Search

The breakup of 9Be is studied via an inelastic scattering experiment on a proton target at 5.6 A MeV in inverse kinematics. Two of the three cluster constituents (α and α) as well as the proton target recoil were recorded in a triple coincidence mode allowing a full kinematics approach analysis. In this respect relative α - α and α - n, Q-value and 9Be excitation spectra, energy spectra for all fragments as well as the energy spectrum of the recoil proton were reconstructed. A clear signature of the two breakup sequential modes (5He + 4He and 8Be + n) was identified via the recoiling proton reconstructed spectra together with the direct breakup decay. A strong 5He + 4He mode was observed compatible with previous beta decay experiments.

The so-called Hoyle state in 12C (7.654 MeV, 0+) is an excited state of 12C characterized by a well-pronounced 3α cluster nature. Many possible cluster configurations, such as a linear-chain arrangement of 3α particles, bentarm, triangular or gas-like structures were theoretically conjectured within the previous decades, but, also due to the existence of ambiguities in experimental data, it is still impossible to draw a firm conclusion. Its direct α-decay partial width is accurately predicted by models but requires better experimental constraints. We performed a high-precision and high-selectivity investigation of its α-decay by using the 14N(d, α2)12C- reaction at 10.5 MeV incident energy with the aim of distinguishing between sequential and direct decay patterns. We are able to significantly improve the state of the art upper limit for direct 3α decays by placing the new limit at 0.043%. Such a low limit allows to give fundamental constraints to theoretical models attempting to describe the structure of the Hoyle state.

An intense activity in the field of experimental, as well as theoretical, nuclear structure is ongoing at the INFN-LNS laboratory in Catania. A short overview of the main recent results is reported.

Fragmentation reactions represent a serious complication in hadrontherapy and space radiation protection. In order to predict their effects, both reliable Monte Carlo codes and experimental data are needed. The shortage of precise measurements, especially of double differential cross sections, has triggered many dedicated experiments at relativistic energies. Aiming to explore the Fermi energy regime, as well, where different reaction mechanisms are involved, we measured the 12C fragmentation at 62 AMeV on a 12C and a 197Au target. A high granularity Si-CsI hodoscope allowed to identify the charge and the mass of detected fragments and measure their energy and emission angle. In this work we report the double differential cross sections for the production of different fragments as a function of the emission angle. Experimental results are compared with the GEANT-4 Monte Carlo predictions performed using two reaction models, the Quantum Molecular Dynamic and the Binary Light Ion Cascade.

International audience; The ${0}_{2}^{+}$ state in(12)C (7.654MeV, the Hoyle state) is important for the understanding of clustering phenomena in nuclei. The pronounced cluster nature of this state allows the triple-α process in stars with a reaction rate regulated by its structure properties. To precisely estimate the direct component in the 3α decay mechanism of the Hoyle state, we developed a new experiment using the(14)N(d,α)(12)C reaction at 10.5MeV. An anti-coincidence telescope was used to identify the α ejectiles leading the residual(12)C in the Hoyle state, while its decays in 3α were studied by means of a new hodoscope of silicon detectors, superOSCAR, placed in kinematical coincidence to fully reconstruct the events. Details of the experiment and preliminary results are discussed in the text.

The elastic scattering excitation function for 15O on 4He was measured - for the first time - by using the Inverse Kinematic Thick Target scattering method. The obtained spectrum was analysed in an R-matrix framework providing spectroscopic information for several states in the excitation energy of the nucleus 19Ne from 4.8 to 9 MeV. Eight of them are newly observed states. The set-up and the experimental technique will be described in detail and the results will be shown and discussed. European Unions Horizon 2020 659744

Background: For the deeply bound one-nucleon removal at intermediate energies using a $^{9}\text{Be}$ or $^{12}\text{C}$ target, a strong reduction of cross section was observed relative to the prediction of eikonal theoretical model. The large disagreement has not been explained and the systematic trend is inconsistent with results from transfer reactions. The recently observed asymmetric parallel momentum distribution of the knockout residue indicates the significant dissipative core-target interaction in the knockout reaction with a composite target, implying new reaction mechanisms beyond the eikonal reaction descriptions.Purpose: To investigate the reaction mechanism for deeply bound nucleon removal at intermediate energies.Method: Neutron removal from $^{14}\text{O}$ using a $^{12}\text{C}$ target at 60 MeV/nucleon was performed. Nucleon knockout cross sections were measured. The unbound excited states of $^{13}\text{O}$ were reconstructed by using the invariant mass method with the residues and the associated decay protons measured in coincidence. The measured cross sections are compared with an intra-nuclear cascade (INC) prediction.Results: The measured cross section of ($^{14}\text{O}$, $^{11}\text{C}$) is 60(9) mb, which is 3.5 times larger than that of ($^{14}\text{O}$, $^{13}\text{O}$) channel. This $2pn$-removal cross section is consistent with INC prediction, which is 66 mb with the main contribution being non-direct reaction processes. On the other hand, the upper limit of the cross section for one-neutron removal from $^{14}\text{O}$ followed by proton evaporation is 4.6(20) mb, integrated up to 6 MeV above the proton separation energy of $^{13}\text{O}$. The calculated total cross section for such reaction processes by the INC model is 2.5 mb, which is within the measured upper limit.Conclusions: The data provide the first constraint on the role of core excitation and evaporation processes in deeply bound nucleon removal from asymmetric nuclei. The experiment results suggest that non-direct reaction processes, which are not considered in the eikonal model, play an important role in deeply bound nucleon removal from asymmetric nuclei at intermediate energies.

The 13 C( 18 O, 16 O) 15 C reaction has been studied at 84 MeV incident energy. The ejectiles have been momentum analized by the MAGNEX spectrometer and 15 C excitation energy spectra have been obtained up to about 20 MeV. In the region above the two-neutron separation energy, a bump has been observed at 13.7 MeV. The extracted cross section angular distribution for this structure, obtained by using different models for background, displays a clear oscillating pattern, typical of resonant state of the residual nucleus.

In this contribution we will present the future activities that our collaboration will carry out at ELI-NP (Extreme Light Infrastructure Nuclear Physics), the new multi peta-watt Laser facility, currently under construction at Bucharest (Romania). The activities concerns the study of nuclear reactions in laser plasmas. In this framework we proposed the construction of a new, general-purpose experimental set-up able to detect and identify neutrons and charged particles.

The MAGNEX large-acceptance spectrometer has been commissioned with beams from the Tandem accelerator at INFN-LNS Catania. The optics were tested with elastically-scattered 7Li, 16O and 48Ti beams with various apertures mounted after the target. The momentum dispersion was verified to be in agreement with the optics calculations. A demonstration of the particle identification capabilities of the PSD start detector and the focal plane detector was given by a measurement of the 27Al(7Li,6Li)28Al transfer reaction at a mean angle of 25°. The measured charge state distribution of 48Ti ions is in agreement with predictions for a gold stripping foil. Preliminary results of the software reconstruction of incident angle and excitation energy, obtained through matrices based on a 3D-interpolation of the measured field maps, are encouraging.

The problem of the description of magnetic field for large bending magnets is addressed in relation to the requirements of modern techniques of trajectory reconstruction. The crucial question of the interpolation and extrapolation of fields known at a discrete number of points is analysed. For this purpose a realistic field model of the large dipole of the MAGNEX spectrometer, obtained with finite elements three dimensional simulations, is used. The influence of the uncertainties in the measured field to the quality of the trajectory reconstruction is treated in detail. General constraints for field measurements in terms of required resolutions, step sizes and precisions are thus extracted.

The 12C(18O,16O)14C two-neutron transfer reaction has been studied at an incident energy of 275 MeV and the ejectiles have been momentum analysed at forward angles by the MAGNEX spectrometer. The identification of the 16O ejectiles was obtained by combining a standard ΔE-E technique with the simultaneous measurement of the angle and the position at the focal plane. The 14C excitation energy spectra have been obtained and several known bound and resonant states of the residual nuclei have been identified. The results have been compared to a previous measurement of the same reaction at 84 MeV incident energy.

The knowledge of the nuclear matrix elements for the neutrinoless double beta decay is fundamental for neutrino physics. In this paper, an innovative technique to extract information on the nuclear matrix elements by measuring the cross section of a double charge exchange nuclear reaction is proposed. The basic point is that the initial and final state wave functions in the two processes are the same and the transition operators are similar. The double charge exchange cross sections can be factorized in a nuclear structure term containing the matrix elements and a nuclear reaction factor. First pioneering experimental results for the 40Ca(18O,18Ne)40Ar reaction at 270 MeV incident energy show that such cross section factorization reasonably holds for the crucial 0+ --> 0+ transition to 40Args, at least at very forward angles.

Study on clustering of nucleons in nuclei is recently focusing on unstable nuclei where new kinds of structures, namely molecular structures with excess nucleons, are predicted. The Coulomb shift of energy in the mirror system is suggested to reflect the size of these structures. Although the missing mass spectroscopy is expected to give access to these structures even beyond particle decay thresholds without any biases in excitation energy spectra but the detection of very low energy particles is challenging. To satisfy the requirement, a new active target system MAIKo has been developed at RCNP. The detector was commissioned using a 13C beam under the same kinematical condition as that of RI beam experiments.

International audience; Nuclear fragmentation processes are relevant in different fields of basic research and applied physics and are of particular interest for tumor therapy and for space radiation protection applications. The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at SIS accelerator of GSI laboratory in Darmstadt, has been designed for the measurement of different ions fragmentation cross sections at different energies between 100 and 1000 MeV/nucleon. The experiment is performed by an international collaboration made of institutions from Germany, France, Italy and Spain. The experimental apparatus is partly based on an already existing setup made of the ALADIN magnet, the MUSIC IV TPC, the LAND2 neutron detector and the TOFWALL scintillator TOF system, integrated with newly designed detectors in the interaction Region (IR) around the carbon removable target: a scintillator Start Counter, a Beam Monitor drift chamber, a silicon Vertex Detector and a Proton Tagger for detection of light fragments emitted at large angles (KENTROS). The scientific program of the FIRST experiment started on summer 2011 with the study of the 400 MeV/nucleon 12C beam fragmentation on thin (8mm) carbon target.

The main features of the MAGNEX large acceptance magnetic spectrometer are described. It has a quadrupole + dipole layout and a hybrid detector located at the focal plane. The aberrations due to the large angular (50 msr) and momentum (± 13%) acceptance are reduced by an accurate hardware design and then compensated by an innovative software ray‐reconstruction technique. The obtained resolution in energy, angle and mass are presented in the paper. MAGNEX has been used up to now for different experiments in nuclear physics and astrophysics confirming to be a multipurpose device.

A study of the 15C states was pursued in 2008 at the Catania INFN‐LNS laboratory by the 13C(18O,16O)15C reaction at 84 MeV incident energy. The 16O ejectiles were detected at forward angles by the MAGNEX magnetic spectrometer. The spectra show several known low lying states up to about 7 MeV excitation energy as well as two unknown resonant structures at about 11.4 and 13.5 MeV. The strong excitation of these latter together with the measured width of about 2 MeV FWHM could indicate the presence of collective modes of excitation connected to the transfer of a correlated neutron pair.

A technique to interpolate complex three-dimensional field distributions such as those produced by large magnets is presented. It is based on a modified charge density method where the elementary sources of the magnetic field are image charges with Gaussian shape placed on a three-dimensional surface. The strengths of the charges are found as the solution of a best-fit problem, whose special features are discussed in detail. The method is tested against the measured field of the MAGNEX large acceptance quadrupole, showing a high level of accuracy together with an effective compensation of the effect of the experimental errors present in the data. In addition the model field is in general analytical and Maxwellian. As a consequence, the reliability of the presented technique to the challenging problem of trajectory reconstruction in modern large acceptance spectrometers is demonstrated.

To investigate the spectator role of the 1g5/2 unpaired proton outside the Z = 50 closed shell, the 120Sn(p,α)117In and 121Sb(p,α)118Sn reactions have been measured in high resolution experiments at 23 MeV incident proton energy of the Munich MP Tandem accelerator, using the Stern‐Gerlach type polarized hydrogen ion source and the Q3D magnetic spectrograph.

The results of the field measurement of the large quadrupole magnet of the MAGNEX spectrometer are presented and analyzed in the view of the possible application of modern techniques of ray reconstruction. The experimental data are checked against the symmetry conditions expected for the magnet. The observed deviations are related both to imperfections on the magnet manufacturing and to the not ideal positioning of the measurement device. In particular a quantitative estimation of the experimental error in the alignment of the probe with respect to the magnet is achieved. The measured field is also compared with the results from three-dimensional finite elements calculation. The obtained discrepancies between the measured and calculated field are too large for a direct application of the latter to ray-reconstruction methods. Nevertheless, these calculations are reliably used to study the impact of the observed inaccuracies in the probe alignment on the overall precision of field reconstruction and to set quantitative constraints on the field interpolation algorithms.

A systematic study of the nuclei that can be described as an integer number of α particles plus three neutrons via the (7Li,7Be) reaction at about 8 MeV/u has shown the presence of Bound States Embedded in the Continuum in the energy spectra. These are experimental signatures of the dynamical correlations of an easily polarizable core with a single‐particle state of the valence neutron.

The MAGNEX large‐acceptance spectrometer was commissioned with beams from the LNS Tandem. First results of physical interest are presented. The obtained 10−3 energy resolution confirms the ambitious characteristic of the calculations and allows considering the instrument as an ideal tool for future studies in the field of nuclear spectroscopy and reaction mechanisms at incident energies not far form the Coulomb barrier.

We applied the digital pulse shape acquisition to the read out of the anode pads of the focal plane detector of the MAGNEX spectrometer in order to measure the position coordinates using digital signal processing.

Experimental signatures of the dynamical correlations of a core with a single-particle neutron have been found in light neutron-rich nuclei investigated via the (7Li,7Be)c harge-exchange reactions at around 8MeV/u. Of particular astrophysical relevance are low-lying narrow resonances (Γ ∼ 200 keV FWHM) BSEC (Bound States Embedded in the Continuum). Because of their long lifetime BSEC states are likely to effect the capture rates in any scenario for nucleosynthesis in neutron-rich environment. They have been observed in the continuum of 11Be and 15C nuclei. A microscopic nuclear structure model based on QRPA theory, which takes into account Dynamical Core Polarisation (DCP) correlations, gives a suitable description of these resonances as well as single-particle states of the studied systems. In this context, high-energy narrow structures populated in nuclei having an integer number of α-particles plus three neutrons are good BSEC candidates and can be systematically investigated.

The 12 C( 18 O, 16 O) 14 C reaction has been studied at 84 MeV incident energy. The ejectiles have been momentum analysed at forward angles by the MAGNEX magnetic spectrometer. The energy spectra were obtained up to about 20 MeV excitation energy. Calculations based on the removal of two uncorrelated neutrons from the projectile describe a significant part of the continuum observed in the energy spectra. In particular, a resonance of the residual nucleus dominates the region near the two-neutron emission threshold.

We present photometric and spectroscopic results on a sample of 22 northern cool stars X-ray selected by EXOSAT. Based on uvbyHβ Stromgren photometry, new spectral classifications and parallaxes for 16 cool stars were derived, from which we estimate the corresponding X-ray luminosities. Six of the 12 sources tested for light changes showed indications of variability.