A new type of spallation experiments has been carried out at GSI, Darmstadt (Germany) in order to understand the spallation mechanism in greater details. These experiments use the inverse-kinematics technique where the ion beam is directed onto a liquid Hydrogen target, allowing the detection of heavy spallation residues in coincidence with low center-of-mass energy light particles. The setup is based on A Large Acceptance DIpole magNet (ALADIN) coupled with a multitrack Time Projection Chamber (TPC), a hodoscope and a neutron detector. First data on Fe+p at 1 A GeV were taken in February, 04. In the on-going analysis, isotopic cross sections have been determined and compared to data taken at the FRagment Separator in GSI. Mean values and width of residue velocity distributions have also been obtained as well as Helium production cross section. First coincidence data are being analyzed.

Isotopic production cross sections of residual nuclei in the spallation reaction Xe (200A MeV) + p C. Paradela,1,2,* L. Tassan-Got,1 J. Benlliure,2 J. L. Rodríguez-Sánchez,2 L. Audouin,1 A. Boudard,3 E. Casarejos,2,† T. Enqvist,4 J. E. Ducret,3 F. Farget,1,‡ B. Fernández-Domínguez,3,§ M. Fernández Ordóñez,2 L. Giot,4,‖ A. Heinz,4,¶ V. Henzl,4 D. Henzlova,4 A. Kelić-Heil,4 A. Lafriaskh,1 S. Leray,3 P. Napolitani,1 J. Pereira,2,# D. Pérez-Loureiro,2,# M. V. Ricciardi,4 C. Stéphan,1 K.-H. Schmidt,4 C. Schmitt,4,‡ C. Villagrasa,3 C. Volant,3 and O. Yordanov4,** 1IPN, CNRS/IN2P3, Université Paris-Sud 11, F-91406 Orsay, France 2Universidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain 3IRFU, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France 4GSI-Helmholtzzentrum für Schwerionenforschung GmbH, D-64291 Darmstadt, Germany (Received 31 January 2017; published 10 April 2017)

The residual nuclei produced in the spallation reaction of Xe-136 nuclei at 200A MeV on protons have been studied by measuring the isotopic distributions for the elements from cadmium (Z = 48) to cesium (Z = 55) by using the fragment separator (FRS) spectrometer at GSI and the inverse kinematics technique. This is one of the few measurements performed at such a low projectile energy, close to the validity limit for intranuclear cascade models such as INCL or ISABEL. The experimental results have been compared to these intranuclear cascade codes coupled to the evaporation code ABLA. Both code combinations reproduce qualitatively the measured isotopic distributions; however, both underestimate the production of residues with mass numbers between 126 and 134. The measured cross sections are of interest for the planning of future radioactive beam or neutron source facilities.

Residual fragment production in reactions induced by Xe-136 projectiles impinging on a liquid deuterium target at 500A MeV has been measured at GSI. Projectile residues were unambiguously identified in atomic and mass numbers using the Fragment Separator as high-resolution zero-degree spectrometer. The isotopic production yields of these residuals were used to benchmark reference model calculations describing spallation reactions. In particular the energy dissipated in these reactions was assessed by comparing the production yields measured in this work with the ones obtained in reactions induced by 136Xe projectiles on protons at 1000A and 500A MeV.

Residual fragment production in reactions induced by Xe136 projectiles impinging on a liquid deuterium target at 500A MeV has been measured at GSI. Projectile residues were unambiguously identified in atomic and mass numbers using the Fragment Separator as high-resolution zero-degree spectrometer. The isotopic production yields of these residuals were used to benchmark reference model calculations describing spallation reactions. In particular the energy dissipated in these reactions was assessed by comparing the production yields measured in this work with the ones obtained in reactions induced by Xe136 projectiles on protons at 1000A and 500A MeV.5 MoreReceived 27 May 2015DOI:https://doi.org/10.1103/PhysRevC.92.024607©2015 American Physical Society

Around 270 medium-mass residual nuclei, formed in spallation reactions induced by Xe-136 projectiles impinging on a liquid hydrogen target at 500 A MeV, have been unambiguously identified at GSI using the magnetic spectrometer FRS. The individual production cross sections and the longitudinal momentum distributions have been determined with high accuracy. These data represent an important constraint for theoretical models describing spallation reactions. (C) 2013 Elsevier B.V. All rights reserved.

The performance of the LAND neutron detector is studied. Using an event-mixing technique based on one-neutron data obtained in the S107 experiment at the GSI laboratory, we test the efficiency of various analytic tools used to determine the multiplicity and kinematic properties of detected neutrons. A new algorithm developed recently for recognizing neutron showers from spectator decays in the ALADIN experiment S254 is described in detail. Its performance is assessed in comparison with other methods. The properties of the observed neutron events are used to estimate the detection efficiency of LAND in this experiment.

Received 19 December 2011DOI:https://doi.org/10.1103/PhysRevC.85.019903©2012 American Physical Society

The slowing down of fast electrons emitted from insulators [Mylar, polypropylene (PP)] irradiated with swift ion beams (C, O, Kr, Ag, Xe; 20-64 MeV/u) was measured by the time-of-flight method at LNS, Catania and GANIL, Caen. The charge buildup, deduced from both convoy- and binary-encounter electron peak shifts, leads to target material-dependent potentials (6.0 kV for Mylar, 2.8 kV for PP). The number of projectiles needed for charging up (charging-up time constant) is inversely proportional to the electronic energy loss. After a certain time, a sudden decharging occurs. For low beam currents, charging-up time, energy shift corresponding to maximum charge buildup, and time of decharging are regular. For high beam currents, the time intervals become irregular (chaotic).

The N/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at the GSI Schwerionen Synchrotron (SIS). Stable and radioactive Sn and La beams with an incident energy of 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. For the interpretation of the data, calculations with the statistical multifragmentation model for a properly chosen ensemble of excited sources were performed. The parameters of the ensemble, representing the variety of excited spectator nuclei expected in a participant-spectator scenario, are determined empirically by searching for an optimum reproduction of the measured fragment-charge distributions and correlations. An overall very good agreement is obtained. The possible modification of the liquid-drop parameters of the fragment description in the hot freeze-out environment is studied, and a significant reduction of the symmetry-term coefficient is found necessary to reproduce the mean neutron-to-proton ratios /Z and the isoscaling parameters of Z<=10 fragments. The calculations are, furthermore, used to address open questions regarding the modification of the surface-term coefficient at freeze-out, the N/Z dependence of the nuclear caloric curve, and the isotopic evolution of the spectator system between its formation during the initial cascade stage of the reaction and its subsequent breakup.

A phase transition signature associated with cumulants of the largest fragment size distribution has been identified in statistical multifragmentation models and examined in analysis of the ALADIN S254 data on fragmentation of neutron-poor and neutron-rich projectiles. Characteristics of the transition point indicated by this signature are weakly dependent on the A/Z ratio of the fragmenting spectator source. In particular, chemical freeze-out temperatures are estimated within the range 5.9 to 6.5 MeV. The experimental results are well reproduced by the SMM model.

The interaction of ion beams with insulators leads to charging-up phenomena, which at present are under investigation in connection with guiding phenomena in nanocapillaries with possible application in nanofocused beams. We studied the charging dynamics of insulating foil targets [Mylar, polypropylene (PP)] irradiated with swift ion beams (C, O, Ag, and Xe at 40, 23, 40, and 30 MeV/u, respectively) via the measurement of the slowing down of fast binary-encounter electrons. Also, sandwich targets (Mylar covered with a thin Au layer on both surfaces) and Mylar with Au on only one surface were used. Fast-electron spectra were measured by the time-of-flight method at the superconducting cyclotron of Laboratori Nazionali del Sud (LNS) Catania. The charge buildup leads to target-material-dependent potentials of the order of 6.0 kV for Mylar and 2.8 kV for PP. The sandwich targets, surprisingly, show the same behavior as the insulating targets, whereas a single Au layer on the electron and ion exit side strongly suppresses the charging phenomenon. The accumulated number of projectiles needed for charging up is inversely proportional to electronic energy loss. Thus, the charging up is directly related to emission of secondary electrons.

More than 600 residual nuclei, formed in the spallation of 136Xe projectiles impinging on deuterium at 500 AMeV of incident energy, have been unambiguously identified and their production cross sections have been determined with high accuracy. By comparing these data to others previously measured for the reactions 136Xe + p at 1 AGeV and 136Xe + p at 500 AMeV we investigated the role that neutrons play in peripheral collisions and to understand the energy dissipation in frontal collisions in spallation reactions.

Isospin diffusion is probed as a function of the dissipated energy by studying two systems 58Ni+58Ni and 58Ni+197Au, over the incident energy range 52-74A MeV. Experimental data are compared with the results of a microscopic transport model with two different parameterizations of the symmetry energy term. A better overall agreement between data and simulations is obtained when using a symmetry term with a potential part linearly increasing with nuclear density. The isospin equilibration time at 52 A MeV is estimated to 130 ± 10 fm/c.

More than six hundred nuclei produced in the fragmentation of Xe-136 projectiles at 500 A MeV on a liquid deuterium target were identified using inverse kinematics at the GSI Fragment Separator (FRS). These data are relevant for understanding of spallation reactions.

Isospin diffusion in semiperipheral collisions is probed as a function of the dissipated energy by studying two systems Ni-58+Ni-58 and Ni-58+Au-197, over the incident energy range 52A-74A MeV. A close examination of the multiplicities of light products in the forward part of the phase space clearly shows an influence of the isospin of the target on the neutron richness of these products. A progressive isospin diffusion is observed when collisions become more central, in connection with the interaction time..

The A/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of (124)Sn and radioactive beams of (124)La and (107)Sn at 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z of the produced spectator sources, consistent with predictions for expanded systems. Small Coulomb effects (DeltaT approximately 0.6 MeV) appear for residue production near the onset of multifragmentation.

Production cross sections of medium-mass neutron-rich nuclei obtained in the fragmentation of Xe-136 projectiles at 1 A GeV have been measured with the FRagment Separator (FRS) at GSI. The measured cross sections are compared to U-238 fission yields and model calculations to determine the optimum reaction mechanism to extend the limits of the chart of the nuclides around the r-process waiting point at N=82.

A research program on spallation reactions in inverse kinematics has been performed at GSI, Darmstadt, taking advantage of the relativistic heavy-ions beams available from GSI accelerators and the high-resolution magnetic spectrometer, used to identify the reactions products in-flight and to determine their kinematical properties.In this paper, we report the results obtained up to now on the spallation reaction 136 Xe on protons, focusing on 500 and 200 AMeV energies.