system at 35 MeV/nucleon have been studied with the... more Multi-breakup processes for the 124 Sn+ 64 Ni system at 35 MeV/nucleon have been studied with the forward part of the CHIMERA detector. An extensive comparison between experimental data corresponding to almost complete ternary events and constrained molecular dynamics (CoMD-II) calculations suggests different characteristic times in the selected processes. This is in agreement with previous studies of the same reaction already published concerning the prompt intermediate-mass-fragment emission. Stimulated by CoMD-II calculations, we investigate the existence of more complex dynamical multi-breakup processes occurring on the same time scale. A detailed study of the rotational dynamics leading to slower dynamical fission processes is also presented.
It is shown how many-body correlations involving the symmetry potential naturally arise in the mo... more It is shown how many-body correlations involving the symmetry potential naturally arise in the molecular dynamics CoMD-II model. The effect of these correlations on the collision dynamics at the Fermi energies is discussed. Small level of correlations for systems of moderate asymmetry are able to produce large effects also in simple observables like the charge distributions. The comparison with predictions based on EOS static calculations is also discussed.
We present a new experimental method to correlate the isotopic composition of intermediate mass f... more We present a new experimental method to correlate the isotopic composition of intermediate mass fragments (IMF) emitted at mid-rapidity in semi-peripheral collisions with the emission timescale: IMFs emitted in the early stage of the reaction show larger values of <N/Z> isospin asymmetry, stronger angular anisotropies and reduced odd-even staggering effects in neutron to proton ratio <N/Z> distributions than those produced in sequential statistical emission. All these effects support the concept of isospin "migration", that is sensitive to the density gradient between participant and quasi-spectator nuclear matter, in the so called neck fragmentation mechanism. By comparing the data to a Stochastic Mean Field (SMF) simulation we show that this method gives valuable constraints on the symmetry energy term of nuclear equation of state at subsaturation densities. An indication emerges for a linear density dependence of the symmetry energy.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1998
As a result of a collaboration between SGS-Thomson and INFN, a Monolithic Silicon Detector Telesc... more As a result of a collaboration between SGS-Thomson and INFN, a Monolithic Silicon Detector Telescope with ΔE/E of 4×4mm2 with an ultra-thin ΔE stage (1μm) has been recently presented as a tool to identify low-energy heavy ions. The good performances obtained in the charge identification are anyway limited by the relatively small active area. We report on two new larger
Mass and atomic-number identification (ID) of reaction products is a fundamental requirement of a... more Mass and atomic-number identification (ID) of reaction products is a fundamental requirement of any nuclear reaction study. An effective particle-ID method is demonstrated, based on pulse shape analysis/discrimination (PSD) applied to large-area, single-element silicon detectors. This technique uses commercial electronic modules and achieves atomic number resolution rivaling that typically obtained with multi-element (ΔE-E) detector telescopes. The method is applied to the CHIMERA detector system without compromising its time-of-flight (TOF) resolution. Inbeam tests of the PSD method have been performed with largearea, 300-μm thick CHIMERA silicon detectors, measuring particles from the 19 F + 12 C reaction at Tandem energies. Performance of a simple PSD set up is discussed, for front and rear particle injection.
Different aspects of the formation and decay of 24Mg in the collision 13N+11B have been studied u... more Different aspects of the formation and decay of 24Mg in the collision 13N+11B have been studied using a large solid angle and highly segmented Silicon strip detector. Results concerning the fusion cross section, the 6 alpha decay of 24Mg and the GDR gamma ray emission are discussed.
Intermediate energy beams of light exotic nuclei have been produced at LNS by the FRIBs facility.... more Intermediate energy beams of light exotic nuclei have been produced at LNS by the FRIBs facility. Thanks to these beams, a complex study of the structure of halo nuclei in the 11 Be region has been started exploiting the performances of the CHIMERA array.
2000 IEEE Nuclear Science Symposium. Conference Record (Cat. No.00CH37149)
In nuclear physics at intermediate energies the use of multidetector arrays consisting of thousan... more In nuclear physics at intermediate energies the use of multidetector arrays consisting of thousands of detectors is customary. For each event up to one hundred of detection cells are hit. As usual in the case of a large number of detectors tools are needed for their stability control and the data analysis automation. This paper presents a simple, novel approach
Decay modes of excited compound systems 118 Ba and 134 Ba, produced respectively in the 78 Kr+ 40... more Decay modes of excited compound systems 118 Ba and 134 Ba, produced respectively in the 78 Kr+ 40 Ca and 86 Kr+ 48 Ca collisions at 10 A•MeV, are investigated. In particular, the competition between the various disintegration path of medium mass compound nuclei, formed by fusion processes, the production of the so referred Intermediate Mass Fragments (IMF), and the isospin dependence of the decay process are studied. Data were taken at the INFN-Laboratori Nazionali del Sud (LNS) by using the CHIMERA array. Data analysis is in progress; a first indication on the average-energy angular distributions suggests pre-equilibrium effects affecting the data and the presence of isotopical effects.
De-excitation modes of compound systems 118 Ba and 134 Ba, produced respectively in the 78 Kr+ 40... more De-excitation modes of compound systems 118 Ba and 134 Ba, produced respectively in the 78 Kr+ 40 Ca and 86 Kr+ 48 Ca collisions at 10 A.MeV, are investigated. In particular, the competition between the various disintegration decay paths of medium mass compound nuclei, formed by fusion processes and the isospin (related to N/Z) of the entrance channel influence on the decay process, are studied. Data were taken at the INFN-Laboratori Nazionali del Sud (LNS) in ISODEC experiment, by using the CHIMERA array. The experiment complements and improves the previous experiment performed at GANIL where the same mechanisms were studied at lower excitation energies. The results show the presence of a relaxed component in the reaction mechanism, evident staggering effects in the Z distributions, as well as different isotopic composition and neutron enrichment for the reaction products in the two systems.
The energy spectra of the γ-rays emitted in the 35 Cl + 92 Mo reaction at incident energy E = 260... more The energy spectra of the γ-rays emitted in the 35 Cl + 92 Mo reaction at incident energy E = 260 MeV were measured in coincidence with the ejectiles produced in dissipative reaction events. The cumulative energy spectrum of the γ-rays coming from the decay of the ejectiles was calculated within the statistical model and its comparison to the experimental spectrum evidences an excess in the data for E γ = 8 to 12 MeV. Such an excess, fitted with a Lorentz curve, is attributed to the preequilibrium GDR γ-decay of the intermediate dinuclear system. The centroid energy of the Lorentz curve corresponds to a dipole oscillation along the symmetry axis of the system and its width is found to be comparable to that of the ground state GDR low energy component of the deformed dinucleus. The small quantal dispersion ∆ = (10.3 ± 0.1)~of the entrance channel angular momentum, determined by analysing the dissipative fragment angular distribution in the framework of the Strutinsky model, is suggested to limit the broadening of the preequilibrium GDR width.
We discuss experimental data concerning 48 Ca+ 48 Ca and 42 Ca+ 54 Fe reactions at 25 MeV/nucleon... more We discuss experimental data concerning 48 Ca+ 48 Ca and 42 Ca+ 54 Fe reactions at 25 MeV/nucleon obtained by using the 4 multi-detector Chimera. Effects due due to the different neutron to proton ratios (N/Z) of the two systems have been investigated. Charge distributions of forwardly emitted fragments show even-odd staggering whose amplitude is larger for the neutron poor system. Moreover, the neutron excess of the total system influence the evolution of fusion-like sources formed in semi-central collisions. In particular, for the neutron rich system, the relative emission yield of heavy residues is larger, while multi-fragmentation and binary-like events prevail in the neutron poor system.
New Projects and Lines of Research in Nuclear Physics, 2003
We present the characteristics of a new multidetector based on monolithic silicon telescopes. In ... more We present the characteristics of a new multidetector based on monolithic silicon telescopes. In such telescopes the DeltaE and residual energy stages are integrated on a single silicon chip and extremely thin DeltaE stages can be obtained.
Fusion and direct processes have been studied for the 6He + 64Zn reaction at energies around the ... more Fusion and direct processes have been studied for the 6He + 64Zn reaction at energies around the Coulomb barrier, in order to investigate the effects of the projectile halo structure on the reaction mechanisms. As comparison, the 4He + 64Zn reaction was also studied. No effect has been observed on the fusion cross section for the 6He when compared with
Nucleus-Nucleus Collisions - Proceedings of the Conference Bologna 2000: Structure of the Nucleus at the Dawn of the Century, 2001
gamma-rays in coincidence with heavy evaporation residues have been measured for the reactions 40... more gamma-rays in coincidence with heavy evaporation residues have been measured for the reactions 40Ca+48,40Ca, 46Ti at 25A MeV beam energy. A large enhancement in the gamma-ray multiplicity has been found in the 40Ca+48Ca data with respect to the 40Ca+40Ca ones. Different contributions to this enhancement have been identified. One of these contributions is centred, in the spectra ratio, around Egamma=10
The reaction 6He+64Zn was studied in order to investigate the effects of the halo structure on th... more The reaction 6He+64Zn was studied in order to investigate the effects of the halo structure on the fusion cross-section at low bombarding energy. The evaporation residues were identified by measuring off-line the X-ray emission which follows their Electron Capture decay. The reaction 4He+64Zn was also measured and the results are presented.
The authors present the construction and first test results of a DeltaE-E telescope for Z-identif... more The authors present the construction and first test results of a DeltaE-E telescope for Z-identification.
We discuss two experimental techniques we are using to study fusion reactions, above and below th... more We discuss two experimental techniques we are using to study fusion reactions, above and below the barrier, induced by weakly bound radioactive nuclei. In order to study fusion reactions induced by the halo nucleus 6He on 64Zn around and below the barrier, we detect off-line atomic X-rays following the electron capture decay of the evaporation residues. To investigate on the
Multi-breakup processes for the 124 Sn+ 64 Ni system at 35 MeV/nucleon have been studied with the... more Multi-breakup processes for the 124 Sn+ 64 Ni system at 35 MeV/nucleon have been studied with the forward part of the CHIMERA detector. An extensive comparison between experimental data corresponding to almost complete ternary events and constrained molecular dynamics (CoMD-II) calculations suggests different characteristic times in the selected processes. This is in agreement with previous studies of the same reaction already published concerning the prompt intermediate-mass-fragment emission. Stimulated by CoMD-II calculations, we investigate the existence of more complex dynamical multi-breakup processes occurring on the same time scale. A detailed study of the rotational dynamics leading to slower dynamical fission processes is also presented.
It is shown how many-body correlations involving the symmetry potential naturally arise in the mo... more It is shown how many-body correlations involving the symmetry potential naturally arise in the molecular dynamics CoMD-II model. The effect of these correlations on the collision dynamics at the Fermi energies is discussed. Small level of correlations for systems of moderate asymmetry are able to produce large effects also in simple observables like the charge distributions. The comparison with predictions based on EOS static calculations is also discussed.
We present a new experimental method to correlate the isotopic composition of intermediate mass f... more We present a new experimental method to correlate the isotopic composition of intermediate mass fragments (IMF) emitted at mid-rapidity in semi-peripheral collisions with the emission timescale: IMFs emitted in the early stage of the reaction show larger values of <N/Z> isospin asymmetry, stronger angular anisotropies and reduced odd-even staggering effects in neutron to proton ratio <N/Z> distributions than those produced in sequential statistical emission. All these effects support the concept of isospin "migration", that is sensitive to the density gradient between participant and quasi-spectator nuclear matter, in the so called neck fragmentation mechanism. By comparing the data to a Stochastic Mean Field (SMF) simulation we show that this method gives valuable constraints on the symmetry energy term of nuclear equation of state at subsaturation densities. An indication emerges for a linear density dependence of the symmetry energy.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1998
As a result of a collaboration between SGS-Thomson and INFN, a Monolithic Silicon Detector Telesc... more As a result of a collaboration between SGS-Thomson and INFN, a Monolithic Silicon Detector Telescope with ΔE/E of 4×4mm2 with an ultra-thin ΔE stage (1μm) has been recently presented as a tool to identify low-energy heavy ions. The good performances obtained in the charge identification are anyway limited by the relatively small active area. We report on two new larger
Mass and atomic-number identification (ID) of reaction products is a fundamental requirement of a... more Mass and atomic-number identification (ID) of reaction products is a fundamental requirement of any nuclear reaction study. An effective particle-ID method is demonstrated, based on pulse shape analysis/discrimination (PSD) applied to large-area, single-element silicon detectors. This technique uses commercial electronic modules and achieves atomic number resolution rivaling that typically obtained with multi-element (ΔE-E) detector telescopes. The method is applied to the CHIMERA detector system without compromising its time-of-flight (TOF) resolution. Inbeam tests of the PSD method have been performed with largearea, 300-μm thick CHIMERA silicon detectors, measuring particles from the 19 F + 12 C reaction at Tandem energies. Performance of a simple PSD set up is discussed, for front and rear particle injection.
Different aspects of the formation and decay of 24Mg in the collision 13N+11B have been studied u... more Different aspects of the formation and decay of 24Mg in the collision 13N+11B have been studied using a large solid angle and highly segmented Silicon strip detector. Results concerning the fusion cross section, the 6 alpha decay of 24Mg and the GDR gamma ray emission are discussed.
Intermediate energy beams of light exotic nuclei have been produced at LNS by the FRIBs facility.... more Intermediate energy beams of light exotic nuclei have been produced at LNS by the FRIBs facility. Thanks to these beams, a complex study of the structure of halo nuclei in the 11 Be region has been started exploiting the performances of the CHIMERA array.
2000 IEEE Nuclear Science Symposium. Conference Record (Cat. No.00CH37149)
In nuclear physics at intermediate energies the use of multidetector arrays consisting of thousan... more In nuclear physics at intermediate energies the use of multidetector arrays consisting of thousands of detectors is customary. For each event up to one hundred of detection cells are hit. As usual in the case of a large number of detectors tools are needed for their stability control and the data analysis automation. This paper presents a simple, novel approach
Decay modes of excited compound systems 118 Ba and 134 Ba, produced respectively in the 78 Kr+ 40... more Decay modes of excited compound systems 118 Ba and 134 Ba, produced respectively in the 78 Kr+ 40 Ca and 86 Kr+ 48 Ca collisions at 10 A•MeV, are investigated. In particular, the competition between the various disintegration path of medium mass compound nuclei, formed by fusion processes, the production of the so referred Intermediate Mass Fragments (IMF), and the isospin dependence of the decay process are studied. Data were taken at the INFN-Laboratori Nazionali del Sud (LNS) by using the CHIMERA array. Data analysis is in progress; a first indication on the average-energy angular distributions suggests pre-equilibrium effects affecting the data and the presence of isotopical effects.
De-excitation modes of compound systems 118 Ba and 134 Ba, produced respectively in the 78 Kr+ 40... more De-excitation modes of compound systems 118 Ba and 134 Ba, produced respectively in the 78 Kr+ 40 Ca and 86 Kr+ 48 Ca collisions at 10 A.MeV, are investigated. In particular, the competition between the various disintegration decay paths of medium mass compound nuclei, formed by fusion processes and the isospin (related to N/Z) of the entrance channel influence on the decay process, are studied. Data were taken at the INFN-Laboratori Nazionali del Sud (LNS) in ISODEC experiment, by using the CHIMERA array. The experiment complements and improves the previous experiment performed at GANIL where the same mechanisms were studied at lower excitation energies. The results show the presence of a relaxed component in the reaction mechanism, evident staggering effects in the Z distributions, as well as different isotopic composition and neutron enrichment for the reaction products in the two systems.
The energy spectra of the γ-rays emitted in the 35 Cl + 92 Mo reaction at incident energy E = 260... more The energy spectra of the γ-rays emitted in the 35 Cl + 92 Mo reaction at incident energy E = 260 MeV were measured in coincidence with the ejectiles produced in dissipative reaction events. The cumulative energy spectrum of the γ-rays coming from the decay of the ejectiles was calculated within the statistical model and its comparison to the experimental spectrum evidences an excess in the data for E γ = 8 to 12 MeV. Such an excess, fitted with a Lorentz curve, is attributed to the preequilibrium GDR γ-decay of the intermediate dinuclear system. The centroid energy of the Lorentz curve corresponds to a dipole oscillation along the symmetry axis of the system and its width is found to be comparable to that of the ground state GDR low energy component of the deformed dinucleus. The small quantal dispersion ∆ = (10.3 ± 0.1)~of the entrance channel angular momentum, determined by analysing the dissipative fragment angular distribution in the framework of the Strutinsky model, is suggested to limit the broadening of the preequilibrium GDR width.
We discuss experimental data concerning 48 Ca+ 48 Ca and 42 Ca+ 54 Fe reactions at 25 MeV/nucleon... more We discuss experimental data concerning 48 Ca+ 48 Ca and 42 Ca+ 54 Fe reactions at 25 MeV/nucleon obtained by using the 4 multi-detector Chimera. Effects due due to the different neutron to proton ratios (N/Z) of the two systems have been investigated. Charge distributions of forwardly emitted fragments show even-odd staggering whose amplitude is larger for the neutron poor system. Moreover, the neutron excess of the total system influence the evolution of fusion-like sources formed in semi-central collisions. In particular, for the neutron rich system, the relative emission yield of heavy residues is larger, while multi-fragmentation and binary-like events prevail in the neutron poor system.
New Projects and Lines of Research in Nuclear Physics, 2003
We present the characteristics of a new multidetector based on monolithic silicon telescopes. In ... more We present the characteristics of a new multidetector based on monolithic silicon telescopes. In such telescopes the DeltaE and residual energy stages are integrated on a single silicon chip and extremely thin DeltaE stages can be obtained.
Fusion and direct processes have been studied for the 6He + 64Zn reaction at energies around the ... more Fusion and direct processes have been studied for the 6He + 64Zn reaction at energies around the Coulomb barrier, in order to investigate the effects of the projectile halo structure on the reaction mechanisms. As comparison, the 4He + 64Zn reaction was also studied. No effect has been observed on the fusion cross section for the 6He when compared with
Nucleus-Nucleus Collisions - Proceedings of the Conference Bologna 2000: Structure of the Nucleus at the Dawn of the Century, 2001
gamma-rays in coincidence with heavy evaporation residues have been measured for the reactions 40... more gamma-rays in coincidence with heavy evaporation residues have been measured for the reactions 40Ca+48,40Ca, 46Ti at 25A MeV beam energy. A large enhancement in the gamma-ray multiplicity has been found in the 40Ca+48Ca data with respect to the 40Ca+40Ca ones. Different contributions to this enhancement have been identified. One of these contributions is centred, in the spectra ratio, around Egamma=10
The reaction 6He+64Zn was studied in order to investigate the effects of the halo structure on th... more The reaction 6He+64Zn was studied in order to investigate the effects of the halo structure on the fusion cross-section at low bombarding energy. The evaporation residues were identified by measuring off-line the X-ray emission which follows their Electron Capture decay. The reaction 4He+64Zn was also measured and the results are presented.
The authors present the construction and first test results of a DeltaE-E telescope for Z-identif... more The authors present the construction and first test results of a DeltaE-E telescope for Z-identification.
We discuss two experimental techniques we are using to study fusion reactions, above and below th... more We discuss two experimental techniques we are using to study fusion reactions, above and below the barrier, induced by weakly bound radioactive nuclei. In order to study fusion reactions induced by the halo nucleus 6He on 64Zn around and below the barrier, we detect off-line atomic X-rays following the electron capture decay of the evaporation residues. To investigate on the
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