CD-Bonn Nucleon-nucleon Potential Research Articles

Measurement of the [formula omitted] neutron-neutron effective range in neutron-deuteron breakup

We report the most precise determination of the S01 neutron-neutron effective range parameter (rnn) from neutron-neutron quasifree scattering in neutron-deuteron breakup. The experiment setup utilized a collimated beam of 15.5 MeV neutrons and an array of eight neutron detectors positioned at angles sensitive to several quasifree scattering kinematic configurations. The two neutrons emitted from the breakup reaction were detected in coincidence and time-of-flight techniques were used to determine their energies. The beam-target luminosity was measured in-situ with the yields from neutron-deuteron elastic scattering. Rigorous Faddeev-type calculations using the CD Bonn nucleon-nucleon potential were fit to our cross-section data to determine the value of rnn. The analysis was repeated using a semilocal momentum-space regularized N4LO+ chiral interaction potential. We obtained values of rnn=2.86±0.01(stat)±0.10(sys) fm and rnn=2.87±0.01(stat)±0.10(sys) fm using the CD Bonn and N4LO+ potentials, respectively. Our results are consistent with charge symmetry and previously reported values of rnn.

Microscopic structure of the one-phonon 2+ states of Po208

The lifetimes of the 2 1 + and 4 1 + states of Po 208 were measured in the α -transfer reaction Pb 204 ( C 12 , Be 8 ) Po 208 by γ -ray spectroscopy utilizing the recoil distance Doppler shift method. The newly extracted transition strengths alongside ones of the decay of the 2 2 + state were compared to the results of large-scale shell-model calculations using an effective interaction derived from the realistic CD-Bonn nucleon-nucleon potential. The comparison indicates the importance of the quadrupole isovector excitations in the valence shell for a fine tuning of the two-body matrix elements of the shell-model interaction.

New shell-model investigation of the lead-208 mass region: Spectroscopic properties and collectivity

Within the large-scale shell-model framework, an investigation of even-even nuclei in the vicinity of the $^{208}\mathrm{Pb}$ closed core is reported in the present work. The calculations of the low-lying state energies and the electromagnetic transitions of the Pb, Po, Rn, Ra, and Th nuclei with $126\ensuremath{\le}N\ensuremath{\le}134$ are performed using a new effective interaction H208 derived from CD-Bonn nucleon-nucleon potential, through the ${V}_{\mathrm{low}\text{\ensuremath{-}}k}$ procedure. A special focus is devoted to the degree of the collectivity, where a transitional region from spherical nuclear shape to weakly collective behavior is revealed.

Short-range correlations for 0νββ decay and low-momentum NN potentials

We approach the calculation of the nuclear matrix element of the neutrinoless double-β decay process, considering the light-neutrino-exchange channel, by way of the realistic shell-model. In particular the focus of our work is spotted on the role of the short-range correlations, which should be taken into account because of the short-range repulsion of the realistic potentials. Our shell-model wave functions are calculated using an effective Hamiltonian derived from the high-precision CD-Bonn nucleon-nucleon potential, the latter renormalized by way of the so-called Vlow-k approach. The renormalization procedure decouples the repulsive high-momentum component of the potential from the low-momentum ones by the introduction of a cutoff Λ, and is employed to renormalize consistently the two-body neutrino potentials to calculate the nuclear matrix elements of candidates to this decay process in mass interval ranging from A = 76 up to A = 136. We study the dependence of the decay operator on the choice of the cutoff, and compare our results with other approaches that can be found in present literature.

Neutron-neutron quasifree scattering in neutron-deuteron breakup at 10 MeV

New measurements of the neutron-neutron quasifree scattering cross section in neutron-deuteron breakup at an incident neutron energy of 10.0 MeV are reported. The experiment setup was optimized to evaluate the technique for determining the integrated beam-target luminosity in neutron-neutron coincidence cross-section measurements in neutron-deuteron breakup. The measurements were carried out with a systematic uncertainty of $\pm 5.6 \%$. Our data are in agreement with theoretical calculations performed using the CD-Bonn nucleon-nucleon potential in the Faddeev formalism. The measured integrated cross section over the quasifree peak is $20.5 \pm 0.5 \text{(stat)} \pm 1.1 \text{(sys)}$ mb/sr$^2$ in comparison with the theory prediction of 20.1 mb/sr$^{2}$. These results validate our technique for determining the beam-target luminosity in neutron-deuteron breakup measurements.

Large scale shell model calculations for the yrast line of 138Xe

We have adopted an importance sampling iterative matrix diagonalization algorithm to compute a large scale shell model calculation of the yrast spectrum of 138Xe up to high spin thereby extending a previous calculation confined to low-lying angular momenta. An effective nucleon–nucleon interaction derived from the CD-Bonn nucleon-nucleon potential is used to compute energies, E2 transition probabilities, and occupation numbers. A satisfactory agreement with the experimental data is reached.

Large–scale shell model calculations for 140Xe

This paper presents the results of a large-scale shell model calculations of the yrast spectrum of 140Xe. We extend the previous calculations confined to low-lying angular momenta to high-spin states apply- ing the same importance sampling iterative matrix diagonalization algorithm. Excitation energies and transi- tion probabilities are obtained by using an effective nucleon-nucleon interaction derived from the CD-Bonn nucleon-nucleon potential. A satisfactory agreement with the experimental data and the previous results for low lying states is achieved.

Pairing properties of realistic effective interactions

We investigate the pairing properties of an effective shell-model interaction defined within a model space outside 132 Sn and derived by means of perturbation theory from the CD-Bonn free nucleon-nucleon potential. It turns out that the neutron pairing component of the effective interaction is significantly weaker than the proton one, which accounts for the large pairing gap difference observed in the two-valence identical particle nuclei 134 Sn and 134 Te. The role of the contribution arising from one particle-one hole excitations in determining the pairing force is discussed and its microscopic structure is also analyzed in terms of the multipole decomposition.

Two-neutron transfer in Sn isotopes beyond theN=82shell closure

We have performed microscopic distorted-wave Born approximation calculations of differential cross sections for the two reactions $^{136}\mathrm{Sn}(p,t)^{134}\mathrm{Sn}$ and $^{134}\mathrm{Sn}(t,p)^{136}\mathrm{Sn}$, which are within reach of near-future experiments with radioactive ion beams. We have described the initial and final nuclear states in terms of the shell model, employing a realistic low-momentum two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential that has already proved quite successful in describing the available low-energy spectrum of $^{134}\mathrm{Sn}$. We discuss the main features of the predicted cross sections for the population of the low-lying yrast states in the two nuclei considered.

Evolution of single-particle states beyond132Sn

We have performed shell-model calculations for the two one valence-neutron isotones $^{135}$Te and $^{137}$Xe and the two one valence-proton isotopes $^{135,137}$Sb. The main aim of our study has been to investigate the evolution of single-particle states with increasing nucleon number. To this end, we have focused attention on the spectroscopic factors and the effective single-particle energies. In our calculations, we have employed a realistic low-momentum two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential that has already proved quite successful in describing the spectroscopic properties of nuclei in the $^{132}$Sn region. Comparison shows that our results reproduce very well the available experimental data. This gives confidence in the evolution of the single-particle states 4 figures predicted by the present study.

Shell-model study of single-neutron strength fragmentation in137Xe

We have performed shell-model calculations for the nucleus $^{137}$Xe, which was recently studied experimentally using the $^{136}$Xe($d,p$) reaction in inverse kinematics. The main aim of our study has been to investigate the single-neutron properties of the observed states, focusing attention on the spectroscopic factors. We have employed a realistic low-momentum two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential that has already proved quite successful in describing the spectroscopic properties of nuclei in the $^{132}$Sn region. Comparison shows that our calculations reproduce very well the experimental excitation energies and yield spectroscopic factors that come close to those extracted from the data.

Monopole-optimized effective interaction for tin isotopes

We present a systematic configuration-interaction shell model calculation on the structure of light tin isotopes with a new global optimized effective interaction. The starting point of the calculation is the realistic CD-Bonn nucleon-nucleon potential. The unknown single-particle energies of the $1d_{3/2}$, $2s_{1/2}$ and $0h_{11/2}$ orbitals and the T=1 monopole interactions are determined by fitting to the binding energies of 157 low-lying yrast states in $^{102-132}$Sn. We apply the Hamiltonian to analyze the origin of the spin inversion between $^{101}$Sn and $^{103}$Sn that was observed recently and to explore the possible contribution from interaction terms beyond the normal pairing.

High resolution spectroscopy of112Sn through the114Sn(p,t)112Sn reaction

The ${}^{114}$Sn($p$,$t$)${}^{112}$Sn reaction has been investigated in a high resolution experiment at incident proton energy of 22 MeV. Angular distributions for 28 transitions to levels of ${}^{112}$Sn up to the excitation energy of 3.624 MeV have been measured. The spin and parity identification has been carried out by means of a distorted-wave Born approximation (DWBA) analysis, performed by using conventional Woods-Saxon potentials. A shell-model study of ${}^{112}$Sn nucleus has been performed using a realistic two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential. The energy spectra have been calculated and compared with the experimental ones, while the theoretical two-nucleon spectroscopic amplitudes, evaluated in a truncated seniority space, have been used in the microscopic DWBA calculation of the cross-section angular distributions.

G9/2nuclei and neutron-proton interaction

We have performed shell-model calculations for nuclei below 100Sn, focusing attention on the two N=Z nuclei 96Cd and 92Pd, the latter having been recently the subject of great experimental and theoretical interest. We have considered nuclei for which the 0g9/2 orbit plays a dominant role and employed a realistic low-momentum two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential. This implies that no phenomenological input enters our effective Hamiltonian. The calculated results for 92Pd are in very good agreement with the available experimental data, which gives confidence in our predictions for 96Cd. An analysis of the wave functions of both 96Cd and 92Pd is performed to investigate the role of the isoscalar spin-aligned coupling.

Microscopic approach to the shell model: study of nuclei north-east of 48Ca

We report on shell-model calculations for nuclei with valence nucleons outside 48Ca wherein a fully microscopic approach is adopted. Namely, the single-particle energies and the matrix elements of the two-body interaction are derived theoretically starting from the high-precision CD-Bonn nucleon-nucleon potential, renormalized by way of the Vlow−k approach. This has been done within the framework of the time-dependent degenerate linked-diagram perturbation theory. Our results compare satisfactorily with a large amount of experimental data.

High-resolution measurement of theSn118,124(p,t)Sn116,122reactions: Shell-model and microscopic distorted-wave Born approximation calculations

The $^{118,124}\mathrm{Sn}$($p$,$t$)$^{116,122}\mathrm{Sn}$ reactions have been investigated in high-resolution experiments at incident proton energies of 24.6 and 25 MeV, respectively. Angular distributions for 55 transitions to levels of $^{116}\mathrm{Sn}$ and 63 transitions to levels of $^{122}\mathrm{Sn}$, up to excitation energies of $~3.850$ and $~4.000$ MeV, respectively, have been measured. The spin and parity identification was carried out by means of a distorted-wave Born approximation (DWBA) analysis, performed by using conventional Woods-Saxon potentials. A shell-model study of $^{116}\mathrm{Sn}$ and $^{122}\mathrm{Sn}$ nuclei was performed using a realistic two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential. The doubly magic nucleus $^{132}\mathrm{Sn}$ was assumed as a closed core, with the 16 and 10 valence neutron holes occupying the five levels of the 50-82 shell. The energy spectra have been calculated and compared with the experimental ones, and the theoretical two-nucleon spectroscopic amplitudes, evaluated in a truncated seniority space, have been used in the microscopic DWBA calculation of some cross-section angular distributions of both reactions.

Realistic low-momentum effective interactions and nuclear structure near double closed shells

We report on a shell-model study of nuclei with four valence nucleons in the 132Sn and 208Pb regions. This aims at investigating to what extent the striking similarity existing between the low-energy properties of 134Sb and 210Bi persists when adding a pair of identical particles. We employ realistic low-momentum effective interactions derived from the CD-Bonn nucleon-nucleon potential through use of the Vlow-k approach. The calculated results are in very good agreement with the available experimental data and emphasize the persistence of a close resemblance between the spectroscopy of the two regions when moving away from the one proton-one neutron systems.

Ground-State and Single-Particle Energies of Nuclei aroundO16,Ca40, andNi56from Realistic Nucleon-Nucleon Forces

We perform ab initio calculations for nuclei around 16O, 40Ca, and 56Ni using realistic nucleon-nucleon forces. In particular, 56Ni is computed as the heaviest nucleus in this kind of ab initio calculation. Ground-state and single-particle energies including three-body-cluster effects are obtained within the framework of the unitary-model-operator approach. It is shown that the CD-Bonn nucleon-nucleon potential gives quite good results close to the experimental values for all nuclei in the present work.

Shell-model study of theN=82isotonic chain with a realistic effective Hamiltonian

We have performed shell-model calculations for the even- and odd-mass $N=82$ isotones, focusing attention on low-energy states. The single-particle energies and effective two-body interaction both have been determined within the framework of the time-dependent degenerate linked-diagram perturbation theory, starting from a low-momentum interaction derived from the CD-Bonn nucleon-nucleon potential. In this way, no phenomenological input enters our effective Hamiltonian, whose reliability is evidenced by the good agreement between theory and experiment.

Spectroscopic study of neutron-rich calcium isotopes with a realistic shell-model interaction

We have studied neutron-rich calcium isotopes in terms of the shell model, employing a realistic effective interaction derived from the CD-Bonn nucleon-nucleon potential. The short-range repulsion of the potential is renormalized by way of the ${V}_{\mathrm{low}\ensuremath{-}\mathrm{k}}$ approach. The calculated results are in very good agreement with the available experimental data, thus supporting our predictions for the hitherto unknown spectra of $^{53\ensuremath{-}56}\mathrm{Ca}$ nuclei. In this context, the possible existence of an $N=34$ shell closure is discussed.