# Dr Alexis Diaz-Torres

Senior Lecturer 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

Department of Physics.

### Areas of specialism

Theoretical Nuclear Physics; Nuclear Structure and Reactions; 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)

### 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

Diaz-Torres A (2008) Solving the two-center nuclear shell-model problem with arbitrarily oriented deformed potentials, PHYSICAL REVIEW LETTERS 101 (12) ARTN 122501 AMER PHYSICAL SOC
Rafiei R, du Rietz R, Luong DH, Hinde DJ, Dasgupta M, Evers M, Diaz-Torres A (2010) Mechanisms and systematics of breakup in reactions of Be-9 at near-barrier energies, PHYSICAL REVIEW C 81 (2) ARTN 024601 AMER PHYSICAL SOC
Diaz-Torres A (2010) Coupled-channels density-matrix approach to low-energy nuclear collision dynamics: A technique for quantifying quantum decoherence effects on reaction observables, PHYSICAL REVIEW C 82 (5) ARTN 054617 AMER PHYSICAL SOC
Souza FA, Carlin N, Beck C, Keeley N, Diaz-Torres A, Liguori Neto R, Siqueira-Mello C, de Moura MM, Munhoz MG, Oliveira RAN, Del Santo MG, Suaide AAP, Szanto EM, de Toledo AS (2010) Projectile breakup dynamics for Li-6+Co-59: Kinematical analysis of alpha-d coincidences, EUROPEAN PHYSICAL JOURNAL A 44 (2) pp. 181-187 SPRINGER
Diaz-Torres A (2011) PLATYPUS: A code for reaction dynamics of weakly-bound nuclei at near-barrier energies within a classical dynamical model, COMPUTER PHYSICS COMMUNICATIONS 182 (4) pp. 1100-1104 ELSEVIER SCIENCE BV
Thomas RG, Hinde DJ, Duniec D, Zenke F, Dasgupta M, Brown ML, Evers M, Gasques LR, Rodriguez MD, Diaz-Torres A (2008) Entrance channel dependence of quasifission in reactions forming Th-220, PHYSICAL REVIEW C 77 (3) ARTN 034610 AMER PHYSICAL SOC
Hinde DJ, Dasgupta M, Diaz-Torres A, Evers M (2010) Quantum coherence and decoherence in low energy nuclear collisions: from superposition to irreversibility, NUCLEAR PHYSICS A 834 (1-4) pp. 117C-122C ELSEVIER SCIENCE BV
Dasgupta M, Hinde DJ, Diaz-Torres A, Bouriquet B, Low CI, Milburn GJ, Newton JO (2007) Beyond the coherent coupled channels description of nuclear fusion, PHYSICAL REVIEW LETTERS 99 (19) ARTN 192701 AMER PHYSICAL SOC
Gasques LR, Dasgupta M, Hinde DJ, Peatey T, Diaz-Torres A, Newton JO (2006) Isomer ratio measurements as a probe of the dynamics of breakup and incomplete fusion, PHYSICAL REVIEW C 74 (6) ARTN 064615 AMERICAN PHYSICAL SOC
Dasgupta M, Gasques LR, Luong DH, du Rietz R, Rafiei R, Hinde DJ, Lin CJ, Evers M, Diaz-Torres A (2010) Reaction dynamics of weakly bound nuclei at near-barrier energies, NUCLEAR PHYSICS A 834 (1-4) pp. 147C-150C ELSEVIER SCIENCE BV
Luong DH, Dasgupta M, Hinde DJ, du Rietz R, Rafiei R, Lin CJ, Evers M, Diaz-Torres A (2011) Insights into the mechanisms and time-scales of breakup of Li-6,Li-7, PHYSICS LETTERS B 695 (1-4) pp. 105-109 ELSEVIER SCIENCE BV
Diaz-Torres A, Hinde DJ, Tostevin JA, Dasgupta M, Gasques LR (2007) Relating breakup and incomplete fusion of weakly bound nuclei through a classical trajectory model with stochastic breakup, PHYSICAL REVIEW LETTERS 98 (15) ARTN 152701 AMERICAN PHYSICAL SOC
Diaz-Torres A, Gasques LR, Wiescher M (2007) Effects of nuclear molecular configurations on the astrophysical S-factor for O-16+O-16, PHYSICS LETTERS B 652 (5-6) pp. 255-258 ELSEVIER SCIENCE BV
Diaz-Torres A (2010) Absence of decoherence in the complex-potential approach to nuclear scattering, PHYSICAL REVIEW C 81 (4) ARTN 041603 AMER PHYSICAL SOC
Diaz-Torres A, Hinde DJ, Dasgupta M, Milburn GJ, Tostevin JA (2009) Coupled-Channels Approach for Dissipative Quantum Dynamics in Near-Barrier Collisions, FUSION 08 1098 pp. 44-51 AMER INST PHYSICS
Diaz-Torres A (2006) Dynamical collective potential energy landscape: Its impact on the competition between fusion and quasi-fission in a heavy fusing system, FUSION06: Reaction Mechanisms and Nuclear Structure at the Coulomb Barrier 853 pp. 225-230 AMER INST PHYSICS
Beck C, Keeley N, Diaz-Torres A (2007) Coupled-channel effects in elastic scattering and near-barrier fusion induced by weakly bound nuclei and exotic halo nuclei, PHYSICAL REVIEW C 75 (5) ARTN 054605 AMERICAN PHYSICAL SOC
Beck C, Keeley N, Diaz-Torres A (2008) Cluster model for near-barrier fusion induced by weakly bound and halo nuclei, FRONTIERS IN NUCLEAR STRUCTURE, ASTROPHYSICS, AND REACTIONS 1012 pp. 233-237 AMER INST PHYSICS
Diaz Torres A, Moro AM (2014) Insights into low-energy elastic scattering of halo nuclei, Physics Letters B 733 pp. 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.
Dasgupta M, Hinde DJ, Diaz-Torres A, Luong DH (2009) Towards a Consistent Understanding of Near-barrier Reactions, FUSION 08 1098 pp. 11-17 AMER INST PHYSICS
Diaz Torres A, Adamian GG, Sargsyan VV, Antonenko NV (2014) Energy-shifting formulae yield reliable reaction and capture probabilities, Physics Letters B 739 pp. 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.
Beck C, Rowley N, Papka P, Courtin S, Rousseau M, Souza FA, Carlin N, Liguori Neto F, De Moura MM, Del Santo MG, Suade AAI, Munhoz MG, Szanto EM, De Toledo AS, Keeley N, Diaz-Torres A, Hagino K (2011) CLUSTER MODEL FOR REACTIONS INDUCED BY WEAKLY BOUND AND/OR EXOTIC HALO NUCLEI WITH MEDIUM-MASS TARGETS, INTERNATIONAL JOURNAL OF MODERN PHYSICS E-NUCLEAR PHYSICS 20 (4) pp. 943-946 WORLD SCIENTIFIC PUBL CO PTE LTD
Diaz-Torres A, Hinde DJ, Dasgupta M, Milburn GJ, Tostevin JA (2008) Dissipative quantum dynamics in low-energy collisions of complex nuclei, PHYSICAL REVIEW C 78 (6) ARTN 064604 AMER PHYSICAL SOC
Diaz-Torres A, Gasques LR, Wiescher M (2008) ASTROPHYSICAL S-FACTOR FOR O-16+O-16 WITHIN THE ADIABATIC MOLECULAR PICTURE, INTERNATIONAL JOURNAL OF MODERN PHYSICS E-NUCLEAR PHYSICS 17 (10) pp. 2194-2198 WORLD SCIENTIFIC PUBL CO PTE LTD
Diaz-Torres A (2006) Competition between fusion and quasifission in a heavy fusing system: Diffusion of nuclear shapes through a dynamical collective potential energy landscape, PHYSICAL REVIEW C 74 (6) ARTN 064601 AMERICAN PHYSICAL SOC
Souza FA, Carlin N, Beck C, Keeley N, Diaz-Torres A, Liguori Neto R, Siqueira-Mello C, de Moura MM, Munhoz MG, Oliveira RAN, Del Santo MG, Suaide AAP, Szanto EM, de Toledo AS (2010) Li-6 direct breakup lifetimes, NUCLEAR PHYSICS A 834 (1-4) pp. 420C-423C ELSEVIER SCIENCE BV
Beck C, Zafra ASI, Diaz-Torres A, Thompson IJ, Keeley N, Souza FA (2006) Near-barrier fusion induced by stable weakly bound and exotic halo light nuclei, FUSION06: REACTION MECHANISMS AND NUCLEAR STRUCTURE AT THE COULOMB BARRIER 853 pp. 384-389 AMER INST PHYSICS
Hinde DJ, Thomas RG, du Rietz R, Diaz-Torres A, Dasgupta M, Brown ML, Evers M, Gasques LR, Rafiei R, Rodriguez MD (2008) Disentangling effects of nuclear structure in heavy element formation, PHYSICAL REVIEW LETTERS 100 (20) ARTN 202701 AMER PHYSICAL SOC
Beck C, Rowley N, Papka P, Courtin S, Rousseau M, Souza FA, Carlin N, Liguori Neto R, de Moura MM, Del Santo MG, Suaide AAP, Munhoz MG, Szanto EM, de Toledo AS, Keeley N, Diaz-Torres A, Hagino K (2010) Reaction mechanisms for weakly-bound, stable nuclei and unstable, halo nuclei on medium-mass targets, NUCLEAR PHYSICS A 834 (1-4) pp. 440C-445C ELSEVIER SCIENCE BV
Diaz-Torres A (2010) Modelling incomplete fusion dynamics of weakly bound nuclei at near-barrier energies, JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 37 (7) ARTN 075109 IOP PUBLISHING LTD
Hinde DJ, du Rietz R, Thomas RG, Rafiei R, Dasgupta A, Diaz-Torres A (2009) Fission and quasi-fission: insights into heavy element formation reactions, FUSION 08 1098 pp. 281-288 AMER INST PHYSICS
Diaz Torres A (2017) Molecular Structure in Slow Nuclear Collisions, In: Wolf-Udo S (eds.), Nuclear Particle Correlations and Cluster Physics pp. 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.
Diaz Torres Alexis (2017) OWL: a code for the two-center shell model with spherical Woods-Saxon potentials, Computer Physics Communications 224 pp. 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.
Diaz Torres Alexis, Quraishi Daanish (2018) Effects of unconventional breakup modes on incomplete fusion of weakly bound nuclei, Physical Review C 97 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.
Diaz Torres Alexis, Wiescher M (2018) Characterizing the astrophysical S-factor for 12C+12C with
wave-packet dynamics,
Physical Review C 97 (5) 055802 pp. 055802-1 - 055802-8 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.
Diaz-Torres A, Hinde D J, Tostevin J A, Dasgupta M, Gasques L R (2007) Relating Breakup and Incomplete Fusion of Weakly Bound Nuclei Through a Classical Trajectory Model with Stochastic Breakup, Physical Review Letters 98 (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.

Diaz-Torres A., Hinde D. J., Tostevin J. A., Dasgupta M., Gasques L. R. (2007) Relating Breakup and Incomplete Fusion of Weakly Bound Nuclei through a Classical Trajectory Model with Stochastic Breakup, Physical Review Letters 98 (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.

Gómez Camacho A., Diaz Torres A., Zhang H.Q. (2019) Comparative study of the effect of resonances of the weakly bound nuclei 6,7Li on total fusion with light to heavy mass targets, 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,JÀ=3+,2+,1+ of 6Li and l=3,JÀ=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.
Diaz-Torres Alexis, Wiescher Michael (2019) Resonances in Stellar Carbon Fusion, Springer Proceedings in Physics - Nuclei in the Cosmos XV 219 pp. 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.
Li G. S., Fang Y. D., Diaz-Torres A., Liu M. L., Zhang N. T., Zhou X. H., Zhang Y. H., Wang J. G., Gao B. S., Qiang Y. H., Guo S., Wang S. C., Zhang Z. Y., Huang J. F., Wang K. L., Zheng Y., Mukherjee S. (2019) Isomer yield ratios in 184Re from the 9Be + 181Ta reaction, Physical Review C 99 (5) 054617 pp. 054617-1 - 054617-6 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 ³-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.
Vockerodt Terry, Diaz-Torres Alexis (2019) Describing heavy-ion fusion with quantum coupled-channels wave-packet dynamics, Physical Review C 100 034606 pp. 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.
Van den Bossche Rafael, Diaz-Torres Alexis (2019) Modelling incomplete fusion dynamics of complex nuclei at Coulomb energies, Physical Review C 100 (4) 044604 pp. 044604-1 American Physical Society
The incomplete fusion dynamics of ²pNe + ²pxPb 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.
Lee Iain, Diaz-Torres Alexis (2019) Populating high spin states of a compound nucleus with the incomplete fusion mechanism: the effectiveness of heavy projectiles, 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.
Li G.S, Liu M.L, Patel D., Fang Y.D, Zhou X.H, Zhang Y.H, Diaz Torres Alexis, Palshetkar C.S, Lubian J., Zhang N.T, Wang J.G, Gao B.S, Qiang Y.H, Guo S., Zheng Y., Wang K.L, Zheng K.K, Li R, Mukherjee S. (2020) Fusion reaction studies for the 9Be + 89Y system at above-barrier energies, 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 ³ -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.
Adamian G.G, Antonenko N.V, Diaz Torres Alexis, Heinz S. (2020) How to extend the chart of nuclides?, EUROPEAN PHYSICAL JOURNAL A 56 (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.