NN Interaction Research Articles

Microscopic nucleon spectral function for finite nuclei featuring two- and three-nucleon short-range correlations: The model versus ab initio calculations for three-nucleon systems

The main features of the convolution model which, in the region of two-nucleon (2N) and three-nucleon (3N) short-range correlations (SRC), describes the one-nucleon momentum distribution n(k_1) and the spectral function P(k_1,E) in terms of a convolution integral involving the relative n_{rel}(k_{rel}) and the center-of-mass n_{c.m.}(K_{c.m.}) momentum distributions of a nucleon-nucleon pair, are illustrated in detail. It is stressed that the model, which stems from the universal property of factorization exhibited by the nuclear wave function at short inter-nucleon distances, is only applicable in a well-defined region of k_{rel} and K_{c.m.}; it is shown, in particular, that the requirement of factorization introduces a severe constraint on the values of k_{rel} and K_{c.m.} that appear in the convolution integral. Using ab-initio relative and c.m. momentum distributions for ^3He, the validity of the convolution model is investigated by comparing the model spectral function and momentum distributions with the ones resulting from ab-initio calculations performed with realistic local NN interaction of the Argonne family. It is shown that when the constraint on the value of k_{rel} and K_{c.m.} are correctly taken into account and only 2N SRC are taken into account, the convolution model is in good agreement with the ab-initio spectral function in the region of the peak exhibited by the latter, whereas far from the peak, particularly at high values of the removal energy, the model spectral function can be qualitatively reconciled with the ab-initio spectral function only by considering the effects of 3N SRC. As for the nucleon momentum distribution, the effects of 3N SRC appears to be very small.

Quantitative analysis of the fusion cross sections using different microscopic nucleus-nucleus interactions

The fusion cross sections for reactions involving medium and heavy nucleus-nucleus systems are investigated near and above the Coulomb barrier using the one-dimensional barrier penetration model. The microscopic nuclear interaction potential is computed by four methods, namely: the double-folding model based on a realistic density-dependent M3Y NN interaction with a finite-range exchange part, the Skyrme energy density functional in the semiclassical extended Thomas-Fermi approximation, the generalized Proximity potential, and the Akyuz-Winther interaction. The comparison between the calculated and the measured values of the fusion excitation functions indicates that the calculations of the DFM give quite satisfactory agreement with the experimental data, being much better than the other methods. New parameterized forms for the fusion barrier heights and positions are presented. Furthermore, the effects of deformation and orientation degrees of freedom on the distribution of the Coulomb barrier characteristics as well as the fusion cross sections are studied for the reactions 16O + 70Ge and 28Si + 100Mo. The calculated values of the total fusion cross sections are compared with coupled channel calculations using the code CCFULL and compared with the experimental data. Our results reveal that the inclusion of deformations and orientation degrees of freedom improves the comparison with the experimental data.

Description of resonant states in the shell model

A technique for describing scattering states within the nuclear shell model is proposed. This technique is applied to scattering of nucleons by $\alpha$ particles based on ab initio No-Core Shell Model calculations of $^5$He and $^5$Li nuclei with JISP16 NN interaction.

Multinucleon short-range correlation model for nuclear spectral functions: Theoretical framework

We develop a theoretical approach for nuclear spectral functions at high missing momenta and removal energies based on the multi-nucleon short-range correlation~(SRC) model. The approach is based on the effective Feynman diagrammatic method which allows to account for the relativistic effects important in the SRC domain. In addition to two-nucleon SRC with center of mass motion we derive also the contribution of three-nucleon SRCs to the nuclear spectral functions. The latter is modeled based on the assumption that 3N SRCs are a product of two sequential short range NN interactions. This approach allowed us to express the 3N SRC part of the nuclear spectral function as a convolution of two NN SRCs. Thus the knowledge of 2N SRCs allows us to model both two- and three-nucleon SRC contributions to the spectral function. The derivations of the spectral functions are based on the two theoretical frameworks in evaluating covariant Feynman diagrams: In the first, referred as virtual nucleon approximation, we reduce Feynman diagrams to the time ordered noncovariant diagrams by evaluating nucleon spectators in the SRC at their positive energy poles, neglecting explicitly the contribution from vacuum diagrams. In the second approach, referred as light-front approximation, we formulate the boost invariant nuclear spectral function in the light-front reference frame in which case the vacuum diagrams are generally suppressed and the bound nucleon is described by its light-cone variables such as momentum fraction, transverse momentum and invariant mass.

Cluster decay half-lives of trans-lead nuclei based on a finite-range nucleon–nucleon interaction

Nuclear cluster radioactivity is investigated using microscopic potentials in the framework of the Wentzel–Kramers–Brillouin approximation of quantum tunneling by considering the Bohr–Sommerfeld quantization condition. The microscopic cluster–daughter potential is numerically constructed in the well-established double-folding model. A realistic M3Y-Paris NN interaction with the finite-range exchange part as well as the ordinary zero-range exchange NN force is considered in the present work. The influence of nuclear deformations on the cluster decay half-lives is investigated. Based on the available experimental data, the cluster preformation factors are extracted from the calculated and the measured half lives of cluster radioactivity. Some useful predictions of cluster emission half-lives are made for emissions of known clusters from possible candidates, which may guide future experiments.

Prediction for a Four-Neutron Resonance.

We utilize various abinitio approaches to search for a low-lying resonance in the four-neutron (4n) system using the JISP16 realistic NN interaction. Our most accurate prediction is obtained using a J-matrix extension of the no-core shell model and suggests a 4n resonant state at an energy near E_{r}=0.8 MeV with a width of approximately Γ=1.4 MeV.

N3LO NN interaction adjusted to light nuclei in ab exitu approach

We use phase-equivalent transformations to adjust off-shell properties of similarity renormalization group evolved chiral effective field theory NN interaction (Idaho N3LO) to fit selected binding energies and spectra of light nuclei in an ab exitu approach. We then test the transformed interaction on a set of additional observables in light nuclei to verify that it provides reasonable descriptions of these observables with an apparent reduced need for three- and many-nucleon interactions.

Low energy α+16O scattering in the orthogonality condition model

The orthogonality condition model (OCM) is used to describe α+16O scattering at low energies. A double folding potential with density-dependent effective NN interactions is used as the local potential of the model. The energies and widths of α-cluster resonances and differential cross sections are calculated. The results are compared to one obtained using the standard potential approach, without the nonlocal interaction of the OCM.

Microscopic analysis of 10,11Be elastic scattering on protons and 12C and breakup processes of 11Be within the 10Be+n cluster model

The elastic scattering cross-sections of 10,11Be on protons and 12C at energy E < 100 MeV/nucleon using microscopically calculated optical potentials (OP) are presented. The real OP is obtained by a folding procedure with effective NN interactions, while the imaginary OP is estimated within the high energy approximation (HEA). The spin-orbit part of the OP is also included. The characteristics of the breakup processes of 11Be on different nuclear targets are also considered. The cross-sections of diffractive breakup and stripping reactions of 11Be on 9Be, 93Nb, 181Ta and 238U at energy E = 63 MeV/nucleon and the longitudinal momentum distributions of 10Be fragments produced in the breakup of 11Be on these nuclei are presented. The results are in a good agreement with the available experimental data, in particular the obtained widths of about 50 MeV/c are closed to the empirical ones.

DFMSPH14: A C-code for the double folding interaction potential of two spherical nuclei

This is a new version of the DFMSPH code designed to obtain the nucleus–nucleus potential by using the double folding model (DFM) and in particular to find the Coulomb barrier. The new version uses the charge, proton, and neutron density distributions provided by the user. Also we added an option for fitting the DFM potential by the Gross–Kalinowski profile. The main functionalities of the original code (e.g. the nucleus–nucleus potential as a function of the distance between the centers of mass of colliding nuclei, the Coulomb barrier characteristics, etc.) have not been modified. New version program summaryProgram title: DFMSPH14Catalog identifier: AEFH_v2_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEFH_v2_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland.Licensing provisions: GNU General Public License, version 3No. of lines in distributed program, including test data, etc.: 7211No. of bytes in distributed program, including test data, etc.: 114404Distribution format: tar.gzProgramming language: CComputer: PC and MacOperation system: Windows XP and higher, MacOS, Unix/LinuxMemory required to execute with typical data: below 10 MbyteClassification: 17.9Catalog identifier of previous version: AEFH_v1_0Journal reference of previous version: Comp. Phys. Comm. 181 (2010) 168Does the new version supersede the previous version?: YesNature of physical problem: The code calculates in a semimicroscopic way the bare interaction potential between two colliding spherical nuclei as a function of the center of mass distance. The height and the position of the Coulomb barrier are found. The calculated potential is approximated by an analytical profile (Woods–Saxon or Gross–Kalinowski) near the barrier. Dependence of the barrier parameters upon the characteristics of the effective NN forces (like, e.g. the range of the exchange part of the nuclear term) can be investigated.Method of solution: The nucleus–nucleus potential is calculated using the double folding model with the Coulomb and the effective M3Y NN interactions. For the direct parts of the Coulomb and the nuclear terms, the Fourier transform method is used. In order to calculate the exchange parts, the density matrix expansion method is applied.Typical running time: less than 1 minute.Reason for new version: Many users asked us how to implement their own density distributions in the DFMSPH. Now this option has been added. Also we found that the calculated Double-Folding Potential (DFP) is approximated more accurately by the Gross–Kalinowski (GK) profile. This option has been also added.

Uncertainty quantification of effective nuclear interactions

We give a brief review on the development of phenomenological NN interactions and the corresponding quantification of statistical uncertainties. We look into the uncertainty of effective interactions broadly used in mean field calculations through the Skyrme parameters and effective field theory counterterms by estimating both statistical and systematic uncertainties stemming from the NN interaction. We also comment on the role played by different fitting strategies on the light of recent developments.

Investigation of the nuclear system using the D-dimensional wave equation

We calculate the nucleus-nucleus interaction potential with the DFM using the wavefunctions of two colliding nuclei. The wavefunctions are obtained by solving the D-dimensional wave equation using hyperspherical formalism. The calculations were assumed to be of finite-range and the density dependence of the NN interaction is accounted for. The results have been compared with calculations of zero-range approximation. To evaluate the formalism used to calculate the nucleus wavefunction, the numerical results for the interaction potential and the scattering cross-section are presented.

Lightest Kaonic Nuclear Clust

We present our study of kaonic three-body KNN , KNN and KKK and four-body KNNN , and KKNN clusters within the framework of a potential model using the method of hyperspherical functions in momentum representation. To perform a numerical calculations for the bound state energy of the light kaonic system, we use a set of different potentials for the nucleon-nucleon and KN interactions, as well as for the kaon-kaon interaction. The calculations show that a quasibound state energy is not sensitive to the NN interaction, and it shows very strong dependence on the KN potential. We also compare our results with those obtained using different theoretical approaches. The theoretical discrepancies in the binding energy and width for the lightest kaonic system related to the different NN and KN interactions are addressed.

Neutron-neutron quasifree scattering inndbreakup at 10 MeV

The neutron-deuteron (nd ) breakup reaction provides a rich environment for testing theoretical models of the neutron-neutron (nn ) interaction. Current theoretical predictions based on rigorous ab-initio calculations agree well with most experimental data for this system, but there remain a few notable discrepancies. The cross section for nn quasifree (QFS) scattering is one such anomaly. Two recent experiments reported cross sections for this particular nd breakup configuration that exceed theoretical calculations by almost 20% at incident neutron energies of 26 and 25 MeV [1, 2]. The theoretical values can be brought into agreement with these results by increasing the strength of the 1 S0 nn potential matrix element by roughly 10%. However, this modification of the nn effective range parameter and/or the 1 S0 scattering length causes substantial charge-symmetry breaking in the nucleon-nucleon force and suggests the possibility of a weakly bound di-neutron state [3].We are conducting new measurements of the cross section for nn QFS in nd breakup. The measurements are performed at incident neutron beam energies below 20 MeV. The neutron beam is produced via the 2 H(d , n )3 He reaction. The target is a deuterated plastic cylinder. Our measurements utilize time-of-flight techniques with a pulsed neutron beam and detection of the two emitted neutrons in coincidence. A description of our initial measurements at 10 MeV for a single scattering angle will be presented along with preliminary results. Also, plans for measurements at other energies with broad angular coverage will be discussed.

Double-Polarized pd Scattering and Test of Time-reversal Invariance

The integrated proton-deuteron cross section σ˜ for the case of transversal polarization ppy of the proton and tensor polarization Pxz of the deuteron provides a null test signal for time-reversal invariance violating but P-parity conserving effects. The corresponding experiment is planned at COSY to measure the observable σ˜. Here we consider in general case the status of the null-test observable in pd scattering, calculate σ˜ within the Glauber theory of the double-polarized pd scattering at 100 - 1000 MeV and study the contribution of the deuteron S- and D-waves for several type of the T-odd NN interactions.

Properties of4He and6Li with improved chiral EFT interactions

We present recent results for 4 He and 6 Li obtained with improved NN interactions derived from chiral effective field theory up to N4 LO. The many-body calculations are performed order-by-order in the chiral expansion. At N3 LO and N4 LO additional renormalization using the Similarity Renormalization Group is adopted to improve numerical convergence of the many-body calculations. We discuss results for the ground state energies, as well as the magnetic moment and the low-lying spectrum of 6 Li.

Statistical error propagation inab initiono-core full configuration calculations of light nuclei

We propagate the statistical uncertainty of experimental NN scattering data into the binding energy of $^3$H and $^4$He. We also study the sensitivity of the magnetic moment and proton radius of the $^3$H to changes in the NN interaction. The calculations are made with the no-core full configuration method in a sufficiently large harmonic oscillator basis. For those light nuclei we obtain $\Delta E$($^3$H) = 0.015 MeV and $\Delta E$($^4$He) = 0.055 MeV.

Two-neutron “halo” from the low-energy limit of neutron–neutron interaction: Applications to drip-line nuclei 22C and 24O

The formation of two-neutron “halo”, a low-density far-extended surface of weakly-bound two neutrons, is described using the neutron–neutron (nn) interaction fixed at the low-energy nn scattering limit. This method is tested for loosely-bound two neutrons in 24O, where a good agreement with experimental data is found. It is applied to halo neutrons in 22C in two ways: with the 20C core being closed or correlated (due to excitations from the closed core). This nn interaction is shown to be strong enough to produce a two-neutron halo in both cases, locating 22C on the drip line, while 21C remains unbound. A unique relation between the two neutron separation energy, S2n, and the radius of neutron halo is presented. New predictions for S2n and the radius of neutron halo are given for 22C. The appearance of Efimov states is also discussed.

The Effect of Local and Non-Local Potentials on BCS Solutions for Some Even-Even Nuclei

We study the like-particle pairings using the BCS approximation applied for different eveneven nuclear isotopes using different realistic potentials for the NN interaction. First we solve the Schrodinger equation using a deformed axially symmetric Woods-Saxon potential. For the pairing interaction the interaction G-matrix is calculated using local potentials (Argonne V18 and Nijmegen II) and non-local potentials (Bonn-CD and Nijmegen I). A study of the effect of these different realistic potentials on the pairing strengths, average pairing gaps, Fermi energies, and occupation probabilities of protons and neutrons is introduced. We find that the pairing strength values calculated by the local potentials are greater than that calculated by the non-local potentials. We find that only one of the BCS outputs, the pairing energy gap, is slightly affected by using different types of realistic potentials.

Influence of the next-nearest neighbor exchange interaction on the thin-film spin‐wave spectrum

We study the order of modes in the spin‐wave spectrum of a ferromagnetic thin film. In our calculations we use the Heisenberg model taking into account the exchange interaction between the nearest (NN) and next-nearest (NNN) neighbors and including the single-ion anisotropy term. We elucidate the effect of the NNN exchange coupling on both the spectrum of propagating spin waves and the spin‐wave resonance (SWR) spectrum. We show that with sufficiently strong antiferromagnetic NNN interaction the order of modes in the spin‐wave spectrum is reversed at the center of the Brillouin zone, with the lowest mode optic and the highest one acoustic. This effect allows to infer the character of the NNN interaction from the resonance peak intensity pattern in the SWR spectrum. We also show that the reversed order of modes can be related to in-plane spin‐wave propagation. Surprisingly, this dynamic reversal can occur even if both the NN and NNN exchange interactions are ferromagnetic. This effect should be observed in Brillouin light scattering and spin-polarized electron energy loss spectra as a collapse, followed by a spectrum with a reversed intensity pattern with changing wave-vector length.