Giant Resonance Energy Research Articles

Prompt neutron emission calculations for the photon induced reactions of 238U and 232Th in the giant dipole resonance energy region

Prompt emission calculations for the photon induced fission of 238U and 232Th in the GDR energy region were performed by using (a) a systematic of input parameters for the most probable fragmentation approach (obtained on the basis of only spontaneous and neutron induced fission of actinides) and (b) photo-fission cross section ratios (expressing the fission probabilities at incident energies where multiple fission chances are involved) provided by nuclear reaction calculations performed with the EMPIRE code. The prompt neutron emission results describe well the experimental data recently measured at the laser Compton-scattering γ-ray source of the NewSUBARU facility, validating the use of this input parameter systematic for photon induced fission, too. The modelings and procedures described in this paper can constitute an useful tool for the prediction of prompt neutron emission data in photon induced reactions without any experimental information.

The fine structure of pygmy and giant multipole resonances in nuclei

In connection with the program of planned work on the megascience installation "Intensive Reverse Compton"(INOC) at the Scientific Center of Physics and Mathematics in Sarov, a brief overview of experimental and theoretical results in the field of pygmy- and giant resonance energies is presented. Considered: 1) pygmy-dipole resonance in 208Pb, for which the limit of experimental resolution has already been reached and separate 1 − levels have been identified, 2) the most important physical results of experiments with a resolution of (50–200) keV both for gamma strenght functions, that determine the characteristics of nuclear reactions, and for analysis of non–statistical mechanisms of formation of widths of giant resonances («doorway» states) in the framework of wavelet analysis. Some results in the field of excitation energies (1–5) MeV are also discussed.

Compendium on Monte Carlo simulation of photoneutrons in the Giant Dipole Resonance energy range: The first five elements

Neutrons generated by photonuclear reactions, “photoneutrons”, are encountered in various applications involving high-energy gamma sources, electron accelerators or nuclear reactors. Monte Carlo particle-transport codes are generally used to simulate the emission of photoneutrons, characterize their field or assess their impact on nuclear systems. The aim of this work is to create a compendium on the simulation of photoneutrons using several Monte Carlo codes, i.e., MCNP6, PHITS and TRIPOLI-4, each code being run successively with ENDF/B-VIII.0 and JENDL-5 nuclear data libraries. We study the photoneutron fields produced by 50 elements with their natural isotopic composition from the reaction energy threshold up to 30 MeV, i.e., in the regime of the Giant Dipole Resonance (GDR). The photoneutron fields are characterized according to three observables, i.e., photoneutron current, energy spectrum and angular distribution. This paper presents the results obtained for the first five elements in order of increasing atomic number, i.e., deuterium, beryllium, carbon, nitrogen and oxygen. The compendium could serve as a handbook for users to master the current strengths and limitations of the codes, for code developers to make progress in the sampling of neutron-emitting photonuclear reactions, and more broadly for all researchers working on photoneutrons, whether they are evaluators of nuclear data libraries or experimental nuclear physicists.

Nuclear reactions as a tool to study the microscopic structure of pygmy and giant resonances

An advanced microscopic approach based on energy-density functional theory and the quasiparticle-phonon model has been used to study nuclear excitations up to giant dipole resonance energies. In addition, our nuclear structure model has been extended to include reaction theory. The theoretical spectral distributions compared with experimental data performed with different probes and techniques are able to provide us with information about the microscopic structure of the pygmy dipole resonance as well as its collectivity. Evaluations of electric dipole (E1) transition strengths and branching ratios at low energy reveal different properties of the nuclear excitations and the effect of quasi-continuum coupling. The present studies will support above-neutronthreshold γ experiments at ELI-NP targeting γ decays of giant and pygmy resonances, as well as studies on multi-step γ decays by low-lying states.

Photoneutron cross section measurements on 208Pb

Photoneutron reactions on 208Pb in the Giant Dipole Resonance (GDR) energy range have been investigated at the γ-ray beam line of the NewSUBARU synchrotron radiation facility in Japan. Making use of quasi-monochromatic laser Compton scattering (LCS) γ-ray beams and of a novel flat-efficiency neutron detection system along with associated neutron-multiplicity sorting method, total and partial (γ,xn) photoneutron cross sections with x = 1 to 4 have been measured for 208Pb in a broad energy range covering the neutron threshold up to 38 MeV.

Photofission and photoneutron cross sections for 238U and 232Th

A specific objective of the recent IAEA Coordinated Research Project on Photonuclear Data and Photon Strength Functions (Code F41032; Duration 2016-2019) has been to measure photonuclear cross-section data where needed, for unexplored nuclei and cases of discrepant existing data. A dedicated experimental campaign has been conducted at the laser Compton-scattering γ-ray source of the NewSUBARU synchrotron radiation facility of SPring8, Japan, where photoneutron reactions for 11 nuclei from 9Be to 209Bi have been investigated in the Giant Dipole Resonance energy region. The measurements followed the development of a flat-effi ciency moderated neutron detection array and the associated neutron-multiplicity sorting techniques. The IAEA CRP campaign has been followed at NewSUBARU by new measurements of photofission and photoneutron reactions on 238U and 232Th in the energy range of 5.87 MeV – 20.14 MeV. The neutron-multiplicity sorting of high-multiplicity fission neutron coincidence events has been performed using a dedicated energy dependent, multiple firing statistical treatment. The photoneutron (γ, xn) and photofission (γ, fxn) reactions have been discriminated by considering a Gaussian distribution of prompt-fission-neutrons (PFN) multiplicities predicted by the evaporation theory. We here provide preliminary experimental (γ, n), (γ, 2n) and (γ, F) cross sections, average energies of PFN and of photoneutrons emitted in (γ, n) and (γ, 2n) reactions, as well as the mean number of PFN per fission act. The new 238U cross sections are compared with recent statistical-model calculations performed with the EMPIRE code on existing data.

Spectral distribution and flux of [formula omitted]-ray beams produced through Compton scattering of unsynchronized laser and electron beams

Intense, quasi-monochromatic, polarized γ-ray beams with high and tunable energy produced by Compton scattering of laser photons against relativistic electrons are used for fundamental studies and applications. Following a series of photoneutron cross section measurements in the Giant Dipole Resonance (GDR) energy region performed at the NewSUBARU synchrotron radiation facility, we have developed the eliLaBr Monte Carlo simulation code for characterization of the scattered γ-ray photon beams. The code is implemented using Geant4 and is available on the GitHub repository (https://github.com/dan-mihai-filipescu/eliLaBr). Here we report the validation of the eliLaBr code on NewSUBARU LCS γ-ray beam flux and spectral distribution data and two applications performed with it for asymmetric transverse emittance profiles electron beams, characteristic for synchrotrons.The first application is based on a systematic investigation of transverse collimator offsets relative to the laser and electron beam axis. We show that the maximum energy of the LCS γ-ray beam is altered by vertical collimator offsets, where the edge shifts towards lower energies with the increase in the offset.Secondly, using the eliLaBr code, we investigate the effect of the laser polarization plane orientation on the properties of the LCS γ-ray beams produced with asymmetric emittance electron beams. We show that:1. The use of vertically polarized lasers contributes to the preservation of the LCS γ-ray beam maximum energy edge by increasing the precision in the vertical collimator alignment.2. Under identical conditions for the electron and laser beams phase-space distributions, the energy spectrum of the scattered LCS γ-ray beam changes with the laser beam polarization plane orientation. More precisely, the use of vertically polarized laser beams slightly deteriorates the LCS γ-ray beam energy resolution.

Nuclear incompressibility and speed of sound in uniform matter and finite nuclei

We have extended the compressible liquid-drop model (CLDM) with a density-dependent surface term (eCLDM), which allows for a unified description of both the nuclear ground state energies and the incompressibility modulus in finite nuclei $K_A$. We analyse the role of the nuclear empirical parameters, e.g., $K_{sat}$, $Q_{sat}$, $L_{sym}$ and $K_{sym}$, which contribute to the bulk properties, as well as the role of the finite size contributions. For the bulk properties, the density and isospin dependencies of the nuclear incompressibility in infinite matter are characterized by introducing new empirical parameters, and two new constraints for the value of $K_{sym}$ are suggested. For finite nuclei, we employ a Bayesian approach coupled to a Markov-Chain Monte-Carlo (MCMC) exploration of the parameter space to confront the model predictions of $K_A$ in Zr, Sn and Pb isotopes to the experimental data. We show that $Q_{sat}\approx -950\pm 200$~MeV describes the experimental measurements of $K_A$ in these isotopes. This value is different from the ones deduced from phenomenological nuclear energy density functionals, suggesting a possible explanation of their difficulty to accurately describe Zr, Sn and Pb data all together. In addition we explore the impact of a fictitious measurement of the Giant Monopole Resonance energy in $^{132}$Sn. We show that this measurement, provided it is accurate enough, will allow to better determine $K_{sym}$ and $K_{\tau}$. Finally we explore the properties of the sound speed around saturation density and show the important role of finite size terms in finite nuclei since they reduce the sound speed to approximately half compared to nuclear matter.

Global calculation of two-neutrino double- β decay within the finite amplitude method in nuclear density functional theory

Two-neutrino double-beta ($2\nu\beta\beta$) decay has been used to constrain the neutron-proton part of effective interactions, which in turn is used to compute the nuclear matrix elements for neutrinoless double-beta decay, the observation of which would have important consequences for fundamental physics. We carefully examine $2\nu\beta\beta$ matrix elements within the proton-neutron quasiparticle random-phase approximation with nuclear energy density functionals. We work with functionals that are fit globally to single-beta-decay half-lives and charge-exchange giant-resonance energies, but not to $2\nu\beta\beta$ half-lives themselves, to evaluate the $2\nu\beta\beta$ nuclear matrix elements for all important nuclei, including those whose half-lives have not yet been measured. Such a comprehensive evaluation in large model spaces without configuration truncation requires an efficient computational scheme; we employ a double contour integration within the finite amplitude method. The results generally reproduce the nuclear matrix element extracted from half-lives well, without the use of any of those half-lives in the fitting procedure. We present predictions of the matrix elements in a total of 27 nuclei with half-lives that are still unmeasured.

Nuclear matrix elements for neutrinoless ββ decays and spin-dipole giant resonances

Nuclear matrix elements (NMEs) for neutrinoless double beta decays (DBDs) are required for studying neutrino physics beyond the standard model by DBD. The experimental spin-dipole (SD) giant resonance energy and the SD strength are shown for the first time to be closely related to the DBD-NME, and are used for studying the spin-isospin correlation and the quenching of the axial-vector coupling. So they are used to help the theoretical model calculation of the DBD-NME.

Providing physics guidance in Bayesian neural networks from the input layer: The case of giant dipole resonance predictions

The Bayesian neural network (BNN) has been applied to evaluate and predict the nuclear data. However, how to provide physics guides in BNN is a key but an open question. In this work, the case study on giant dipole resonance (GDR) energy is presented to illustrate the effectiveness and maneuverability of the method to provide physics guides in BNN from input layer. The Spearman's correlation coefficients are applied to assess the statistical dependence between nuclear properties in the ground state and the GDR energies. Then the optimal ground-state properties are employed as the input layer in the BNN for evaluating and predicting the GDR energies. Those selected ground-state properties actively contributes to reduce the predicted errors and avoid the risk of the non-physics divergence. This work gives a demonstration to find effects of the GDR energy by using the BNN without the physics motivated model, which may be helpful for discovering physics effects from the complex nuclear data.

Systematics of electric dipole excitations for odd-mass 233−239U isotopes

We have investigated the dipole strengths from low-lying energy region to giant dipole resonance (GDR) energy region for the 233−239U isotopes in the framework of the Translational and Galilean Invariant-Quasiparticle Nuclear Model (TGI-QPNM) and the total E1 photo-absorption cross sections have been calculated for the nuclei of interest. In the present manuscript, we present the results for the E1 transition properties in the 233−239U isotopes and compare the theoretical values with available experimental data for the first time.

Energy-weighted sum rule for Gamow-Teller giant resonances in high-spin isomeric states of N=Z nuclei

The sum-rule approach and the shell model are used to estimate the energies of Gamow-Teller (GT) giant resonances in high-spin isomeric (HSI) states in $N=Z$ nuclei. The newly derived energy-weighted sum rules show that the GT resonance energies of HSI states are related to the $\ensuremath{\sigma}\ensuremath{\sigma}\ensuremath{\tau}\ensuremath{\tau}$ and $\ensuremath{\sigma}\ensuremath{\sigma}$ interactions. Comparing the results of the sum-rule approach with those of large-scale shell-model calculations for the $^{52}\mathrm{Fe}({12}^{+})$ and $^{94}\mathrm{Ag}({21}^{+})\phantom{\rule{4pt}{0ex}}N=Z$ high-spin isomers, the deduced ${\ensuremath{\kappa}}_{\ensuremath{\sigma}}$, which is the strength of the $\ensuremath{\sigma}\ensuremath{\sigma}$ residual interaction in a simple residual-interaction model, is 2.5 MeV.

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.

Energy density functional and sensitivity of energies of giant resonances to bulk nuclear matter properties

Energy density functional and sensitivity of energies of giant resonances to bulk nuclear matter properties

Optimizing the relativistic energy density functional with nuclear ground state and collective excitation properties

We introduce a new relativistic energy density functional constrained by the ground state properties of atomic nuclei along with the isoscalar giant monopole resonance energy and dipole polarizability in $^{208}$Pb. A unified framework of the relativistic Hartree-Bogoliubov model and random phase approximation based on the relativistic density-dependent point coupling interaction is established in order to determine the DD-PCX parameterization by $\chi^2$ minimization. This procedure is supplemented with the co-variance analysis in order to estimate statistical uncertainties in the model parameters and observables. The effective interaction DD-PCX accurately describes the nuclear ground state properties including the neutron-skin thickness, as well as the isoscalar giant monopole resonance excitation energies and dipole polarizabilities. The implementation of the experimental data on nuclear excitations allows constraining the symmetry energy close to the saturation density, and the incompressibility of nuclear matter by using genuine observables on finite nuclei in the $\chi^2$ minimization protocol, rather than using pseudo-observables on the nuclear matter, or by relying on the ground state properties only, as it has been customary in the previous studies.

Giant resonances in Ca40,48, Ni68, Zr90, Sn116, Sm144 , and Pb208

We present results of centroid energies ${E}_{\mathrm{CEN}}$, of the isoscalar ($T=0$) and isovector ($T=1$) giant resonances of multipolarities $L=0--3$ in $^{40,48}\mathrm{Ca}, ^{68}\mathrm{Ni}, ^{90}\mathrm{Zr}, ^{116}\mathrm{Sn}, ^{144}\mathrm{Sm}$, and $^{208}\mathrm{Pb}$, calculated within the fully self-consistent Hartree-Fock-based random phase approximation theory, using 33 different Skyrme-type effective nucleon-nucleon interactions of the standard form commonly adopted in the literature. We compare the results of our theoretical calculations with the available experimental data. We also study the sensitivity of the calculated ${E}_{\mathrm{CEN}}$ to physical properties of nuclear matter (NM), such as effective mass m*/m, nuclear matter incompressibility coefficient ${K}_{\mathrm{NM}}$, enhancement coefficient \ensuremath{\kappa} of the energy weighted sum rule for the isovector giant dipole resonance and symmetry energy at saturation density, associated with the Skyrme interactions used in the calculations. This is done by determining the Pearson linear correlation coefficient between the calculated ${E}_{\mathrm{CEN}}$ and a certain NM property. Constraining the values of the NM properties, by comparing the calculated values of ${E}_{\mathrm{CEN}}$ to the experimental data, we find that interactions associated with the values of ${K}_{\mathrm{NM}}=210--240\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ and $\ensuremath{\kappa}=0.25--0.70$ best reproduce the experimental data.

Alpha-like resonances in nuclei

We investigate normal dipole oscillations in a system of protons, neutrons and α-particles within the Brink approach. We introduce an effective mass of α-clusters in terms of the spectroscopic factor. The Pauli exclusion principle is taken into account by using the Wildermuth rule. The ratio between alpha and giant resonance energy weighted sum rule (EWSR) is investigated for N = Z and systems. In both cases we notice an unexpected decrease of this ratio versus the increase of the spectroscopic factor. Due to this fact the possibility to experimentally detect α-like oscillations is enhanced in nuclei above 100Sn. The occurrence of the pygmy mode in systems decreases the EWSR for the α-like oscillations.

Isoscalar E0, E1 , and E2 strength in Ca44

Isoscalar giant resonances in $^{44}\mathrm{Ca}$ have been studied with inelastic scattering of 240 MeV \ensuremath{\alpha} particles at small angles including ${0}^{\ensuremath{\circ}}$. A majority of the energy weighted sum rule was identified for $E0$ and $E2$ ($\ensuremath{\approx}70%$), and nearly half was identified for $E1$. The strength distributions are compared with the predictions from Hartree-Fock based random phase approximation calculations with the KDE0v1 Skyrme-type interaction. The giant monopole resonance energy moments for $^{40,44,48}\mathrm{Ca}$ increase with mass, contrary to what would be expected with a negative symmetry energy, ${K}_{\ensuremath{\tau}}$.

Extended Skyrme interactions for nuclear matter, finite nuclei, and neutron stars

Recent progress in theory, experiment and observation challenges the mean field models using the conventional Skyrme interaction, suggesting that the extension of the conventional Skyrme interaction is necessary. In this work, by fitting the experimental data of a number of finite nuclei together with a few additional constraints on nuclear matter using the simulated annealing method, we construct three Skyrme interaction parameter sets, namely, eMSL07, eMSL08 and eMSL09, based on an extended Skyrme interaction which includes additional momentum and density dependent two-body forces to effectively simulate the momentum dependence of the three-body force. The three new interactions can reasonably describe the ground-state properties and the isoscalar giant monopole resonance energies of various spherical nuclei used in the fit as well as the ground-state properties of many other spherical nuclei, nicely conform to the current knowledge on the equation of state of asymmetric nuclear matter, eliminate the notorious unphysical instabilities of symmetric nuclear matter and pure neutron matter up to a very high density of $1.2$ fm$^{-3}$, and simultaneously support heavier neutron stars with mass larger than two times solar mass. One important difference of the three new interactions is about the prediction of the symmetry energy at supra-saturation densities, and these new interactions are thus potentially useful for the determination of the largely uncertain high-density symmetry energy in future. In addition, a comparison is made for the predictions of nuclear matter, finite nuclei and neutron stars with the three new interactions versus those with three typical interactions BSk22, BSk24 and BSk26 from Brussels group.