Coulomb Breakup Research Articles

Strong Electron-Electron-Nuclei Correlations in Two-Photon Double Ionization of H_{2}.

Two-photon double ionization is a paradigmatic example of how electron correlation manifests. In molecular targets, its coupling with the slower nuclear motion introduces an additional complication and induces electron-electron-nuclei correlations. Experimentally, momentum-coincident measurements can provide a complete kinematical image of the molecular full Coulomb breakup. Previous theoretical studies have described this process by ignoring nuclear motion and the subsequent Coulomb explosion of the dication. Here we show, by means of a full-dimensional treatment of two-photon double ionization of the H_{2} molecule, that nuclear motion plays a decisive role even for pulses as short as 1.5fs, a time during which the nuclei are not expected to move significantly. We find strong correlations between nuclear and electronic degrees of freedom, giving access to different electronic processes as a function of nuclear kinetic energy. In particular, we observe unexpectedly strong back-to-back asymmetry in the photoelectron angular distributions, as well as novel interferences resulting from the coherent contributions from two-photon sequential absorption paths via different molecular cationic states.

Breakup dynamics of a neutron-halo projectile on heavy target at deep sub-barrier energies

By studying the total fusion and breakup cross-sections in the interaction of the neutron-halo 11Be projectile on the lead target 208Pb, it is shown that, even for the neutron-halo projectile, the breakup channel remains the most dominant reaction channel at sub-barrier energies, following a characteristic behavior that was also previously verified for the case of the proton-halo projectile 8B. This feature is found to emanate from the enhancement of the breakup cross-section, due to the continuum–continuum couplings (CCC) coming exclusively from its Coulomb component. We further speculate that the enhancement of the Coulomb breakup cross-section at sub-barrier incident energies by the CCC could be associated with the projectile breaking up on the outgoing trajectory, provided these couplings can be proven to delay the breakup process.

Simultaneous calculation of elastic scattering, fusion, and direct cross sections for reactions of weakly bound projectiles

Simultaneous analyses are performed of cross-section data for elastic scattering, fusion, Coulomb breakup, and other direct yields for the He6+Bi209 system at near Coulomb-barrier energies. The bare and dynamical polarization potentials are constructed microscopically from the structure of the colliding nuclei and they reproduce all the data well with only two adjustable parameters. This method of calculation can be successfully applied to the reactions of weakly bound and exotic projectiles with heavy targets. Published by the American Physical Society 2024

Experimental study of 6He Coulomb breakup as an indirect measurement of 4He(2n,γ)6He reaction rate for the astrophysical r-process

In this work, we report the measurement of elastic and Coulomb break-up channels in 6He+208Pb collisions at Elab = 19.3 MeV, close to the Coulomb barrier of this system ∼ 19 MeV. In the context of the astrophysical r-process, the reaction 4He(2n,γ)6He has been proposed to be a key reaction in the path of synthesizing seed nuclei for the r-process, as 12C, in an environment composed mainly of alpha particles and neutrons. Based on a theoretical approach for treating three body reactions by means of which its reaction rate can be inferred, our experimental approach aims to obtain an indirect measurement of the reaction rate of 4He(2n,γ)6He by measuring the Coulomb breakup of 6He under the intense electric field produced by a 208Pb target nucleus. The experiment was carried out at the TriSol facility operated in the Nuclear Science Laboratory of the University of Notre Dame, USA, which delivered a 6He beam together with other contaminants. Particular care must be taken for the alpha particles produced in the production reaction.

Effective field theory analysis of the Coulomb breakup of the one-neutron halo nucleus 19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{19}$$\\end{document}C

We analyse the Coulomb breakup of 19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{19}$$\\end{document}C measured at 67A MeV at RIKEN. We use the Coulomb-Corrected Eikonal (CCE) approximation to model the reaction and describe the one-neutron halo nucleus 19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{19}$$\\end{document}C within Halo Effective Field Theory (Halo EFT). At leading order we obtain a fair reproduction of the measured cross section as a function of energy and angle. The description is insensitive to the choice of optical potential, as long as it accurately represents the size of 18\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{18}$$\\end{document}C. It is also insensitive to the interior of the 19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{19}$$\\end{document}C wave function. Comparison between theory and experiment thus enables us to infer asymptotic properties of the ground state of 19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{19}$$\\end{document}C: these data put constraints on the one-neutron separation energy of this nucleus and, for a given binding energy, can be used to extract an asymptotic normalisation coefficient (ANC). These results are confirmed by CCE calculations employing next-to-leading order Halo EFT descriptions of 19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{19}$$\\end{document}C: at this order the results for the Coulomb breakup cross section are completely insensitive to the choice of the regulator. Accordingly, this reaction can be used to constrain the one-neutron separation energy and ANC of 19\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${}^{19}$$\\end{document}C.

Peripheral reactions and elastic scattering induced by strongly bound, weakly bound and exotic nuclei

A phenomenological study of peripheral reactions induced by strongly bound, weakly bound and exotic projectiles on different targets is presented. A large number of experimental elastic scattering differential cross sections at energies close to the Coulomb barrier is studied on the basis of a simple nuclear optical model potential that depends on a small number of parameters. The derived wave functions, together with the imaginary component of the optical potential, allow the analysis of the radial peripheral absorption density distributions for the different kind of projectiles. These distributions, when appropriately normalized, show a clear correlation with the type of projectile regardless of the involved target and indicate that projectiles more prone to break up show a more peripheral absorption density distribution. This manifests in their magnitude, location and width. The relationship of these variables in the strongly bound group and the weakly bound group are described with a simple exponential function, while the exotic projectiles show two distinct groups, namely the neutron-halo and the proton-halo. For the neutron-halo projectiles such as He6, Li11 and Be11 there is a notable increment of the radial peripheral absorption density peak and the total reaction cross section as the breakup separation energy decreases. The same relationship is established for the proton-halo projectiles B8 and F17 but their reduced effective dipole charge leads to a lower probability of dipole Coulomb breakup that results in a substantial reduction in the extent of their peripheral absorption.

Elastic Coulomb breakup analysis via different approaches

Elastic Coulomb breakup analysis via different approaches

Calculation of Coulomb breakup cross sections using a new Coulomb dynamical polarization potential

A new method for calculating the Coulomb breakup of unstable neutron-rich isotopes at high energies is presented. The calculations employ the eikonal approximation and use a new Coulomb dynamical polarization potential (CDPP), calculated by solving the Schr\"odinger equation for the entire motion of the exotic projectile as a two-body cluster structure using the adiabatic approximation and incorporating excitations to the continuum. Calculations for some exotic isotopes are compared with Coulomb dissociation cross section data and found to be in good agreement.

Study of bound and resonance states of 11Be in breakup reaction

We investigate the Coulomb breakup of the 11 Be halo nuclei on a lead target within non-perturbative time-dependent approach in a wide range of beam energy (5–70 MeV/nucleon) including the low-lying resonances in different partial and spin states of 11 Be. We have found considerable contribution of the low-lying resonances ( 5/2+ , 3/2− and 3/2+ ) to the breakup cross section of 11 Be. The obtained results are in good agreement with existing experimental data at 69 MeV/nucleon. The developed computational scheme opens new possibilities in investigation of Coulomb, as well as nuclear, breakup of other halo nuclei on heavy, as well as, light targets.

Fragmentation dynamics of diatomic molecules under proton impact: Kinetic energy release spectra of CO$$^{{q+}}$$ and NO$$^{{q+}}$$ (q = 2, 3) molecular ions

We report on the fragmentation dynamics of triply charged, diatomic, molecular ions of NO and CO. Dissociative fragmentation after multiple ionization of NO and CO is studied under the impact of 200 keV proton beam using recoil-ion momentum spectrometer. Kinetic Energy Release distributions (KERDs) for various fragmentation channels were obtained. We have also calculated the potential energy curves (PECs) for ground and several excited states of NO^{3+} and CO^{3+} molecular ion. The obtained KERDs are discussed in the background of the calculated PECs as well as the simple Coulomb excitation model. Coulomb breakup of the unstable precursor molecular ion shows a clear preference for the N^{2+} + O^+ (and C^{2+} + O^+) fragmentation channel.

Importance of multi-step processes in the Coulomb and nuclear breakups of 15C halo nucleus

Breakup reactions involving heavy targets are known to be dominated by the Coulomb breakup, and this is understood as due to the long-range nature of Coulomb forces and a large charge of the target nucleus. In this paper, we intended to find out whether these two factors alone can justify the large importance of the Coulomb breakup over its nuclear counterpart. To this end, we considered the [Formula: see text] breakup reaction at an incident energy of [Formula: see text]. By analyzing this reaction, it is found that the continuum–continuum couplings and higher-order multipole transitions, which are characteristic of nuclear reactions induced by loosely bound projectiles, strongly suppress the nuclear breakup cross-section and have a negligible effect on the Coulomb breakup cross-section. When these reaction dynamics are removed, the nuclear breakup cross-section becomes more important than the Coulomb breakup cross-section at large incident angles. In conclusion, these results infer that the predominance of the Coulomb breakup over the nuclear breakup in reactions involving heavy targets can be explained by three main factors: the large target charge and the long-range nature of Coulomb, as well as the prevailing reaction dynamics such as continuum–continuum couplings and higher-order multipole transitions. These results could motivate further improvements on the theoretical approaches used in pure Coulomb breakup calculations.

Comparison of Coulomb breakup effects on the elastic scattering of $$^{6}$$He and $$^{8}$$He using a Coulomb dipole polarization potential

Comparison of Coulomb breakup effects on the elastic scattering of $$^{6}$$He and $$^{8}$$He using a Coulomb dipole polarization potential

Coulomb-nuclear dynamics in the breakup of the weakly bound Li8 nucleus

A detailed study of total, Coulomb, and nuclear breakup cross sections dependence on the projectile ground-state binding energy ${\ensuremath{\varepsilon}}_{b}$ is presented by considering the $^{8}\mathrm{Li}+^{12}\mathrm{C}$ and $^{8}\mathrm{Li}+^{208}\mathrm{Pb}$ breakup reactions. To this end, apart from the experimental one-neutron separation energy of $^{8}\mathrm{Li}$ nucleus $({\ensuremath{\varepsilon}}_{b}=2.03\phantom{\rule{0.16em}{0ex}}\mathrm{MeV})$, lower values of ${\ensuremath{\varepsilon}}_{b}$ down to ${\ensuremath{\varepsilon}}_{b}=0.01\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$, are also being considered. It is shown that all breakup processes become peripheral as ${\ensuremath{\varepsilon}}_{b}\ensuremath{\rightarrow}0.01\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$, which is understood as due to the well-known large spacial extension of ground-state wave functions associated to weakly bound projectiles. The Coulomb breakup cross section is found to be more strongly dependent on ${\ensuremath{\varepsilon}}_{b}$ than the nuclear breakup cross section, such that the Coulomb breakup becomes more significant as ${\ensuremath{\varepsilon}}_{b}$ decreases, even in a naturally nuclear-dominated reaction. This is mainly due to the long-range nature of the Coulomb forces, leading to a direct dependence of the Coulomb breakup on the electromagnetic transition matrix. It is also highlighted the fact that the nuclear absorption plays a minor role for small binding when the breakup becomes more peripheral.

Investigation of low-lying resonances in breakup of halo nuclei within the time-dependent approach

We investigate the Coulomb breakup of $$^{11}$$ Be halo nuclei on a heavy target ( $$^{208}$$ Pb) from intermediate (70 MeV/nucleon) to low energies (5 MeV/nucleon) within the non-perturbative semiclassical and quantum-quasiclassical time-dependent approaches. The convergence of the computational scheme is demonstrated in this energy range including n + $$^{10}$$ Be low-lying resonances in different partial and spin states. We have found a considerable contribution of the $$5/2^{+}$$ resonance ( $$E_{r}$$ = 1.23 MeV) to the breakup cross section at 30 MeV/nucleon and lower, while at higher energies, the resonant states $$3/2^{-}$$ and $$3/2^{+}$$ (with $$E_{r}$$ = 2.78 and 3.3 MeV) make most visible contributions. The obtained results are in good agreement with experimental data available at 69 and 72 MeV/nucleon. Comparison with the existing theoretical calculations of other authors for 20 and 30 MeV/nucleon is also made. The developed computational scheme opens new possibilities in the investigation of the Coulomb, as well as nuclear, breakup of other halo nuclei on heavy and light targets.

Coulomb and nuclear interactions in the dynamics of weakly-bound neutron-halo breakup on heavy target * *LT acknowledge support from Conselho Nacional de Desenvolvimento Científico e Tecnológico [Procs. 304469-2019-0 and 464898/2014-5 (INCT-FNA)], and Fundação de Amparo à Pesquisa do Estado de São Paulo [Projs. 2017/05660-0]

Within our aim to clarify some aspects of the breakup dynamics of loosely-bound neutron-halo projectiles on a heavy target, we apply the continuum discretized coupled-channel formalism to investigate the beryllium 11Be breakup on a lead 208Pb target at = 140 MeV incident energy. By evidencing that the continuum–continuum couplings are much stronger in the nuclear breakup than in the Coulomb breakup, we conclude that the strength of these couplings in the total breakup is dominated by the nuclear contribution, with the diagonal monopole nuclear potential in the projectile–target center-of-mass having negligible effect on the total and nuclear breakup cross-sections. For this kind of reaction, we show that the condition for the total breakup to approach its dominant component in the absorption region is strongly dependent on the continuum–continuum couplings and the diagonal monopole nuclear potential.

Systematic study on the role of various higher-order processes in the breakup of weakly-bound projectiles

Abstract The virtual photon theory (VPT), which is based on first-order Coulomb dissociation restricted to the electric dipole (E1), has been successfully used to explain the breakup data for several cases. Our aim is to study the role of various higher-order processes that are ignored in the VPT, such as the nuclear breakup, interference between nuclear and Coulomb amplitudes, and multistep breakup processes mainly due to strong continuum-continuum couplings in the breakup of two-body projectiles on a heavy target at both intermediate and higher incident energies. For the purpose of numerical calculations, we employed eikonal version of three-body continuum-discretized coupled-channels (CDCC) reaction model. Our results for the breakup of 11Be and 17F on 208Pb target at 100, 250, and 520 MeV/A, show the importance of nuclear breakup contribution, and its significant role in the multistep processes. The multistep effect on Coulomb breakup for core-neutron projectile was found to be negligible, whereas it was important for core-proton projectile. Coulomb-nuclear interference (CNI) effect was also found to be non-negligible. Qantitatively, the multistep effects due to the nuclear breakup was found to depend on the incident energy through the energy dependence of the core-target and nucleon-target nuclear potentials. The nuclear breakup component, the CNI effect, and the multistep breakup processes are all found to be non-negligible; hence, the assumptions adopted in the VPT for the accurate description of breakup cross sections are not valid.

Exploring the structure of 29Ne

We apply a fully quantum mechanical Coulomb breakup theory under the aegis of post form finite-range distorted wave Born approximation to analyze the elastic Coulomb breakup of 29Ne on 208Pb at 244MeV/u. We calculate several reaction observables to quantify its structural parameters. One-neutron removal cross section is calculated to check the consistency of the ground state configuration of 29Ne with the available experimental data. A scrutiny of the parallel momentum distribution of the charged fragment reveals a full width at half maximum of 82MeV/c, which is in good agreement with the experimental value and indicates a moderate halo for a nearly spherical 29Ne in the 28Ne(0+)⊗2p3/2ν ground state. The energy-angular distributions and average momentum of the charged fragment point to the absence of post-acceleration effects in the breakup process, a desirable result for elastic breakup.

Proton-halo breakup dynamics for the breakup threshold in the ε 0 → 0 limit

Proton-halo breakup behavior in the limit (where is the ground-state binding energy) is studied around the Coulomb barrier in the reaction for the first time. For practical purposes, apart from the experimental binding energy of 137 keV, three more arbitrarily chosen values (1, 0.1, 0.01 keV) are considered. It is first shown that the Coulomb barrier between the core and the proton prevents the system from reaching the state of an open proton-halo system, which, among other factors, would require the ground-state wave function to extend to infinity in the asymptotic region, as . The elastic scattering cross section, which depends on the density of the ground-state wave function, is found to have a negligible dependence on the binding energy in this limit. The total, Coulomb and nuclear breakup cross sections are all reported to increase significantly from to 1.0 keV, and converge to their maximum values as . This increase is mainly understood as coming from a longer tail of the ground-state wave function for keV, compared to that for keV. It is also found that the effect of the continuum-continuum couplings is to slightly delay the convergence of the breakup cross section. The analysis of the reaction cross section indicates a convergence of all the breakup observables as . These results provide a better sense of the dependence of the breakup process on the breakup threshold.

Three-body breakup of 6He and its halo structure

The Borromean halo nucleus 6He has been studied by a kinematically complete measurement of Coulomb and nuclear breakup into α + 2n on Pb and C targets at 70 MeV/nucleon. Fully quantum-mechanical four-body breakup calculations reproduce the energy and angular differential cross sections below Erel∼1 MeV for both targets. The model used here reproduces the 6He ground-state properties as well as α-n and n-n scattering data and predicts an average opening angle 〈θnn〉 of 68∘ between the two halo neutrons. However, the model underestimates the breakup cross sections for higher Erel, indicating a possible contribution from the inelastic breakup. Alternatively, we examine the empirically modified calculations that reproduce the energy-differential cross sections for a wide range of scattering angles for both targets. The extracted B(E1) peaks at Erel∼1.4 MeV and amounts to 1.6(2) e2fm2 for Erel ≤ 20 MeV, resulting 〈θnn〉 = 56−10+9 degrees. In either interpretation, the current results show evidence of the dineutron spatial correlation in 6He.

Comparative analysis of s-wave and p-wave breakups in 37Mg +208Pb reaction

A comparative study of [Formula: see text]-wave and [Formula: see text]-wave breakups in the [Formula: see text] reaction around the Coulomb barrier is presented. The elastic scattering, breakup and reaction cross-sections, corresponding to the three [Formula: see text], [Formula: see text] and [Formula: see text] possible single-particle configurations in the [Formula: see text] ground state, calculated with two different [Formula: see text] ground-state binding energies, namely 0.22 and 0.49[Formula: see text]MeV are analyzed. As in the breakup of other neutron-halo systems such as [Formula: see text], it is found that for all three ground-state configurations, couplings to the breakup channels suppress the Coulomb–nuclear interference peak in the elastic scattering cross-section. It is shown that the breakup through [Formula: see text]-wave ground state is dominated by couplings to continuum [Formula: see text]-waves, whereas the breakup through [Formula: see text]-wave ground state, is largely dominated by couplings to continuum [Formula: see text]-wave. Substantially larger [Formula: see text] ground state total, Coulomb and nuclear breakup cross-sections than their [Formula: see text] and [Formula: see text] ground states counterparts are obtained. This is understood to mainly originate from a larger electric dipole response function of the transition from [Formula: see text] ground state to the continuum, and from the fact that the Coulomb breakup cross-section is directly proportional to this function. In conclusion, the breakup of [Formula: see text] nucleus exhibits a similar breakup behavior as other one-neutron loosely bound systems. The results presented in this paper may provide some guidance for experimentalists to analyze possible future experimental data.