arXiv subjects

J. L. Rodríguez-Sánchez

Publications and source records attributed to J. L. Rodríguez-Sánchez.

At least 19 recordsLinked to original sources

arXiv2026

Probing high-momentum components in $^{16}$O via zero-degree $(p,d)$ cross-section ratios

The $^{16}$O$(p,d)^{15}$O reaction was measured at zero degrees for incident-proton energies of 403, 604, 907 and 1209 MeV. Cross-section ratios for the 6.18-MeV (3/2$^-$) and 5.24-MeV (5/2$^+$) excited-state transitions, normalized to the ground-state transition, were previously reported in Wang et al., Phys. Lett. B 879, 140563 (2026), doi:10.1016/j.physletb.2026.140563, together with their implications for high-momentum neutron components in $^{16}$O. The present work extends that study by providing additional experimental and data-analysis details, and by reporting for the first time the ratio $R_{7.3}$, defined as the cross section populating the 7.28-MeV (7/2$^+$) state relative to that for the ground state. The positive-parity state ratios exhibit a pronounced momentum dependence, consistent with representative variational Monte Carlo trends.

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arXiv2026

Performance of the Particle-Identification Silicon-Telescope Array Coupled with the VAMOS++ Magnetic Spectrometer

The Particle-Identification Silicon-Telescope Array (PISTA) is a new detection system designed for high-resolution studies of the fission process induced by multi-nucleon transfer in inverse kinematics. It is specifically optimized for experiments with the VAMOS++ magnetic spectrometer at GANIL (Grand Accélérateur National d'Ions Lourds). The array comprises eight trapezoidal $Δ$E-E silicon telescopes arranged in a corolla configuration. Each telescope integrates two single-sided stripped silicon detectors, enabling target-like recoil identification, energy loss measurements, and trajectory reconstruction. Positioned in close proximity to the target, PISTA's compact geometry achieves high-efficiency tracking of target-like recoils produced in multi-nucleon transfer reactions at Coulomb barrier energies. The spatial segmentation of the array allows precise determination of the mass and charge of the target-like nucleus, and excitation energy of fissioning systems. This work presents the particle identification and excitation energy reconstruction performances for the interactions of $^{238}$U beam with $^{12}$C target. An excitation energy resolution of 800 keV (FWHM) was determined together with mass resolution of 1.1% (FWHM). The combination of PISTA and VAMOS++ magnetic spectrometer enables unprecedented investigations of the fission process as a function of the excitation energy of the fissioning nucleus, particularly for exotic systems produced in transfer-induced reactions.

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arXiv2025

Excitation Spectra of the ${}^{12}{\rm C}(p,d)$ Reaction near the $η'$-Meson Emission Threshold Measured in Coincidence with High-Momentum Protons

The missing mass of the ${}^{12}{\rm C}(p,d)$ reaction has been measured near the $η'$-meson emission threshold in coincidence with a high-momentum proton to selectively collect $η'$-${}^{11}{\rm C}$ mesic nucleus formation events at GSI, Germany. A 2.5 GeV proton excites a carbon nucleus to form an $η'$-mesic nucleus emitting a deuteron forward with an energy of $\sim 1.6$ GeV. The deuteron is momentum-analyzed by the Fragment Separator used as a high-resolution spectrometer to deduce the excitation energy of the residual system. The large-acceptance detector WASA surrounding the target identifies high-momentum protons emitted in the decay of the $η'$-mesic nucleus. The measured semi-exclusive spectrum exhibits structures below the threshold though the statistical significance is limited. The spectrum is fitted by theoretically calculated spectra varying optical-potential parameters of the $η'$-nucleus interaction. The analysis results indicate $η'$-mesic nuclei formation for the real potential depth of $\sim -61$ MeV with a local statistical significance of $3.5 σ$ and, taking into account the look-elsewhere effect, a global significance of $2.1 σ$.

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arXiv2025

Exploring shell effects in fission yields of neutron-deficient Th, Ac, and Ra isotopes near N=126

Studies of nuclear fission over recent decades have led to a well-defined mapping of neutron and proton shell effects across the nuclear chart, particularly within the valley of stability. These shell effects play a crucial role in driving the asymmetric splitting of fissioning nuclei, as reflected in fission yields that are strongly influenced by spherical and deformed shell closures. In the actinide region, the existence of two primary fission modes, standard I and standard II, has been well-established. These fission modes are associated with the proton (neutron) shells at $Z=52$ ($N=82$) and $Z=56$ ($N=88$), respectively. Recently, a new proton shell around $Z=36$ has been found for the lighter fission fragments of pre-actinide nuclei. This discovery demonstrates that as we expand fission studies towards more exotic regions of the nuclear chart, new shell structures emerge. In this proposal, we aim to explore for the first time the most neutron-deficient isotopes of Th, Ac, and Ra. This region offers a unique opportunity to investigate stabilization effects around the spherical neutron shell $N=50$. To achieve this, we plan to use a primary beam of $^{238}$U at 1~GeV/u together with the Fragment Separator (FRS) to produce secondary beams of $^{213-216}$Th, $^{209-214}$Ac and $^{207-213}$Ra. For the investigation of the fission process, we will use the experimental methodology successfully applied in the S415, S438, and S455 experiments, being a continuation of those studies. Fission will be induced by electromagnetic-excitation (Coulex) reactions in inverse kinematics on an active target composed of Pb and C foils. The resulting fission fragments, together with emitted neutrons, will be measured using the R$^3$B experimental setup, which allows for complete kinematic measurements.

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arXiv2025

Performance of newly constructed plastic scintillator barrel in the WASA-FRS experiments and evaluation of radiation damage effects on multi-pixel photon counter

A barrel-shaped plastic scintillation counter with Multi-Pixel Photon Counter (MPPC) readout has been developed and operated in the first WASA-FRS experimental campaign at GSI. The detector was used to measure charged particles emitted from reactions induced by a 2.5 GeV proton beam incident on a carbon target, providing particle identification in combination with momentum reconstruction in a 1 T magnetic field. The performance of this detector, particularly its response to energy deposition and time resolution, was systematically investigated as a function of count rate and total number of irradiating protons. A time resolution of 45-75 ps ($σ$), depending on the energy deposition, was achieved. Stable performance was maintained under high-rate conditions up to 1.35 MHz per single counter, with no significant degradation in either signal amplitude or timing response. Radiation-induced damage to the MPPCs was observed primarily as a reduction in signal amplitude, with approximately $35\%$ decrease at an estimated 1 MeV neutron-equivalent fluence of $2.4 \times 10^{10}$ cm$^{-2}$.

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arXiv2025

Probing $Λ$ potential at high and low densities via $^3_Λ$H production in C+C reactions

The production of Lambda hyperons and light hypernuclei in heavy-ion collisions provides critical insights into the nuclear equation of state (EoS) and hyperon interactions in dense matter, addressing the longstanding ``hyperon puzzle'' in neutron star physics. Using the INCL+ABLA and AMPT-HC models, we systematically investigate C+C collisions at beam energies of 1.1 and 1.9 GeV/nucleon to explore the sensitivity of hyperon and hypernuclei yields to the EoS and hyperon potential. Our results reveal that Lambda hyperon production is predominantly influenced by the nuclear EoS, while light hypernuclei formation (e.g., $^3_Λ$H) exhibits stronger sensitivity to the hyperon potential at high/low densities with the incident beam energies of 1.1/1.9 GeV. The study provides a framework for future experiments at facilities like HIAF and FAIR/GSI to resolve the hyperon puzzle, thus advancing our understanding of quantum chromodynamics in high-density regimes.

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arXiv2025

Neural network-based prediction of particle-induced fission cross sections for r-process nucleosynthesis trained with dynamical reaction models

Large-scale computations of fission properties play a crucial role in nuclear reaction network calculations simulating rapid neutron-capture process (r-process) nucleosynthesis. Due to the large number of fissioning nuclei contributing to the r-process, a description of particle-induced fission reactions is computationally challenging. In this work, we use theoretical calculations based on the INCL+ABLA models to train neural networks (NN). The results for the prediction of proton-induced spallation reactions, in particular fission, utilizing a large variety of NN models across the hyper-parameter space are presented, which are relevant for r-process calculations.

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arXiv2025

Exploring total fission cross sections of neutron- and proton-induced reactions of exotic nuclei at relativistic energies using the INCL-ABLA++ models

Spallation-induced fission reactions, in combination with state-of-the-art dynamical calculations, provide a robust framework for studying the nuclear dissipation mechanism in nuclear matter over a wide range of deformations. Experimental datasets of neutron- and proton-induced fission, accumulated over the last decades, cover a wide range of nuclei from the pre-actinide to the actinide region. In this work, these datasets are used to benchmark the dynamical Liège intranuclear cascade model INCL++ integrated with the ABLA++ de-excitation code, which has been improved by updating the calculation of particle separation energies to the atomic mass evaluation (AME2020) and incorporating phenomenological corrections to enhance the description of fission-barrier heights. The results show good agreement with the available experimental data of total fission cross sections induced by protons and neutrons, thereby confirming the applicability and predictive capability of these models. Moreover, the improved framework is used to investigate the fission cross sections of exotic heavy fissile nuclei, far from the valley of stability, with masses $A > 155$.

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arXiv2025

Study of medium-mass and heavy hypernuclei produced through spallation and fission reactions in inverse kinematics

Innovative experiments using the inverse kinematics technique to accelerate light, medium-mass, and heavy nuclei at relativistic energies have become excellent tools to produce and study hypernuclei. In this work, we investigate hypernuclei created in spallation reactions, where multifragmentation, particle evaporation, and fission processes play an important role in the formation of final hypernuclei residues. For the description of spallation reactions, we couple the Liège intranuclear cascade model, extended recently to the strange sector, to a new version of the ablation (ABLA) model that accounts for the evaporation of Λ-particles from hot hyperremnants produced during the intranuclear cascade stage. These state-of-the art models are then used to study the production of hypernuclei close to the drip lines through spallation-evaporation and fission reactions. Moreover, recent results obtained for the study of hypernuclei dynamics, in particular, for the constraint of the viscosity parameter involved in hyperfission reactions are also presented.

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arXiv2024

Examining the potential synthesis of new elements with $^{294}$Og

In the relentless pursuit of expanding the periodic table, the discovery of element 119 remains elusive, despite two decades of dedicated research efforts. The traditional fusion-evaporation approach, although fruitful in the past, now appears to be approaching its operational limits. This scenario sets the stage for considering innovative methodologies essential for further advancements in the field of superheavy elements. Here, we introduce a pioneering strategy aimed at synthesizing element 119 by adapting and extending the nuclear reaction processes previously successful in producing element $^{294}$Og. This involved the fusion of $^{48}$Ca and $^{249}$Cf. Building on this, our novel approach incorporates an additional reactive target -- specifically, hydrogen -- positioned strategically behind the $^{249}$Cf. This configuration is designed to facilitate an immediate secondary reaction of the nascent $^{294}$Og with hydrogen, potentially forging new pathways to element 119. Preliminary insights also suggest that employing isotopes like deuterium or helium-3 as targets may not only enhance the production rates of element 119 but might also pave the way for the synthesis of even heavier elements, extending up to elements 120 and 121. We delve into the technicalities and feasibility of employing a dual-target method using a $^{48}$Ca beam, exploring new horizons in the quest for the superheavy unknown.

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arXiv2023

Constraint of the Nuclear Dissipation Coefficient in Fission of Hypernuclei

Experimental studies of nuclear fission induced by fusion, transfer, spallation, fragmentation, and electromagnetic reactions in combination with state-of-the-art calculations are successful to investigate the nuclear dissipation mechanism in normal nuclear matter, containing only nucleons. The dissipation mechanism has been widely studied by the use of many different fission observables and nowadays the dissipation coefficients involved in transport theories are well constrained. However, the existence of hypernuclei and the possible presence of hyperons in neutron stars make it necessary to extend the investigation of the nuclear dissipation coefficient to the strangeness sector. In this Letter, we use fission reactions of hypernuclei to constrain for the first time the dissipation coefficient in hypernuclear matter, observing that this coefficient increases a factor of 6 in presence of a single $Λ$-hyperon with respect to normal nuclear matter.

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arXiv2022

Quasi-free (p,2p) reactions in inverse kinematics for studying the fission yield dependence on temperature

Despite the recent experimental and theoretical progress in the investigation of the nuclear fission process, a complete description still represents a challenge in nuclear physics because it is a very complex dynamical process, whose description involves the coupling between intrinsic and collective degrees of freedom, as well as different quantum-mechanical phenomena. To improve on the existing data on nuclear fission, we produce fission reactions of heavy nuclei in inverse kinematics by using quasi-free (p,2p) scattering, which induce fission through particle-hole excitations that can range from few to ten's of MeV. The measurement of the four-momenta of the two outgoing protons allows to reconstruct the excitation energy of the fissioning compound nucleus and therefore to study the evolution of the fission yields with temperature. The realization of this kind of experiment requires a complex experimental setup, providing full isotopic identification of both fission fragments and an accurate measurement of the momenta of the two outgoing protons. This was realized recently at the GSI/FAIR facility and here some preliminary results are presented.

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arXiv2022

Comprehensive investigation of fission yields by using spallation- and (p,2p)-induced fission reactions in inverse kinematics

In the last decades, measurements of spallation, fragmentation and Coulex induced fission reactions in inverse kinematics have provided valuable data to accurately investigate the fission dynamics and nuclear structure at large deformations of a large variety of stable and non-stable heavy nuclei. To go a step further, we propose now to induce fission by the use of quasi-free (p,2p) scattering reactions in inverse kinematics, which allows us to reconstruct the excitation energy of the compound fissioning system by using the four-momenta of the two outgoing protons. Therefore, this new approach might permit to correlate the excitation energy with the charge and mass distributions of the fission fragments and with the fission probabilities, given for the first time direct access to the simultaneous measurement of the fission yield dependence on temperature and fission barrier heights of exotic heavy nuclei, respectively. The first experiment based on this methodology was realized recently at the GSI/FAIR facility and a detailed description of the experimental setup is given here.

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arXiv2020

Systematic reduction of the proton-removal cross section in neutron-rich medium-mass nuclei

Single neutron- and proton-removal cross sections have been systematically measured for 72 medium-mass neutron-rich nuclei around Z=50 and energies around 900A MeV using the FRagment Separator (FRS) at GSI. Neutron-removal cross sections are described by considering the knock-out process together with initial- and final-state interactions. Proton-removal cross sections are, however, significantly smaller than predicted by the same calculations. The observed difference can be explained as due to the knockout of short-correlated protons in neutron-proton dominating pairs.

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arXiv2020

Performance recovery of long CsI(Tl) scintillator crystals with APD-based readout

CALIFA is the high efficiency and energy resolution calorimeter for the R3B experiment at FAIR, intended for detecting high energy light charged particles and gamma rays in scattering experiments, and is being commissioned during the Phase-0 experiments at FAIR, between 2018 and 2020. It surrounds the reaction target in a segmented configuration with 2432 detection units made of long CsI(Tl) finger-shaped scintillator crystals. CALIFA has a 10 year intended operational lifetime as the R3B calorimeter, necessitating measures to be taken to ensure enduring performance. In this paper we present a systematic study of two groups of 6 different detection units of the CALIFA detector after more than four years of operation. The energy resolution and light output yield are evaluated under different conditions. Tests cover the aging of the first detector units assembled and investigates recovery procedures for degraded detection units. A possible reason for the observed degradation is given, pointing to the crystal-APD coupling.

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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

Missing-mass spectroscopy of the ${}^{12}{\rm C}(p,d)$ reaction near the $η^\prime$-meson production threshold

Excitation-energy spectra of $^{11}$C nuclei near the $η^\prime$-meson production threshold have been measured by missing-mass spectroscopy using the $^{12}$C($p$,$d$) reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce $η^\prime$ meson bound states in $^{11}$C nuclei. Deuterons emitted at $0^\circ$ in the reaction have been momentum-analyzed by the fragment separator (FRS) used as a high-resolution spectrometer. No distinct structure due to the formation of $η^\prime$-mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of $η^\prime$-mesic states are determined, and thereby a constraint imposed on the $η^\prime$-nucleus interaction is discussed.

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arXiv2016

Measurement of excitation spectra in the ${}^{12}$C$(p,d)$ reaction near the $η'$ emission threshold

Excitation spectra of $^{11}$C were measured in the $^{12}$C$(p,d)$ reaction near the $η'$ emission threshold. A proton beam extracted from the synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinged on a carbon target. The momenta of deuterons emitted at 0 degrees were precisely measured with the fragment separator FRS operated as a spectrometer. In contrast to theoretical predictions on the possible existence of deeply bound $η'$ mesic states in carbon nuclei, no distinct structures were observed associated with the formation of bound states. The spectra were analyzed to set stringent constraints on the formation cross section and on the hitherto barely-known $η'$-nucleus interaction.

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