Dr Alexis Diaz-Torres


Reader in Theoretical Nuclear Physics
Dr. rer. nat. (Justus-Liebig-University Giessen, Germany), MSc & BSc (InSTEC in Havana, Cuba), FHEA, FInstP
+44 (0)1483 689855
01 BB 03

Academic and research departments

Department of Physics.

Biography

Areas of specialism

Theoretical Nuclear Physics; Nuclear Structure and Reaction Dynamics; Computational Physics

University roles and responsibilities

  • Leader of the Maths & Physics Programmes
  • Module Leader of Mathematical and Computational Physics (PHY1038)
  • Module Leader of Maths and Physics MPhys Project (PHYM060)

    Research

    Research interests

    Research projects

    - OWL: a code for the two-center shell model with spherical Woods-Saxon potentials, A. Diaz-Torres, Computer Physics Communications 224 (2018) 381-386.

    - PLATYPUS:  a code for reaction dynamics of weakly bound nuclei at near-barrier energies within a classical dynamical model, A. Diaz-Torres, Computer Physics Communications 182 (2011) 1100-1104.

    Supervision

    Postgraduate research supervision

    My teaching

    My publications

    Highlights

    Most of my publications can be downloaded from ResearchGate (https://www.researchgate.net/profile/Alexis_Diaz-Torres2). Please find below some ePrints at Surrey. A complete list of my publications can be found on ORCID (https://orcid.org/0000-0001-6234-9353).

    Publications

    Iain Lee, ALEXIS DIAZ-TORRES (2022)Coherence dynamics in low-energy nuclear fusion, In: Physics letters. B Nuclear, elementary particle and high-energy physics. Elsevier

    Low-energy nuclear fusion reactions have been described using a dynami-cal coupled-channels density matrix method, based on the theory of open quantum systems. For the first time, this has been combined with an energy projection method, permitting the calculation of energy resolved fusion probabilities. The results are benchmarked against calculations using stationary Schrödinger dynamics and show excellent agreement. Calculations of entropy, energy dissipation and coherence were conducted, demonstrating the capability of this method. It is evident that the presence of quantum decoherence does not affect fusion probability. This framework provides a basis for quantum thermodynamic studies using thermal environments.

    TERENCE VOCKERODT, ALEXIS DIAZ TORRES (2021)Calculating the S-matrix of low energy heavy-ion collisions using quantum coupled-channel wave-packet dynamics, In: Physical review C American Physical Society

    We investigate the fusion and scattering of a 16 O projectile on 152,154 Sm targets using the time-dependent coupled-channel wave-packet method. We benchmark calculations of the S-matrix elements, fusion cross sections and scattering differential cross sections with those from the time-independent coupled-channel method, and compare the results to experimental data. We find that our time-dependent method and the time-independent method produce quantitatively similar results for the S-matrix elements and fusion cross sections, but our method cannot quantitatively explain the experimental scattering differential cross sections, mainly due to the low maximum number of partial waves produced by the time-dependent method. Nevertheless, the strong agreements between our method and the time-independent method demonstrates that the time-dependent coupled-channel wave-packet method can be used to address fusion reactions for a wide range of energies, with the advantage of being able to extend to time-dependent Hamiltonians for more advanced modelling of nuclear reactions.

    Terry Vockerodt, Alexis Diaz-Torres (2019)Describing heavy-ion fusion with quantum coupled-channels wave-packet dynamics, In: Physical Review C100034606pp. 034606-1 American Physical Society

    We investigate the fusion of 16O and 154Sm with excited states at Coulomb energies using a theoretical dynamical model. The two-body Schrödinger equation is solved using the time-dependent wave-packet coupled-channels method. The wave function of the collective motion and excitations are visualized in both position and momentum space, providing a detailed mechanism of the reaction. We benchmark our calculations of the energy-resolved fusion transmission coefficients with those from the time-independent coupled-channels method. The present results are in good agreement with the time-independent results for a wide range of energies and angular momenta, demonstrating both the reliability of the quantum wave-packet dynamical approach for fusion and its usefulness for providing additional insights into fusion dynamics.

    RG Thomas, DJ Hinde, D Duniec, F Zenke, M Dasgupta, ML Brown, M Evers, LR Gasques, MD Rodriguez, A Diaz-Torres (2008)Entrance channel dependence of quasifission in reactions forming Th-220, In: PHYSICAL REVIEW C77(3)ARTN 03461 AMER PHYSICAL SOC
    DJ Hinde, M Dasgupta, A Diaz-Torres, M Evers (2010)Quantum coherence and decoherence in low energy nuclear collisions: from superposition to irreversibility, In: NUCLEAR PHYSICS A834(1-4)pp. 117C-122C
    A Diaz-Torres, D J Hinde, J A Tostevin, M Dasgupta, L R Gasques (2007)Relating Breakup and Incomplete Fusion of Weakly Bound Nuclei Through a Classical Trajectory Model with Stochastic Breakup, In: Physical Review Letters98(15)

    A classical dynamical model that treats breakup stochastically is presented for low energy reactions of weakly bound nuclei. The three-dimensional model allows a consistent calculation of breakup, incomplete, and complete fusion cross sections. The model is assessed by comparing the breakup observables with continuum discretized coupled-channel quantum mechanical predictions, which are found to be in reasonable agreement. Through the model, it is demonstrated that the breakup probability of the projectile as a function of its distance from the target is of primary importance for understanding complete and incomplete fusion at energies near the Coulomb barrier.

    Alexis Diaz Torres (2019)Reaction dynamics of complex nuclei at low energy within a molecular picture, In: Frontiers in Nuclear and Particle Physics2pp. 132-149 Bentham Science Publishers

    Some of my recent works on the two-center shell model and its application to describing low-energy nuclear collisions within time-dependent approaches are reviewed and a perspective for their further use is given.

    C Beck, N Keeley, A Diaz-Torres (2008)Cluster model for near-barrier fusion induced by weakly bound and halo nuclei, In: P Demetriuo, SV Harissopulos (eds.), FRONTIERS IN NUCLEAR STRUCTURE, ASTROPHYSICS, AND REACTIONS1012pp. 233-237
    A Diaz-Torres, DJ Hinde, M Dasgupta, GJ Milburn, JA Tostevin (2009)Coupled-Channels Approach for Dissipative Quantum Dynamics in Near-Barrier Collisions, In: KE Rehm, BB Back, H Esbensen, CJ Lister (eds.), FUSION 081098pp. 44-51

    A novel quantum dynamical model based on the dissipative quantum dynamics of open quantum systems is presented. It allows the treatment of both deep-inelastic processes and quantum tunneling (fusion) within a fully quantum mechanical coupled-channels approach. Model calculations show the transition from pure state (coherent) to mixed state (decoherent and dissipative) dynamics during a near-barrier nuclear collision. Energy dissipation, due to irreversible decay of giant-dipole excitations of the interacting nuclei, results in hindrance of quantum tunneling

    L Yang, C.J Lin, H Yamaguchi, Jin Lei, P.W Wen, M Mazzocco, N.R Ma, L.J Sun, D.X Wang, G.X Zhang, K Abe, S.M Cha, K.Y Chae, ALEXIS DIAZ TORRES, J.L Ferreira, S Hayakawa, H.M Jia, D Kahl, A Kim, M.S Kwag, M La Commara, R Navarro Perez, C Parascandolo, D Pierroutsakou, J Rangel, Y Sakaguchi, C Signorini, E Strano, X.X Xu, F Yang, Y.Y Yang, G.L. Zhang, F.P Zhong, J Lubian (2021)Insight into the reaction dynamics of proton drip-line nuclear system .sup.17F+.sup.58Ni at near-barrier energies, In: Physics Letters. B813 Elsevier B.V

    The mechanism of reactions with weakly-bound proton-rich nuclei at energies near the Coulomb barrier is a long-standing open question owing to the paucity of experimental data. In this study, a complete kinematics measurement was performed for the proton drip-line nucleus .sup.17F interacting with .sup.58Ni at four energies near the Coulomb barrier. Thanks to the powerful performance of the detector array, exhaustive information on the reaction channels, such as the differential cross sections for quasielastic scattering, exclusive and inclusive breakup, as well as for fusion-evaporation protons and alphas, was derived for the first time. The angular distributions of quasielastic scattering and exclusive breakup can be described reasonably well by the continuum-discretized coupled-channels calculations. The inclusive breakup was investigated using the three-body model proposed by Ichimura, Austern, and Vincent, and results indicate the non-elastic breakup is the dominant component. The total fusion cross sections were determined by the fusion-evaporation protons and alphas. Based on the measured exclusive breakup data, the analysis of the classical dynamical simulation code PLATYPUS demonstrates that the incomplete fusion plays a minor role. Moreover, compared with .sup.16O+.sup.58Ni, both the reaction and total fusion cross sections of .sup.17F+.sup.58Ni exhibit an enhancement in the sub-barrier energy region, which mainly arises from couplings to the continuum states. This work indicates that the information of full reaction channels is crucially important to comprehensively understand the reaction mechanisms of weakly bound nuclear systems.

    RAFAEL VAN DEN BOSSCHE, ALEXIS DIAZ TORRES (2020)Production of transuranium isotopes in 20 Ne-induced incomplete fusion reactions, In: PHYSICAL REVIEW C102064618 American Physical Society

    Using a semiclassical dynamical model that combines a classical trajectory model with stochastic breakup with a dynamical fragmentation theory treatment of two-body clusterization and decay of a projectile, results are presented for 20 Ne-induced incomplete fusion reactions for the production of superheavy elements. Targets include 247,248,250 Cm and 251,252,254 Cf, and results include angular, excitation energy, and angular momentum distributions in addition to total integrated cross sections for heavy incomplete fusion products. The results show that at Coulomb energies, the studied Cf isotopes are generally the more favorable choice of target over the studied Cm isotopes for the production of 'colder' and more stable 263 Lr, 263,264,266 Rf, and 265 Db isotopes through the incomplete fusion mechanism. Also presented are evaporation residue cross sections for the dominant primary incomplete fusion products of each of the six reactions: 263,264,266 Rf and 267,268,270 Sg, as well as for the primary incomplete fusion products 269,270,272 Bh.

    Alexis Diaz Torres (2017)OWL: a code for the two-center shell model with spherical Woods-Saxon potentials, In: Computer Physics Communications224pp. 381-386 Elsevier

    A Fortran-90 code for solving the two-center nuclear shell model problem is presented. The model is based on two spherical Wood-Saxon potentials and the potential separable expansion method. It describes the single-particle motion in low-energy nuclear collisions, and is useful for characterizing a broad range of phenomena from fusion to nuclear molecular structures.

    A. Diaz-Torres, D. J. Hinde, J. A. Tostevin, M. Dasgupta, L. R. Gasques (2007)Relating Breakup and Incomplete Fusion of Weakly Bound Nuclei through a Classical Trajectory Model with Stochastic Breakup, In: Physical Review Letters98(152701)

    A classical dynamical model that treats breakup stochastically is presented for low energy reactions of weakly bound nuclei. The three-dimensional model allows a consistent calculation of breakup, incomplete, and complete fusion cross sections. The model is assessed by comparing the breakup observables with continuum discretized coupled-channel quantum mechanical predictions, which are found to be in reasonable agreement. Through the model, it is demonstrated that the breakup probability of the projectile as a function of its distance from the target is of primary importance for understanding complete and incomplete fusion at energies near the Coulomb barrier.

    M Dasgupta, DJ Hinde, A Diaz-Torres, B Bouriquet, CI Low, GJ Milburn, JO Newton (2007)Beyond the coherent coupled channels description of nuclear fusion, In: PHYSICAL REVIEW LETTERS99(19)ARTN 19270 AMER PHYSICAL SOC
    FA Souza, N Carlin, C Beck, N Keeley, A Diaz-Torres, R Liguori Neto, C Siqueira-Mello, MM de Moura, MG Munhoz, RAN Oliveira, MG Del Santo, AAP Suaide, EM Szanto, AS de Toledo (2010)Li-6 direct breakup lifetimes, In: NUCLEAR PHYSICS A834(1-4)pp. 420C-423C
    Gurgen Adamian, Nikolai Antonenko, Alexis Diaz-Torres, Sophia Heinz (2020)How Does One Extend the Chart of Nuclides?, In: Nuclear Physics News30(4)pp. 22-26 Taylor & Francis

    Nuclear physicists all over the world are searching for new exotic nuclei. But their ambitions are being hindered by the lack of effective state-of-the-art methods for laboratory nucleosynthesis. Activities are ongoing in many places to find new pathways for production and detection of exotic nuclei. But how promising are these efforts? Here we give an overview of the ongoing worldwide activities. Objects of desire Figure 1. The current Karlsruhe Chart of Nuclides, issued in 2018, contains almost 3300 different isotopes of 118 elements. The expected limits of nuclear stability (driplines) are indicated by dashed lines. Toward the driplines, the nuclei become more and more exotic. How and where are the chemical elements created in the universe? Which nuclear reactions determine the evolution and destiny of stars? And what is the nature of the still obscure nuclear force? Such fundamental questions occupy nuclear physicists. The answers are mostly hidden in the properties of exotic nuclei, like their binding energy, half-life or shape. Exotic nuclei are unstable and do not occur in our natural environment on Earth, therefore we have to produce them artificially in the lab. This is what nuclear physicists have been doing for many decades. Meanwhile, we know of the existence of more than 3000 different isotopes of 118 elements (Fig.1), with about 90 percent of them being man-made [1]. Each nuclide has its own individual combination of protons and neutrons and is governed by the sensitive interplay between the attractive nuclear force and the repulsive Coulomb force which determines its properties. Model predictions indicate that another 4000 isotopes are still awaiting their discovery, with the vastest unexplored territory located on the neutron-rich side in the upper half of the nuclide chart. Most of the astrophysical rapid neutron capture process (r-process), which is assumed to be responsible for the production of the heavy elements in stellar explosions, proceeds through this unknown territory. By studying the properties of nuclei along the r-process path we can understand the astrophysical synthesis of the heavy elements and their abundances in nature. It is still obscure where the r-process ends in the upper part of the nuclide chart. Presumably it penetrates deep into the territory of neutron-rich superheavy nuclei. New magic neutron and proton numbers are predicted in this region at N=184, Z=114 or 120-126 creating an " island of stability ". Nuclei on this " island " are expected to have higher fission barriers, resulting in an enhanced stability against fission. Is the " island of stability " the endpoint of the r-process path?

    DJ Hinde, RG Thomas, R du Rietz, A Diaz-Torres, M Dasgupta, ML Brown, M Evers, LR Gasques, R Rafiei, MD Rodriguez (2008)Disentangling effects of nuclear structure in heavy element formation, In: PHYSICAL REVIEW LETTERS100(20)ARTN 20270 AMER PHYSICAL SOC
    A Diaz-Torres, LR Gasques, M Wiescher (2007)Effects of nuclear molecular configurations on the astrophysical S-factor for O-16+O-16, In: PHYSICS LETTERS B652(5-6)pp. 255-258 ELSEVIER SCIENCE BV
    A Diaz-Torres (2010)Modelling incomplete fusion dynamics of weakly bound nuclei at near-barrier energies, In: JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS37(7)ARTN 07510 IOP PUBLISHING LTD
    A Diaz-Torres, LR Gasques, M Wiescher (2008)ASTROPHYSICAL S-FACTOR FOR O-16+O-16 WITHIN THE ADIABATIC MOLECULAR PICTURE, In: INTERNATIONAL JOURNAL OF MODERN PHYSICS E-NUCLEAR PHYSICS17(10)pp. 2194-2198
    Iain Lee, Alexis Diaz-Torres (2019)Populating high spin states of a compound nucleus with the incomplete fusion mechanism: the effectiveness of heavy projectiles, In: JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS IOP PUBLISHING LTD

    Using a classical dynamical reaction model, angular momentum (____textit{L}) values of a compound nucleus due to incomplete fusion at energies near and above the Coulomb barrier are studied. In this model, a projectile consisting of two cluster nuclei is fired at a stationary target nucleus. After breakup of the projectile due to Coulombic and nuclear forces, an ____(____alpha____)-cluster fuses with a ____textsuperscript{208}Pb target, forming an excited ____textsuperscript{212}Po compound nucleus. Results show that all incomplete fusion reactions produced higher angular momentum in the compound nucleus compared to a direct beam of ____(____alpha____) particles at the same incident energy. The highest angular momentum values produced in ____textsuperscript{212}Po for near and above Coulomb barrier energies were obtained using a ____textsuperscript{20}Ne projectile, at 16____(____hbar____) and 40____(____hbar____) respectively. This produced 25____% and 50____% ____textit{L} values above the next highest-Z projectile used, ____textsuperscript{8}Be, respectively.

    LR Gasques, M Dasgupta, DJ Hinde, T Peatey, A Diaz-Torres, JO Newton (2006)Isomer ratio measurements as a probe of the dynamics of breakup and incomplete fusion, In: PHYSICAL REVIEW C74(6)ARTN 06461 AMERICAN PHYSICAL SOC
    Alexis Diaz Torres (2017)Molecular Structure in Slow Nuclear Collisions, In: S Wolf-Udo (eds.), Nuclear Particle Correlations and Cluster Physicspp. 447-470 World Scientific Publishing

    A modern two-center shell model and its usefulness for addressing low-energy reaction dynamics of light and heavy nuclei are presented. A perspective for further developments in nuclear reaction theory is given.

    A Diaz-Torres (2010)Absence of decoherence in the complex-potential approach to nuclear scattering, In: PHYSICAL REVIEW C81(4)ARTN 04160 AMER PHYSICAL SOC
    A Diaz-Torres, DJ Hinde, JA Tostevin, M Dasgupta, LR Gasques (2007)Relating breakup and incomplete fusion of weakly bound nuclei through a classical trajectory model with stochastic breakup, In: PHYSICAL REVIEW LETTERS98(15)ARTN 1pp. ?-? AMERICAN PHYSICAL SOC
    M Dasgupta, DJ Hinde, A Diaz-Torres, DH Luong (2009)Towards a Consistent Understanding of Near-barrier Reactions, In: KE Rehm, BB Back, H Esbensen, CJ Lister (eds.), FUSION 081098pp. 11-17
    Alexis Diaz Torres, Daanish Quraishi (2018)Effects of unconventional breakup modes on incomplete fusion of weakly bound nuclei, In: Physical Review C97 American Physical Society

    The incomplete fusion dynamics of 6Li + 209Bi collisions at energies above the Coulomb barrier is investigated. The classical dynamical model implemented in the {____sc platypus} code is used to understand and quantify the impact of both 6Li resonance states and transfer-triggered breakup modes (involving short-lived projectile-like nuclei such as 8Be and 5Li) on the formation of incomplete fusion products. Model calculations explain the experimental incomplete-fusion excitation function fairly well, indicating that (i) delayed direct breakup of 6Li reduces the incomplete fusion cross-sections, and (ii) the neutron-stripping channel practically determines those cross-sections.

    G. S. Li, Y. D. Fang, A. Diaz-Torres, M. L. Liu, N. T. Zhang, X. H. Zhou, Y. H. Zhang, J. G. Wang, B. S. Gao, Y. H. Qiang, S. Guo, S. C. Wang, Z. Y. Zhang, J. F. Huang, K. L. Wang, Y. Zheng, S. Mukherjee (2019)Isomer yield ratios in 184Re from the 9Be + 181Ta reaction, In: Physical Review C99(5)054617pp. 054617-1 American Physical Society

    The isomer yield ratios of 184R in the incomplete fusion of the 9Be + 181Ta system were measured at energies around the Coulomb barrier, using online activation followed by offline γ-ray spectroscopy method. The PLATYPUS code that is based on a classical dynamical model is employed to analyze the measurements. By applying a phenomenological approach, model calculation managed to fairly reproduce the order of magnitude of the yield ratios at above barrier energies. Through the study, it is shown that the PLATYPUS code in conjunction with a phenomenological analysis can provide a reasonable explanation of isomer yield ratios resulted from incomplete fusion of weakly bound projectiles.

    James Lenton, IAIN GARIAN LEE, ALEXIS DIAZ TORRES (2021)Quantum dynamics of a nucleon in the Fermi accelerator, In: Annals of Physics168624 Elsevier

    The quantum dynamics of a particle in a one-dimensional box with an oscillating wall (the Fermi accelerator) is investigated. The model is applied to the motion of a single nucleon in the mean-field potential of a heavy atomic nucleus whose surface vibrates. By directly solving the time-dependent Schrödinger equation, both the state of the particle and its mean-energy are studied. The effects of the frequency of the wall oscillation on the nucleon’s energy are addressed. Its energy oscillates in phase with the moving wall for all frequencies, showing no chaotic behaviour. There is a large initial peak of the nucleon’s energy as the particle adjusts to the sudden change in the size of the box and a varying relaxation time as it plateaus towards lower energy and a partial equilibrium. Small oscillations in energy continue, since there cannot be a true equilibrium while the wall is moving. The quantum coherence between the different parts of the nucleon’s wave-function in real space is very much preserved. This research lays the foundation for future investigations into quantum tunnelling in the Fermi accelerator.

    Alexis Diaz-Torres, Michael Wiescher (2019)Resonances in Stellar Carbon Fusion, In: A. Formicola, M. Junker, L. Gialanella, G. Imbriani (eds.), Springer Proceedings in Physics - Nuclei in the Cosmos XV219pp. 1-4 Springer International Publishing

    A quantitative study of the astrophysically important sub-barrier fusion of 12C+ 12C is reported. Lowenergy collisions are described in the body-fixed reference frame using wave-packet dynamics within a nuclear molecular picture. In contrast to conventional methods, such as the potential model and the coupled-channels approach, these new calculations reveal three resonant structures in the S-factor, explaining some structures observed in the data. The structures in the data that are not explained are possibly due to cluster effects in the nuclear molecule, which need to be included in the new approach.

    C Beck, N Rowley, P Papka, S Courtin, M Rousseau, FA Souza, N Carlin, F Liguori Neto, MM De Moura, MG Del Santo, AAI Suade, MG Munhoz, EM Szanto, AS De Toledo, N Keeley, A Diaz-Torres, K Hagino (2011)CLUSTER MODEL FOR REACTIONS INDUCED BY WEAKLY BOUND AND/OR EXOTIC HALO NUCLEI WITH MEDIUM-MASS TARGETS, In: INTERNATIONAL JOURNAL OF MODERN PHYSICS E-NUCLEAR PHYSICS20(4)pp. 943-946
    M Dasgupta, LR Gasques, DH Luong, R du Rietz, R Rafiei, DJ Hinde, CJ Lin, M Evers, A Diaz-Torres (2010)Reaction dynamics of weakly bound nuclei at near-barrier energies, In: NUCLEAR PHYSICS A834(1-4)pp. 147C-150C
    G.S Li, M.L Liu, D. Patel, Y.D Fang, X.H Zhou, Y.H Zhang, Alexis Diaz Torres, C.S Palshetkar, J. Lubian, N.T Zhang, J.G Wang, B.S Gao, Y.H Qiang, S. Guo, Y. Zheng, K.L Wang, K.K Zheng, R Li, S. Mukherjee (2019)Fusion reaction studies for the 9Be + 89Y system at above-barrier energies, In: Physical Review C American Physical Society

    Complete fusion (CF) cross section measurement for the weakly bound 9Be projectile interacting with the intermediate mass target 89Y has been extended to energies greater than the fusion barrier, by implementing off-line characteristic γ -ray detection techniques. The available experimental data for the 9Be + 89Y reaction system were compared with the theoretical predictions, using the PLATYPUS code that is based on a classical dynamical model. By introducing the breakup probability that deduced in the literature from the fitting of the experimental data, the model managed to reproduce the CF cross sections of 9Be beam with targets of different atomic mass. Through the study, it is revealed that the extended CF excitation function for the 9Be + 89Y system is consistent with the systematical behavior that the prompt-breakup probability at above-barrier energies is roughly independent of the target in the reactions induced by the same weakly bound projectiles.

    A Diaz-Torres, DJ Hinde, M Dasgupta, GJ Milburn, JA Tostevin (2008)Dissipative quantum dynamics in low-energy collisions of complex nuclei, In: PHYSICAL REVIEW C78(6)ARTN 0pp. ?-? AMER PHYSICAL SOC
    A Diaz-Torres (2006)Dynamical collective potential energy landscape: Its impact on the competition between fusion and quasi-fission in a heavy fusing system, In: L Corradi, E Fioretto, A Gadea, D Ackermann, F Haas, G Pollarolo, F Scarlassara, S Szilner, M Trotta (eds.), FUSION06: Reaction Mechanisms and Nuclear Structure at the Coulomb Barrier853pp. 225-230
    A Diaz Torres, AM Moro (2014)Insights into low-energy elastic scattering of halo nuclei, In: Physics Letters B733pp. 89-92 Elsevier

    Recent measurements of low-energy (quasi)elastic-scattering angular distribution of halo nuclei have shown a strong suppression of the Coulomb-nuclear interference peak. Examining the components of the elastic-scattering differential cross sections for 11Be + 64Zn and 6He + 208Pb at energies near the Coulomb barrier, this appears to be caused by a dramatic phase-change (destructive) of the reduced Coulomb-nuclear interference term due to continuum couplings.

    Rafael Van den Bossche, Alexis Diaz-Torres (2019)Modelling incomplete fusion dynamics of complex nuclei at Coulomb energies, In: Physical Review C100(4)044604pp. 044604-1 American Physical Society

    The incomplete fusion dynamics of ²⁰₁₀Ne + ²⁰⁸₈₂Pb collisions at energies above the Coulomb barrier are investigated using a novel semiclassical dynamical model, which combines a classical trajectory model with stochastic breakup, as implemented in the platypus code, with a dynamical fragmentation theory treatment of two-body clusterization and decay of a projectile. A finite-difference method solution to the time-independent Schrödinger equation in the charge asymmetry coordinate is employed by way of diagonalizing a tridiagonal Hamiltonian matrix with periodic boundary conditions. Results are compared with published experimental values to indicate the success of this new model, and next steps for its development are detailed.

    G.G Adamian, N.V Antonenko, Alexis Diaz Torres, S. Heinz (2019)How to extend the chart of nuclides?, In: EUROPEAN PHYSICAL JOURNAL A56(47) SPRINGER

    In the past 85 years the number of known nuclides increased by more than a factor of ten, resulting in 4000 presently known isotopes of 118 elements. This considerable progress we owe to the discovery of new reaction types along with the development of powerful accelerators and experimental techniques for separation and identification of reaction products. Model predictions indicate that still about 4000 further nuclides are waiting for their discovery. The vastest unexplored territory is located on the neutron-rich side in the upper half of the chart of nuclides and hides the answers to some of the most fundamental questions of nuclear physics like the limits of nuclear stability, element synthesis in the universe or stellar evolution. The access to these nuclei is presently limited by available beam intensities and/or the lack of appropriate methods for their production and identification. The latter concerns particularly new neutron-rich isotopes of transuranium and superheavy elements. To extend this area, the hope is presently based on multinucleon transfer reactions and on the application of fusion reactions with radioactive ion beams. But how promising are these approaches? Based on a survey of present-day knowledge, we will treat the questions where we currently are on our journey towards new territory on the chart of nuclides, how the chances are to gain new territory in the future and which challenges we will have to face.

    C Beck, N Rowley, P Papka, S Courtin, M Rousseau, FA Souza, N Carlin, R Liguori Neto, MM de Moura, MG Del Santo, AAP Suaide, MG Munhoz, EM Szanto, AS de Toledo, N Keeley, A Diaz-Torres, K Hagino (2010)Reaction mechanisms for weakly-bound, stable nuclei and unstable, halo nuclei on medium-mass targets, In: NUCLEAR PHYSICS A834(1-4)pp. 440C-445C
    Guangshun S. Li, Y. D. Fang, X. H. Zhou, ALEXIS DIAZ TORRES, Aman Rohilla, M. L. Liu, N. T. Zhang, Y. H. Zhang, J. G. Wang, B. S. Gao, Y.H Qiang, S. Guo, S. C. Wang, Y-C Zheng, J. Lubian, Hugo O. Soler (2020)Measurement and analysis of the isomeric cross section ratios for the 94 Tc nucleus, In: Physical Review C102(5)

    We report on an isomer yield ratio study of biologically important 94 Tc following the fusion of the 9 Be + 89 Y system, carried out using the offline γ-ray spectroscopy in continuation to the online activation method. The incident beam energies considered are above the Coulomb barrier for the present study. The PLATYPUS model in conjunction with a potential model calculation was employed to analyze the data. An agreement in the order of magnitude between the experimental data and theoretical predictions has been achieved, by applying a phenomenological approach. The approach was further tested with isomer yield ratios of 94 Tc formed through 3 He + 93 Nb reactions. Possible factors that relate to the isomer yield ratios are also presented.

    C Beck, ASI Zafra, A Diaz-Torres, IJ Thompson, N Keeley, FA Souza, L Corradi, E Fioretto, A Gadea, D Ackermann, F Haas, G Pollarolo, F Scarlassara, S Szilner, M Trotta (2006)Near-barrier fusion induced by stable weakly bound and exotic halo light nuclei, In: FUSION06: REACTION MECHANISMS AND NUCLEAR STRUCTURE AT THE COULOMB BARRIER853pp. 384-389
    R Rafiei, R du Rietz, DH Luong, DJ Hinde, M Dasgupta, M Evers, A Diaz-Torres (2010)Mechanisms and systematics of breakup in reactions of Be-9 at near-barrier energies, In: PHYSICAL REVIEW C81(2)ARTN 02460 AMER PHYSICAL SOC
    A Diaz Torres, GG Adamian, VV Sargsyan, NV Antonenko (2014)Energy-shifting formulae yield reliable reaction and capture probabilities, In: Physics Letters B739pp. 348-351 Elsevier

    Predictions of energy-shifting formulae for partial reaction and capture probabilities are compared with coupled channels calculations. The quality of the agreement notably improves with increasing mass of the system and/or decreasing mass asymmetry in the heavy-ion collision. The formulae are reliable and useful for circumventing impracticable reaction calculations at low energies.

    LAURA MOSCHINI, ALEXIS DIAZ TORRES (2021)Tracing the dynamical interplay of low-energy reaction processes of exotic nuclei using a two-center molecular continuum, In: Physics Letters B820136513 Elsevier

    The competition among reaction processes of a weakly-bound projectile at intermediate times of a slow collision has been unraveled. This has been done using a two-center molecular continuum within a semiclassical, time-dependent coupled-channel reaction model. Dynamical probabilities of elastic scattering, transfer and breakup agree with those derived from the direct integration of the time-dependent Schrödinger equation, demonstrating the usefulness of a two-center molecular continuum for gaining insights into the reaction dynamics of exotic nuclei.

    A. Gómez Camacho, A. Diaz Torres, H.Q. Zhang (2019)Comparative study of the effect of resonances of the weakly bound nuclei 6,7Li on total fusion with light to heavy mass targets, In: Physical Review C American Physical Society

    A systematic study of total fusion involving the weakly bound nuclei 6,7Li with several light to heavy mass targets at Coulomb energies is presented. Emphasis is given to the role of resonance states (l=2,Jπ=3+,2+,1+ of 6Li and l=3,Jπ=7/2−,5/2− of 7Li) on the total fusion excitation function. A comparative analysis of the effects of resonant breakup on total fusion is performed for both projectiles, using the Continuum-Discretized Coupled-Channel (CDCC) framework. The calculations demonstrate that (i) resonant breakup couplings play a more important role in total fusion than non-resonant couplings, (ii) resonance states with short half-lives are very important for total fusion, as incident energies decreases towards the Coulomb barrier energy where incomplete fusion dominates, and (iii) resonance states with long half-life act as quasi-bound inelastic states, playing a crucial role in complete fusion.

    Alexis Diaz Torres, M Wiescher (2018)Characterizing the astrophysical S-factor for 12C+12C with wave-packet dynamics, In: Physical Review C97(5)055802 American Physical Society

    A quantitative study of the astrophysically important sub-barrier fusion of 12C+12C is presented. Low-energy collisions are described in the body-fixed reference frame using wave-packet dynamics within a nuclear molecular picture. A collective Hamiltonian drives the time propagation of the wave-packet through the collective potential-energy landscape. The fusion imaginary potential for specific dinuclear configurations is crucial for understanding the appearance of resonances in the fusion cross section. The theoretical sub-barrier fusion cross sections explain some observed resonant structures in the astrophysical S-factor. These cross sections monotonically decline towards stellar energies. The structures in the data that are not explained are possibly due to cluster effects in the nuclear molecule, which are to be included in the present approach.