Giant Resonance Research Articles

Isoscalar monopole and quadrupole modes in Mo isotopes: Microscopic analysis

The recent RCNP (α,α′) data on the Isoscalar Giant Monopole Resonance (ISGMR) and Isoscalar Giant Quadrupole Resonance (ISGQR) in 92,94,96,98,100Mo are analyzed within a fully self-consistent Quasiparticle Random Phase Approximation (QRPA) approach with Skyrme interactions, in which pairing correlations and possible axial deformations are taken into account. The Skyrme sets SkM*, SLy6, SVbas and SkPδ, that explore a diversity of nuclear matter properties, are used. We discuss the connection between the line shape of the monopole strength ISGMR and the deformation-induced coupling between the ISGMR and the K=0 branch of the ISGQR. The ISGMR is best described by the force SkPδ, having a low incompressibility K∞=202MeV. The ISGQR data are better reproduced by SVbas, that has large isoscalar effective mass m⁎/m=0.9. The need of a functional that can describe simultaneously the ISGMR and ISGQR data is stressed, with the requirement of suitable values of K∞ and m⁎/m. Possible extensions of the QRPA to deal with soft systems are also envisaged.

Hydrogen-Doping-Induced Metal-Like Ultrahigh Free-Carrier Concentration in Metal-Oxide Material for Giant and Tunable Plasmon Resonance.

The practical utilization of plasmon-based technology relies on the ability to find high-performance plasmonic materials other than noble metals. A key scientific challenge is to significantly increase the intrinsically low concentration of free carriers in metal-oxide materials. Here, a novel electron-proton co-doping strategy is developed to achieve uniform hydrogen doping in metal-oxide MoO3 at mild conditions, which creates a metal-like ultrahigh free-carrier concentration approaching that of noble metals (1021 cm-3 in H1.68 MoO3 versus 1022 cm-3 in Au/Ag). This bestows giant and tunable plasmonic resonances in the visible region to this originally semiconductive material. Using ultrafast spectroscopy characterizations and first-principle simulations, the formation of a quasi-metallic energy band structure that leads to long-lived and strong plasmonic field is revealed. As verified by the surface-enhanced Raman spectra (SERS) of rhodamine 6G molecules on Hx MoO3 , the SERS enhancement factor reaches as high as 1.1 × 107 with a detection limit at concentration as low as 1 × 10-9 mol L-1 , representing the best among the hitherto reported non-metal systems. The findings not only provide a set of metal-like semiconductor materials with merits of low cost, tunable electronic structure, and plasmonic resonance, but also a general strategy to induce tunable ultrahigh free-carrier concentration in non-metal systems.

A Powerful Electron Accelerator for Producing Neutrons and Radioisotopes

The possibility is considered of using compact linear electron accelerators for the production of medical radioisotopes and neutron therapy. An analysis of calculated data on the flux densities of neutrons and gamma rays shows that photoneutrons and radioisotopes can be effectively produced by using the bremsstrahlung effect generated by a heavy metal target upon its excitation in a range of energies of the giant dipole resonance.

Implementation of nuclear time-dependent density-functional theory and its application to the nuclear isovector electric dipole resonance

Following a previous paper [Y. Shi, Phys. Rev. C 98, 014329(2018)], we present an extension of the density-functional theory to allow for dynamic calculations based on the obtained static Hartree-Fock results. We perform extensive benchmark calculations, by comparing the calculated results with that of an existing code Sky3D. To perform linear-response calculations using the TDDFT method, comparisons have been made with the finite-amplitude quasiparticle random-phase approximation (FAM-QRPA) method. We plan to apply the TDDFT method to a systematic description of the IVD resonances in the Zr, Mo, and Ru isotopes. The strengths of IVD resonances are calculated using two complementary methods: TDDFT and FAM-QRPA methods. For the TDDFT results, additional benchmark calculations have been performed using the well-tested code Sky3D. In these three models, the important ingredients which have major influence on the results, such as time-odd potentials, boundary conditions, smoothing procedures, spurious peaks etc., have been carefully examined. The current TDDFT and the Sky3D codes yield almost identical response functions once both codes use the same time-odd mean fields and absorbing boundary conditions. The strengths of the IVD resonances calculated using the TDDFT and FAM-QRPA methods agree reasonably well with the same position of the giant dipole resonance. Upon seeing a reasonable accuracy offered by the implemented code, we perform systematic TDDFT calculations for spherical Zr and Mo isotopes near $N=50$, where experimental data exist. For neutron-rich Zr, Mo, and Ru isotopes where shape evolution exist we predict the photoabsorption cross sections based on oblate and triaxial minima.

Attosecond electron\u2013spin dynamics in Xe 4d photoionization

The photoionization of xenon atoms in the 70–100 eV range reveals several fascinating physical phenomena such as a giant resonance induced by the dynamic rearrangement of the electron cloud after photon absorption, an anomalous branching ratio between intermediate Xe+ states separated by the spin-orbit interaction and multiple Auger decay processes. These phenomena have been studied in the past, using in particular synchrotron radiation, but without access to real-time dynamics. Here, we study the dynamics of Xe 4d photoionization on its natural time scale combining attosecond interferometry and coincidence spectroscopy. A time-frequency analysis of the involved transitions allows us to identify two interfering ionization mechanisms: the broad giant dipole resonance with a fast decay time less than 50 as, and a narrow resonance at threshold induced by spin-flip transitions, with much longer decay times of several hundred as. Our results provide insight into the complex electron-spin dynamics of photo-induced phenomena.

Nuclear Collective Dynamics in Transport Model With the Lattice Hamiltonian Method

We review the recent progress on studying the nuclear collective dynamics by solving the Boltzmann-Uehling-Uhlenbeck (BUU) equation with the lattice Hamiltonian method treating the collision term by the full-ensemble stochastic collision approach. This lattice BUU (LBUU) method has recently been developed and implemented in a GPU parallel computing technique, and achieves a rather stable nuclear ground-state evolution and high accuracy in evaluating the nucleon-nucleon (NN) collision term. This new LBUU method has been applied to investigate the nuclear isoscalar giant monopole resonances and isovector giant dipole resonances. While the calculations with the LBUU method without the NN collision term (i.e., the lattice Hamiltonian Vlasov method) describe reasonably the excitation energies of nuclear giant resonances, the full LBUU calculations can well reproduce the width of the giant dipole resonance of $^{208}$Pb by including a collisional damping from NN scattering. The observed strong correlation between the width of nuclear giant dipole resonance and the NN elastic cross section suggests that the NN elastic scattering plays an important role in nuclear collective dynamics, and the width of nuclear giant dipole resonance provides a good probe of the in-medium NN elastic cross section.

Microscopic theory of pygmy- and giant resonances: accounting for complex 1p1h$$\otimes $$phonon configurations

The Green function formalism with a consistent account for phonon coupling (PC), based on the self-consistent theory of finite Fermi systems, is applied for pygmy- and giant multipole resonances in magic nuclei with the aim to consider particle–hole (ph) and complex 1p1h $$\otimes $$ phonon configurations. A new equation for the effective field, which describes nuclear polarizability, is obtained. It contains new PC contributions, which are of interest in the energy region under consideration. They are due to: (1) the tadpole effect in the standard ph-propagator, (2) two new induced interactions (caused by the exchange of the ph-phonon) in the second ph-channel and in the particle–particle channels, and (3) the first and second variations of the effective interaction in the phonon field. The general expressions for energies and probabilities of transitions between the ground and excited states are obtained. The qualitative analysis and discussion of the new terms are performed.

Study of giant dipole resonances for neodymium isotopes with an exciton model

The partial photonuclear [Formula: see text], pn) and [Formula: see text] and the total photonuclear cross-sections (the giant dipole resonance (GDR)) have been investigated theoretically for neodymium isotopes, namely [Formula: see text]Nd, using framework of the EMPIRE 3.2.2 code. The energy, width and cross-section parameters of the GDR used in our calculations have been investigated in this paper depending on the deformation parameters of nuclei. The calculated results have been compared with the experimental data and with those calculated using Lorentzian fitting parameters. Our calculations show a good agreement for all isotopes under study and give better results than the results calculated with Lorentzian parameters. Furthermore, the neutron number dependence of the total and partial photonuclear cross-sections has also been discussed. The results appear that the EMPIRE code used is a perfect tool for reproducing the splitting in the GDR for deformed [Formula: see text]Nd isotope in two distinct dipole modes which are perfectly consistent with the experimental results. It has also been shown that the present parameters are suitable parameters for reproducing the GDR for spherical, or nearly spherical, and the deformed ([Formula: see text]Nd) neodymium isotopes. The parameters have been indicating the small deformation in [Formula: see text]Nd, which cannot be shown by the Lorentzian fitting parameters.

Emergent symplectic symmetry in atomic nuclei

Exact symmetry and symmetry-breaking phenomena play a key role in gaining a better understanding of the physics of many-particle systems, from quarks and atomic nuclei, through molecules and galaxies. In nuclei, exact and dominant symmetries such as rotational invariance, parity, and charge independence have been clearly established. Beyond such symmetries, the nature of nuclear dynamics appears to exhibit a high degree of complexity, and only now, we show the fundamental role of an emergent approximate symmetry in nuclei, the symplectic Sp(3,R) symmetry, as clearly unveiled from ab initio studies that start from realistic interactions. In this article, we detail and enhance our recent findings presented in Physical Review Letters 124 (2020) 042501, that establish Sp(3,R) as a remarkably good symmetry of the strong interaction, and point to the predominance of a few equilibrium nuclear shapes (deformed or not) with associated vibrations and rotations that preserve the symplectic Sp(3,R) symmetry. Specifically, we find that the structure of nuclei below the calcium region in their ground state, as well as in their low-lying excited states and giant resonances, respects this symmetry at the 60-80% level.

Constraining isovector nuclear interactions with giant resonances within a Bayesian approach

We put a stringent constraint on the isovector nuclear interactions in the Skyrme-Hartree-Fock model from the centroid energy E−1 of the isovector giant dipole resonance in 208Pb as well as its electric polarizability αD. Using the Bayesian analysis method, E−1 and αD are found to be mostly determined by the nuclear symmetry energy Esym at about ρ⋆=0.05 fm−3 and the isovector nucleon effective mass mv⋆ at the saturation density. At 90% confidence level, we obtain Esym(ρ⋆)=16.4−0.9+1.0 MeV and mv⋆/m=0.79−0.06+0.06.

Electric and magnetic dipole strength inSn112,114,116,118,120,124

Background: There is renewed interest in electric dipole strength distributions for a variety of reasons including the extraction of the dipole polarizability related to properties of the symmetry energy and a measure for the neutron skin thickness, understanding the structure of low-energy E1 strength in nuclei with neutron excess, and establishing the systematics of the isovector giant dipole resonance (IVGDR). Inelastic proton scattering at energies of a few hundred MeV and very forward angles including 0∘ has been established as a tool for the study of electric and magnetic dipole strength distributions in nuclei. Purpose: The present work aims at a systematic investigation of the electric and magnetic dipole strength distributions in the chain of stable even-mass tin isotopes. Methods: Inelastic proton scattering experiments were performed at the Research Center for Nuclear Physics, Osaka, with a 295-MeV beam covering laboratory angles 0∘–6∘ and excitation energies 6–22 MeV. Cross sections due to E1 and M1 excitations were extracted with a multipole decomposition analysis (MDA) and then converted to reduced transition probabilities with the “virtual photon method” for E1 and the “unit cross section method” for M1 excitations, respectively. Including a theory-aided correction for the high-excitation-energy region not covered experimentally, the electric dipole polarizability was determined from the E1 strength distributions. Results: Total photoabsorption cross sections derived from the E1 and M1 strength distributions show significant differences compared to those from previous (γ,xn) experiments in the energy region of the IVGDR. The widths of the IVGDR deduced from the present data with a Lorentz parametrization show an approximately constant value of about 4.5 MeV in contrast to the large variations between isotopes observed in previous work. The IVGDR centroid energies are in good correspondence to expectations from empirical systematics of their mass dependence. Furthermore, a study of the dependence of the IVGDR energies on bulk matter properties is presented. The E1 strengths below neutron threshold show fair agreement with results from (γ,γ′) experiments on Sn112,116,120,124 in the energy region between 6 and 7 MeV, where also isoscalar E1 strength was found for Sn124. At higher excitation energies, large differences are observed, pointing to a different nature of the excited states with small ground-state branching ratios. The isovector spin-M1 strengths exhibit a broad distribution between 6 and 12 MeV in all studied nuclei. Conclusions: The present results contribute to the solution of a variety of nuclear structure problems including the systematics of the energy and width of the IVGDR, the structure of low-energy E1 strength in nuclei, new constraints to energy density functionals (EDFs) aiming at a systematic description of the dipole polarizability across the nuclear chart, from which properties of the symmetry energy can be derived, and the systematics of the isovector spin-M1 strength in heavy nuclei.16 MoreReceived 12 July 2020Accepted 2 September 2020DOI:https://doi.org/10.1103/PhysRevC.102.034327©2020 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsElectromagnetic transitionsH & He induced nuclear reactionsNuclear density functional theoryNuclear structure & decaysPhotonuclear reactionsNuclear Physics

Exotic nuclear shape due to cluster formation at high angular momentum

It is shown, for the first time, how the exotic shapes due to cluster formation at high excitation energy and angular momentum are manifested through giant dipole resonance (GDR) strength function under the framework of the extended quantum molecular dynamics (EQMD) model. The results of EQMD calculation are compared with the existing experimental data of $^{32}\mathrm{S}$ and $^{28}\mathrm{Si}$ formed in the reactions $^{20}\mathrm{Ne}+^{12}\mathrm{C}$ and $^{16}\mathrm{O}+^{12}\mathrm{C}$, respectively, at high angular momenta. It is found that the EQMD predicts the general trend of the experimental GDR strength functions for $^{32}\mathrm{S}$ and $^{28}\mathrm{Si}$ by considering the ring or toroidal configuration, whereas the linear chain configurations with $\ensuremath{\alpha}$ clusters can reproduce the higher-energy peak in $^{32}\mathrm{S}$ and $^{28}\mathrm{Si}$. Thus, the direct signature of the cluster formation at high temperature and angular momentum is the observation of a GDR peak $\ensuremath{\approx}25\phantom{\rule{0.28em}{0ex}}\mathrm{MeV}$ which cannot be predicted within the mean-field calculations. The present result highlights the role of $\ensuremath{\alpha}$ cluster states above the decay threshold, which is still an open field of investigation.

Nucleus giant resonances from an improved isospin-dependent Boltzmann-Uehling-Uhlenbeck transport approach

We have studied the isoscalar giant quadruple resonance (ISGQR) and the isovector giant dipole resonance (IVGDR) in $^{208}$Pb based on an improved isospin-dependent Boltzmann-Uehling-Uhlenbeck transport approach using an improved isospin- and momentum-dependent interaction. With the isoscalar nucleon effective mass and the nucleon-nucleon cross section which reproduces respectively the excitation energy and the width of the ISGQR strength function, the slope parameter of the symmetry energy and the neutron-proton effective mass splitting are constrained respectively within $36<L<62$ MeV and $0.08\delta<(m_{n0}^*-m_{p0}^*)/m<0.42\delta$, by comparing the resulting centroid energy of the IVGDR and the electric dipole polarizability with the experimental data. It is found that nucleon-nucleon collisions have considerable effects on the resulting electric dipole polarizability, which needs to be measured more accurately in order to pin down isovector nuclear interactions.

Jacques Raynal: memories of a physicist

This text is dedicated to the memory of Jacques Raynal. I recall some of the interactions I had with Jacques from 1975 up until his death. I first met Jacques as a young student at Saclay in the mid 1970s and from then on we collaborated frequently. Jacques initiated me into elastic and inelastic scattering calculations in the coupled channels formalism. Within this formalism we calculated the excitation of Giant Resonance by light- or heavy-ion projectiles. We collaborated on the Coulomb corrections implemented in ECIS and later we tested numerically the Incoming Wave Boundary Condition, which is an important assumption when calculating sub-Coulomb fusion cross sections. He was among the first to understand the origin of what we would call the 3- excitation hindrance and suggest solutions.

Photo-neutron cross-section calculations of 54,56Fe, 90,91,92,94Zr, 93Nb and 107Ag Isotopes with newly obtained Giant Dipole Resonance parameters

The knowledge of the interaction of photons with matter is of vital importance to investigate fundamental nuclear physics problems. Giant dipole resonance (GDR) mechanism is dominant up to 30 MeV at photo-absorption cross-section. The photo-absorption cross-section curve against the photon energy displays one or multi-peak Lorentzian functions according to the deformation of the nucleus. Theoretical photo-absorption cross-section calculations generally focus on the estimation of GDR parameters. Theoretical reaction codes use GDR parameters to reproduce photon-induced nuclear reactions. In this study, photo-neutron cross-section calculations of 54,56Fe, 90,91,92,94Zr, 93Nb, and 107Ag isotopes have been done with the TALYS 1.8 and EMPIRE 3.2.2 nuclear reaction codes in the GDR region. During these calculations, both codes were firstly operated by using the predefined and existing GDR parameters within the codes. Later on, a new set of GDR parameters have been obtained by running a Lorentzian model based code in where the available experimental data are also considered. Levenberg-Marquardt algorithm has been used with 10−6 function tolerances and 400 iterations for optimization. These new obtained GDR parameters then replaced with the existing GDR parameters within the TALYS code and the photo-neutron cross-section calculations for the investigated isotopes have been repeated. Ultimately, in order to discuss the outcomes and the effects of using new GDR parameters, obtained results were analyzed by comparing them with the experimental data from the Experimental Nuclear Reaction Data (EXFOR) library.

Multimessenger and multiphysics Bayesian inference for the GW170817 binary neutron star merger

The tidal deformability probability distribution extracted from GW170817 alone, or including multi-messenger information, is confronted to astrophysical and nuclear physics additional constraints within a semi-agnostic approach for the dense matter equation of state. We use Bayesian statistics to combine together low density nuclear physics data, such as the ab-initio predictions based on $\chi$EFT interactions or the isoscalar giant monopole resonance, and astrophysical constraints from neutron stars, such as the maximum mass of neutron stars or the probability density function of the tidal deformability $\tilde{\Lambda}$ obtained from the GW170817 event. The posteriors probability distribution functions are marginalized over several nuclear empirical parameters ($L_\textrm{sym}$, $K_\textrm{sym}$, $Q_\textrm{sat}$ and $Q_\textrm{sym}$), as well as over observational quantities such as the $1.4M_\odot$ radius $R_{1.4}$ and the pressure at twice the saturation density $P(2n_\textrm{sat})$. The correlations between $L_\textrm{sym}$ and $K_\textrm{sym}$ and between $K_\textrm{sat}$ and $Q_\textrm{sat}$ are also further analyzed. Tension is found between the posteriors: the first one is localized in the tidal deformability probability distribution itself, depending whether multi-messenger analysis is included or not, and the second one is between the observational data and the nuclear physics inputs. These tensions impact the predictions for $L_\textrm{sym}$, $K_\textrm{sym}$ and $R_{1.4}$ with centroids which differ by 2-3$\sigma$. Implications for the nuclear equation of state are also discussed.

Compressional-mode resonances in the molybdenum isotopes: Emergence of softness in open-shell nuclei near A = 90

“Why are the tin isotopes soft?” has remained, for the past decade, an open problem in nuclear structure physics: models which reproduce the isoscalar giant monopole resonance (ISGMR) in the “doubly-closed shell” nuclei, 90Zr and 208Pb, overestimate the ISGMR energies of the open-shell tin and cadmium nuclei, by as much as 1 MeV. In an effort to shed some light onto this problem, we present results of detailed studies of the ISGMR in the molybdenum nuclei, with the goal of elucidating where–and how–the softness manifests itself between 90Zr and the cadmium and tin isotopes. The experiment was conducted using the 94,96,98,100Mo(α,α′) reaction at Eα=386 MeV. A comparison of the results with relativistic, self-consistent Random-Phase Approximation calculations indicates that the ISGMR response begins to show softness in the molybdenum isotopes beginning with A=92.

Isoscalar and Isovector Giant Resonances in Closed Shells Nuclei and Bulk Properties of Nuclear Matter

Centroid energies, $$E_{\textrm{CEN}}$$ , of the isoscalar ( $$T=0$$ ) and isovector ( $$T=1$$ ) giant resonances of multipolarities $$L_{m}=0$$ –3 in $${}^{\mathrm{40,48}}$$ Ca, $${}^{\mathrm{68}}$$ Ni, $${}^{\mathrm{90}}$$ Zr, $${}^{\mathrm{116}}$$ Sn, $${}^{\mathrm{144}}$$ Sm, and $${}^{\mathrm{208}}$$ Pb, were calculated within the fully self-consistent spherical Hartree–Fock (HF)-based random-phase approximation (RPA) theory, using 33 different energy density functionals associated with Skyrme-type effective nucleon–nucleon interactions of the standard form commonly employed in the literature. We also calculate the Pearson linear correlation coefficients between each $$E_{\mathrm{CEN}}$$ and each bulk property of nuclear matter (NM), associated with the Skyrme interactions used in the calculations, and determine the sensitivity of $$E_{\mathrm{CEN}}$$ to bulk properties of NM. By comparing the calculated values of $$E_{\textrm{CEN}}$$ to the experimental data, we constrain the values of the bulk NM properties. We find that interactions associated with the values of the NM effective mass, $$m^{\ast}/m=0.70$$ –0.90, incompressibility coefficient, $$K_{\textrm{NM}}=210$$ –240 MeV, and the enhancement coefficient of the energy-weighted sum rule of the isovector giant dipole resonance, $$\kappa=0.25$$ –0.70, best reproduce the experimental data.

Theoretical investigation of giant dipole resonance in 146−152Nd isotopes with QRPA

We investigate the electric dipole ([Formula: see text]) structure properties of the deformed [Formula: see text]Nd nuclei in the giant dipole resonance (GDR) region within the framework of the quasiparticle random-phase approximation (QRPA). Translational and Galilean invariance (TGI) QRPA with separable isovector dipole–dipole residual interaction have been employed for the calculations. We have computed the photoabsorption cross-section and then we have compared with the experimental data. Our calculations revealed that while the photoabsorption cross-section shows a Lorentzian line in the neighborhood of spherical geometry, it starts to shift to an asymmetric shape by increasing deformation in [Formula: see text]Nd isotopes by increasing neutron number. In addition to this, we have also observed that the splitting of the [Formula: see text] strength distribution and the separation between [Formula: see text] and [Formula: see text] branches are increasing. We have calculated the contribution of the electric and magnetic parts of total dipole strength up to 20[Formula: see text]MeV for the nuclei of interest. This calculation shows that the electric part dominates the total dipole strength and [Formula: see text] excitation dominates the electric part.

Electron emission in fast heavy ion impact ionization of C60 and Ne: giant plasmon excitation

We have measured the energy and angle differential ejected electron spectra of C60 as well as Ne atoms in collisions with 4 MeV/u bare fluorine projectile ions. Absolute cross sections have been estimated for electron emission in the energy range of 1 eV–300 eV, including the KLL-Auger electrons for various angles between 30° and 150°. The double differential cross sections for C60 have been compared with the state-of-the-art CDW-EIS model under CNDO approximation as well as with the data for the Ne target. The C60 spectra at all angles show a broad giant plasmon resonance in the low energy region, which is not present in the atomic target data. The angular distribution reveals the dipolar nature of the plasmon excitation. The C K-LL Auger emission from C60 reveals a large angular anisotropy compared to that for a hydrocarbon, e.g. methane target.