arXiv subjects

A. Boudard

Publications and source records attributed to A. Boudard.

At least 19 recordsLinked to original sources

arXiv2019

Strangeness production in the new version of the Liège Intra-Nuclear Cascade model

The capabilities of the new version of the Liège Intra-Nuclear Cascade model (INCL++6) are presented in detail. This new version INCL is able to handle strange particles, such as kaons and the $Λ$ particle, and the associated reactions and also allows extending nucleon-nucleon collisions up to about $15-20$ GeV incident energy. Compared to the previous version, new observables can be studied, e.g., kaon, hyperon, and hypernuclei production cross sections (with the use of a suitable de-excitation code) as well as aspects of kaon-induced spallation reactions. The main purpose of this paper is to present the specific ingredients of the new INCL version and its new features, notably the new variance reduction scheme. We also compare for some illustrative strangeness production cases calculated using this version of INCL with experimental data.

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arXiv2018

Parametrization of cross sections for elementary hadronic collisions involving strange particles

The production of strange particles (kaons, hyperons) and hypernuclei in light charged particle induced reactions in the energy range of a few GeV (2-15 GeV) has become a topic of active research in several facilities (e.g., HypHI and PANDA at GSI and/or FAIR (Germany), JLab (USA), and JPARC (Japan)). This energy range represents the low-energy limit of the string models (degree of freedom: quark and gluon) or the high-energy limit of the so-called spallation models (degree of freedom: hadrons). A well known spallation model is INCL, the Liège intranuclear cascade model (combined with a de-excitation model to complete the reaction). INCL, known to give good results up to 2-3 GeV, was recently upgraded by the implementation of multiple pion emission to extend the energy range of applicability up to roughly 15 GeV. The next step, to account also for strange particle production, both for refining the high energy domain and making it usable when strangeness appears, requires the following main ingredients: i) the relevant elementary cross sections (production, scattering, and absorption) and ii) the characteristics of the associated final states. Some of those ingredients are already known and, sometimes, are already used in models of the same type (e.g., Bertini, GiBUU), but this paper aims at reviewing the situation by compiling, updating, and comparing the necessary elementary information which are independent of the model used.

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arXiv2018

$η$ and $ω$ mesons as new degrees of freedom in the intranuclear cascade model INCL

The intranuclear cascade model INCL (Liège Intranuclear Cascade) is now able to simulate spallation reactions induced by projectiles with energies up to roughly 15 GeV. This was made possible thanks to the implementation of multipion emission in the NN, $Δ$N and $π$N interactions. The results obtained with reactions on nuclei induced by nucleons or pions gave confidence in the model. A next step will be the addition of the strange particles, $Λ$, $Σ$ and Kaons, in order to not only refine the high-energy modeling, but also to extend the capabilities of INCL, as studying hypernucleus physics. Between those two versions of the code, the possibility to treat the $η$ and $ω$ mesons in INCL has been performed and this is the topic of this paper. Production yields of these mesons increase with energy and it is interesting to test their roles at higher energies. More specifically, studies of $η$ rare decays benefit from accurate simulations of its production. These are the two reasons for their implementation. Ingredients of the model, like elementary reaction cross sections, are discussed and comparisons with experimental data are carried out to test the reliability of those particle productions.

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arXiv2015

Excitation functions of the nat-Ta(p,x)178m2Hf and nat-W(p,x)178m2Hf reactions at energies up to 2600 MeV

Due to potential level of energy intensity 178m2Hf is an extremely interesting isomer. One possible way to produce this isomer is irradiation of nat-Ta or nat-W samples with high energy protons. Irradiation of nat-Ta and nat-W samples performed for other purposes provides an opportunity to study the corresponding reactions. This paper pre-sents the 178m2Hf independent production cross sections for both targets measured by the gamma-ray spectrometry method. The reaction excitation functions have been obtained for the proton energies from 40 up to 2600 MeV. The experimental results were compared with calculations by various versions of the intranuclear cascade model in the well-known codes: ISABEL, Bertini, INCL4.5+ABLA07, PHITS, CASCADE07 and CEM03.02. The isomer ratio for the nat-Ta(p,x)178m2Hf reaction is evaluated on the basis of the available data.

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arXiv2013

Nuclear astrophysics with radioactive ions at FAIR

The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.

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arXiv2013

Excitation Function of the nat-Ta(p,x)178m2-Hf Reaction

178m2-Hf is an extremely interesting isomeric state due to its potential energy capacity level. One possible way to obtain it is by irradiation of a nat-Ta sample with a high-current proton accelerator. Up to now, there was no information in the international experimental nuclear data base (EXFOR) for this reaction. Irradiations of nat-Ta samples performed for other purposes provide an opportunity to address this question. This paper presents the 172m2-Hf independent production cross-sections determined by gamma-ray spectrometry. The nat-Ta(p,x)172m2-Hf excitation function is studied in the 20-3500 MeV energy range. Comparisons with results by several nuclear models (ISABEL, Bertini, INCL4.5+ABLA07, PHITS, CASCADE07, and CEM03.02) used as event-generators in modern transport codes are also reported. However, since such models are generally not able to separately predict ground and isomeric states of reaction products, only 178-Hf independent and cumulative cross-section data are compared.

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arXiv2012

High-precision measurement of total fission cross sections in spallation reactions of 208Pb and 238U

Total cross sections for proton- and deuteron-induced-fission of 208Pb and 238U have been determined in the energy range between 500 MeV and 1 GeV. The experiment has been performed in inverse kinematics at GSI Darmstadt, facilitating the counting of the projectiles and the identification of the reaction products. High precision between 5 and 7 percent has been achieved by individually counting the beam particles and by registering both fission fragments in coincidence with high efficiency and full Z resolution. Fission was clearly distinguished from other reaction channels. The results were found to deviate by up to 30 percent from Prokofiev's systematics on total fission cross sections. There is good agreement with an elaborate experiment performed in direct kinematics.

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arXiv2012

Neutron recognition in the LAND detector for large neutron multiplicity

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.

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arXiv2012

Proton induced fission of 181-Ta at relativistic energies

Total fission cross sections of 181-Ta induced by protons at different relativistic energies have been measured at GSI, Darmstadt. The inverse kinematics technique used together with a dedicated set-up, made it possible to determine these cross sections with high accuracy. The new data obtained in this experiment will contribute to the understanding of the fission process at high excitation energies. The results are compared with data from previous experiments and systematics for proton-induced fission cross sections.

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arXiv2011

Verification of high-energy transport codes on the basis of activation data

Nuclide production cross sections measured at ITEP for the targets of nat-Cr, 56-Fe, nat-Ni, 93-Nb, 181-Ta, nat-W, nat-Pb, 209-Bi irradiated by protons with energies from 40 to 2600 MeV were used to estimate the predictive accuracy of several popular high-energy transport codes. A general agreement of the ITEP data with the data obtained by other groups, including the numerous GSI data measured by the inverse kinematics method was found. Simulations of the measured data were performed with the MCNPX (Bertini and ISABEL options), CEM03.02, INCL4.2+ABLA, INCL4.5+ABLA07, PHITS, and CASCADE.07 codes. Deviation factors between the calculated and experimental cross sections have been estimated for each target and for the whole energy range covered by our measurements. Two-dimensional diagrams of deviation factor values were produced for estimating the predictive power of every code for intermediate, not measured masses of nuclei-targets and bombarding energies of protons. Further improvements of all tested here codes are recommended. In addition, new measurements at ITEP of nuclide yields from a 208-Pb target irradiated by 500 MeV protons are presented. A good agreement between these new data and the GSI measurements obtained by the inverse kinematics method was found

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arXiv2011

Isospin dependent multifragmentation of relativistic projectiles

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.

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arXiv2010

Tracing a phase transition with fluctuations of the largest fragment size: Statistical multifragmentation models and the ALADIN S254 data

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.

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arXiv2009

Improved modelling of helium and tritium production for spallation targets

Reliable predictions of light charged particle production in spallation reactions are important to correctly assess gas production in spallation targets. In particular, the helium production yield is important for assessing damage in the window separating the accelerator vacuum from a spallation target, and tritium is a major contributor to the target radioactivity. Up to now, the models available in the MCNPX transport code, including the widely used default option Bertini-Dresner and the INCL4.2-ABLA combination of models, were not able to correctly predict light charged particle yields. The work done recently on both the intranuclear cascade model INCL4, in which cluster emission through a coalescence process has been introduced, and on the de-excitation model ABLA allows correcting these deficiencies. This paper shows that the coalescence emission plays an important role in the tritium and $^3He$ production and that the combination of the newly developed versions of the codes, INCL4.5-ABLA07, now lead to good predictions of both helium and tritium cross sections over a wide incident energy range. Comparisons with other available models are also presented.

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arXiv2009

Isotopic Dependence of the Caloric Curve

Isotopic effects in projectile fragmentation at relativistic energies have been studied with the ALADIN forward spectrometer at 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. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z ratio of the produced spectator sources, consistent with predictions for expanded systems. Consequences for the proposed interpretation of chemical breakup temperatures as representing the limiting temperatures predicted by microscopic models are discussed.

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arXiv2009

Isotopic Dependence of the Nuclear Caloric Curve

The A/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of 124Sn and radioactive beams of 124La and 107Sn 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 (ΔT \approx 0.6 MeV) appear for residue production near the onset of multifragmentation.

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arXiv2008

Production of medium-mass neutron-rich nuclei in reactions induced by 136Xe projectiles at 1 A GeV on a beryllium target

Production cross sections of medium-mass neutron-rich nuclei obtained in the fragmentation of 136Xe projectiles at 1 A GeV have been measured with the FRagment Separator (FRS) at GSI. 125Pd was identified for the first time. The measured cross sections are compared to 238U fission yields and model calculations in order 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.

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arXiv2008

Experimental investigation of the residues produced in the 136Xe+Pb and 124Xe+Pb fragmentation reactions at 1 A GeV

This paper presents the nuclide cross sections and the longitudinal velocity distributions of residues produced in the reactions of 136Xe and 124Xe at 1 A GeV in a lead target, measured at the high-resolution magnetic spectrometer, the Fragment Separator (FRS) of GSI. The data cover a broad range of isotopes of the elements between Z = 3 and Z = 56 for 136Xe and between Z = 5 and Z = 55 for 124Xe, reaching down to cross sections of a few microbarns. The velocity distributions exhibit a Gaussian shape for masses above A = 20, while more complex behaviour is observed for lighter masses. The isotopic distributions for both reactions preserve a memory on the projectile N/Z ratio over the whole residue mass range.

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arXiv2007

N/Z Dependence of Projectile Fragmentation

The N/Z dependence of projectile fragmentation at relativistic energies has been studied in a recent experiment at the GSI laboratory with the ALADiN forward spectrometer coupled to the LAND neutron detector. Besides a primary beam of 124Sn, also secondary beams of 124La and 107Sn delivered by the FRS fragment separator have been used in order to extend the range of isotopic compositions of the produced spectator sources. With the achieved mass resolution of ΔA/A \approx 1.5%, lighter isotopes with atomic numbers Z \le 10 are individually resolved. The presently ongoing analyses of the measured isotope yields focus on isoscaling and its relation to the properties of hot fragments at freeze-out and on the derivation of chemical freeze-out temperatures which are found to be independent of the isotopic composition of the studied systems. The latter result is at variance with the predictions for limiting temperatures as obtained with finite-temperature Hartree-Fock calculations.

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