Heavy-ion Reactions Research Articles

Reconstruction of Bremsstrahlung γ-rays spectrum in heavy ion reactions with Richardson-Lucy algorithm

The high momentum tail (HMT) in the momentum distribution of nucleons above the Fermi surface has been regarded as an evidence of short-range correlations (SRCs) in atomic nuclei. It has been showcased recently that the np Bremsstrahlung radiation in heavy ion reactions can be used to extract HMT information. The Richardson-Lucy (RL) algorithm is introduced to the reconstruction of the original Bremsstrahlung γ-ray energy spectrum from experimental measurements. By solving the inverse problem of the detector response to the γ-rays, the original energy spectrum of the Bremsstrahlung γ in 25 MeV/u 86Kr + 124Sn has been reconstructed and compared to the isospin- and momentum-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) simulations. The analysis based on hypothesis test suggests the existence of the HMT of nucleons in nuclei, in accordance with the previous conclusions. With its effectiveness being demonstrated, it is feasible to apply the RL algorithm in future experiments of measuring the Bremsstrahlung γ-rays in heavy ion reactions.

Medically relevant radioisotope production through low energy heavy ion reactions

Medically relevant radioisotope production through low energy heavy ion reactions

The slopes of sub-barrier heavy-ion fusion excitation functions shed light on the dynamics of quantum tunnelling

Quantum tunnelling plays a crucial role in heavy-ion fusion reactions at sub-barrier energies, especially in the context of nuclear physics and astrophysics. The nuclear structure of the colliding nuclei and nucleon transfer processes represent intrinsic degrees of freedom. They are coupled to the relative ion motion and, in general, increase the probability of tunnelling. The influence of couplings to nucleon transfer channels relatively to inelastic excitations, on heavy-ion fusion cross sections, is one of the still open problems in this field. We present a new analysis of several systems, based on the combined observation of the energy-weighted excitation functions Eσ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\sigma $$\\end{document} in relation to their first energy derivatives d(Eσ)/dE\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d(E\\sigma )/dE$$\\end{document}. The relation between d(Eσ)/dE\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$d(E\\sigma )/dE$$\\end{document} and Eσ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$E\\sigma $$\\end{document} removes the basic differences due to the varying Coulomb barrier when comparing different systems. We show that, depending on the nuclear structure and/or the presence of strong transfer channels, this representation reveals characteristic features below the barrier. The possible presence of cross section oscillations makes this analysis less clear for light- or medium-light systems.

NeuSIM4: A comprehensive GEANT4 based neutron simulation code

A new neutron SIMulation program based on the versatile GEANT4 toolkit, neuSIM4, has been developed to describe interactions of neutrons in the NE213 liquid scintillator from 0.1 to 3000 MeV. neuSIM4 is designed to accommodate complicated modern detector geometry setups with multiple scintillator detectors, each of which can be outfitted with more than one photo-multiplier. To address a broad spectrum of neutron energies, two new neutron interaction physics models, KSCIN and NxQMD, have been implemented in GEANT4. For neutrons with energy below 110 MeV, we incorporate a total of eleven neutron induced reaction channels on hydrogen and carbon nuclei, including nine carbon inelastic reaction channels, into KSCIN. Beyond 110 MeV, we implement a neutron induced reaction model, NxQMD, in GEANT4. We use its results as reference to evaluate other neutron-interaction physics models in GEANT4. We find that results from an existing cascade physics model (INCL) in GEANT4 agree very well with the results from NxQMD, and results from both codes agree with new and existing light response data. To connect KSCIN to NxQMD or INCL, we introduce a transition region where the contribution of neuSIM4 linearly decreases with corresponding increased contributions from NxQMD or INCL. To demonstrate the application of the new code, we simulate the light response and performance of a 2 × 2 m2 neutron detector wall array consisting of 25 2m-long scintillation bars. We are able to compare the predicted light response functions to the shape of the experimental response functions and calculate the efficiency of the neutron detector array for neutron energies up to 200 MeV. These simulation results will be pivotal for understanding the performance of modern neutron arrays with intricate geometries, especially in the measurements of neutron energy spectra in heavy-ion reactions.

Quantum mechanical treatment of nuclear friction in coupled-channels heavy-ion fusion

Nuclear friction causes energy dissipation in heavy-ion collisions. Its understanding and inclusion in quantum mechanical reaction models are crucial for advancing the physics of heavy-ion reactions forming heavy elements. The effects of nuclear friction on heavy-ion fusion reactions are investigated using the coupled-channels density-matrix method. In this open-quantum-system description, a phenomenological nuclear friction form factor is introduced along with coherent coupled-channels effects. The key nucleus was the 92Zr target, due to its high density of low-lying non-collective excited states, which was recently theorised to be cause of nuclear friction. The calculations using the 16O + 92Zr collision showed that the inclusion of nuclear friction effects increased the fusion probability significantly, and that the agreement between the theoretical and experimental fusion barrier distributions was improved when nuclear friction effects were included.

Exploring fission and quasi-fission in 31Al + 197Au: probing energies near and beyond Coulomb barrier

An idea to understand the fragmentation of a formed nuclear entity (i.e. compound nucleus), induced via heavy-ion reactions, is an interesting task especially at incident energies near, above and far away from the Coulomb barrier. In the present work, we are studying the decay dynamics of a formed nuclear entity i.e. 228U* compound nucleus (CN), via the radioactive beam of Aluminium-31 (31Al) striking on the stable Gold-197 (197Au) target nucleus, for incident energies E c.m. = 106.2–163.2 MeV. A comprehensive knowledge regarding the probable decaying fragments from 228U* has been accumulated using the collective clusterization approach of the Dynamical Cluster-decay Model (DCM) in terms of mass and charge dispersion, which built up on the Quantum Mechanical Fragmentation Theory (QMFT). Through both of these dispersion cases, we have identified the decaying fragments in the fission and heavy-mass regions, at different scale of incident energies. Further, the fission cross-sections ( σfisTheo ) have been obtained for 31Al + 197Au → 228U* reaction at the above said E c.m. (MeV) and compared with the experimental data. This study has been carried out using two different sets of Skyrme force parameters (SIII and SSk), which are employed within the semiclassical approach of Skyrme Energy Density Formalism. Unlike for energies below and near the barrier, a significant difference has been observed between calculated ( σfisTheo ) and experimental ( σfisExpt ) cross-sections for above barrier energies, with independent choice of Skyrme forces. Such discrepancy noticed has been addressed with the presence of quasi-fission (QF) event. Similar phenomena has also been seen for 19F-induced reaction forming the same CN (228U*).

Microscopic study of deformation and orientation effects in heavy-ion reactions above the Coulomb barrier using the Boltzmann-Uehling-Uhlenbeck model

Microscopic study of deformation and orientation effects in heavy-ion reactions above the Coulomb barrier using the Boltzmann-Uehling-Uhlenbeck model

Development of a low-pressure Multi-Mesh THGEM detector for fission experiments at FRIB

A small-area imaging detector prototype for position measurement of fission fragments produced in low energy heavy-ion reactions is presented in this study. The detector readout is equipped with a 2-dimensional, position-sensitive gaseous avalanche readout based on the novel Multi-Mesh Thick-GEM (MM-THGEM), and is coupled to a delay-line board for particle localization. The prototype has an effective area of 10 × 10 cm2 and is operated in isobutane at low pressure (7–10 Torr). We present and discuss a series of systematic evaluation tests performed by irradiating the detector with α-particles and fission fragments emitted by small-rate sources (241Am, 249Cf and 252Cf). Position and time resolutions of about 0.42 mm and 1 ns were achieved, respectively. This work serves as a benchmark for the development of a large-scale array of detectors for experiments with fission and fission-like reaction products at the Facility for Rare Isotope Beams (FRIB).

Search for beyond-mean-field signatures in heavy-ion fusion reactions

Search for beyond-mean-field signatures in heavy-ion fusion reactions

Transfer learning and neural networks in predicting quadrupole deformation

Abstract Accurately determining the quadrupole deformation parameters of atomic nuclei is crucial for understanding their structural and dynamical properties. This study introduces an innovative approach that combines transfer learning techniques with neural networks to predict the quadrupole deformation parameters of even-even nuclei. With the application of this innovative technique, the quadrupole deformation parameters of 2331 even-even nuclei are successfully predicted within the nuclear region defined by proton numbers \(8 \leq Z \leq 134\) and neutron numbers \(N \geq 8\). Additionally, the study discusses the impact of nuclear quadrupole deformation parameters on the capture cross-sections in heavy-ion fusion reactions, reconstructing the capture cross-sections for the reactions \(^{48}\text{Ca} + ^{244}\text{Pu}\) and \(^{48}\text{Ca} + ^{248}\text{Cm}\). This research offers new insights into the application of neural networks in nuclear physics and underscores the potential of merging advanced machine learning techniques with both theoretical and experimental data, particularly in fields where experimental data is limited.

A study the 16 O + 166 E R , 16 O + 197 Au Systems Using Calculations of Quasi-elastic Scattering

Specific systematic studies on the nuclear potential parameter for the heavy-ion reactions which includes the systems have been achieved by using large-angle quasi elastic scattering at deep sub-barrier energies close to the Coulomb barrier height. The elastic scattering barrier distribution Dqelas a function of energy has also been calculated in this theoretical study. The single-channel (SC) and coupled-channels calculations have been carried out to elicit the nuclear potential. The chi-square method X2 has been used find the best value of the nuclear potential in comparison with the experimental data. The best values of the nuclear potential were found from the calculations of the single channels for systems: 16O+166ER , 16O+197Au, which are equal to (60.5, 100) MeV, respectively.

Probing high-momentum component in nucleon momentum distribution by neutron-proton bremsstrahlung γ-rays in heavy ion reactions

The high momentum tail (HMT) of nucleons, as a signature of the short-range correlations in nuclei, has been investigated by the high-energy bremsstrahlung γ rays produced in 86Kr+124Sn at 25 MeV/nucleon. The energetic photons are measured by a CsI(Tl) hodoscope mounted on the spectrometer CSHINE. The energy spectrum ≥35 MeV can be reproduced by the Isospin- and Momentum-Dependent Boltzmann-Uehling-Uhlenbeck model calculations incorporating the photon production channel from np process in which the HMTs of nucleons is considered. A non-zero HMT ratio of about 15% is favored by the data. The effect of the capture channel np→dγ is demonstrated.

Measurement of the high energy γ-rays from heavy ion reactions using Čerenkov detector

Measurement of the high energy γ-rays from heavy ion reactions using Čerenkov detector

The 50th anniversary of the coupled channels Born approximation (CCBA) and the coupled reaction channels (CRC) theories of nucleon transfer reactions (a unique interplay between theory, experiment and computer technology, conducted during the most tumultuous period in modern American society)

Nucleon transfer reactions have played a fundamental role in understanding the single-particle components, shell structure and collective properties of atomic nuclei. The conventional distorted wave Born approximation (DWBA) envisioned the nucleon transfer reaction as a one-step process, which proceeds directly from the ground state of the target nucleus to a state of the residual nucleus. The coupled channels Born approximation (CCBA) and coupled reaction channels (CRC) theories evolved because a number of nucleon transfer reaction cross sections could not be reconciled within the DWBA. These coupled channels models revealed that, in addition to the “one-step” process of the DWBA, “multi-step” nucleon transfer processes involving accessary pathways can participate in populating the final nuclear state. In the CCBA, the auxiliary pathways involved inelastic excitations of the target and/or residual nucleus, whereas, in the CRC, the pathways included sequential nucleon transfer passing through nuclear states of an intermediate partition. Coherent addition of contributions from one-step and multi-step nucleon transfer processes resulted in dramatic alterations in reaction cross sections, which were experimentally confirmed. The CCBA and CRC linked the structure of the nuclei participating in a reaction to modalities of nucleon transfer arising during the relative motion between the interacting ions. These complementary theories inexorably changed physicists’ interpretations of nucleon transfer reactions and, in doing so, heralded in the new field of direct heavy-ion reactions.

Application of a universal reaction function to the description of heavy-ion reaction cross sections

Application of a universal reaction function to the description of heavy-ion reaction cross sections

Modeling Double Charge Exchange processes occurring in Heavy Ion Reactions

Heavy ion induced double charge exchange reactions are treated as an incoherent sequence of two reactions driven by the exchange of charged mesons (double single charge exchange, DSCE). The process is described within a fully quantum mechanical distorted wave 2-step theory (2nd order DWBA). The DSCE reaction amplitudes are shown to be separable into superpositions of distortion factors, accounting for initial and final state ion-ion elastic interactions, and nuclear matrix elements (NMEs). Explicit expressions of projectile and target NMEs are derived within the QRPA theory. Reduction schemes for the DSCE transition form factors are described, analizing their momentum structure within the closure approximation. Formal analogies between the NMEs involved in DSCE reactions and in double beta decays are also pointed out. Results, obtained within this theoretical framework, are illustrated for the reaction 40Ca (18O, 18Ne)40Ar at 15.3 AMeV and compared to the data measured at INFN-LNS by the NUMEN Collaboration. Furthermore, preliminary results for reactions involving heavier systems, such as 76Se (18O, 18Ne)76Ge, are shown.

Generation of fusion and fusion-evaporation reaction cross-sections by two-step machine learning methods

In order to obtain cross-sections of heavy-ion fusion and fusion-evaporation reactions, artificial neural networks, cubist, random forest, support vector regression, extreme gradient boosting, and multiple linear regression machine learning approaches were used separately in this study. The outcomes from these different methods that are obtained from the training carried out with the existing experimental data in the literature were compared. Furthermore, it has been observed that a two-step process yielded better results for determining the heavy-ion reaction cross-sections, after first estimating which approach would be better for which reaction. In this manner, the method for which the cross-section needs to be calculated is determined by the machine learning classification application, and predictions can be made using the machine learning regression application with the determined method. It has been concluded that the obtained results are in harmony with the experimental data and that the methods can be used safely. The obtained results are published on a web page that allows for online calculation of heavy-ion fusion and fusion-evaporation reaction cross-sections.

Fabrication and characterization of thin [formula omitted]Sn films for heavy-ion nuclear reaction measurements

The fabrication of thin isotopically enriched 120,124Sn targets have been presented. The thin film targets prepared have been used in nuclear physics experiments to apprehend the heavy-ion fusion and multi-nucleon transfer reaction dynamics around the Coulomb barrier. Vacuum evaporation viz. resistive heating technique has been used for the fabrication of the targets with varying areal densities in the range of 50–250 μg/cm2 backed with a carbon layer of ≈20μg/cm2 using a nominal amount of 30 mg isotopically enriched material. The fabricated targets have been characterized using multiple advanced techniques viz. Energy Dispersive X-ray Spectroscopy (EDS), Scanning Electron Microscopy (SEM), and X-ray Diffractometry (XRD). The thickness of the targets has been measured using Rutherford Back-scattering Spectrometry (RBS). The isotopic contamination levels have been ascertained with an in-beam experiment using Heavy Ion Reaction Analyzer at IUAC, New Delhi.

Semirelativistic antisymmetrized molecular dynamics for the production of energetic neutrons in intermediate-energy heavy-ion reactions

Semirelativistic antisymmetrized molecular dynamics for the production of energetic neutrons in intermediate-energy heavy-ion reactions

Global angular momentum generation in heavy-ion reactions within a hadronic transport approach

Global angular momentum generation in heavy-ion reactions within a hadronic transport approach