Nuclear Chart Research Articles

Nuclear chart in covariant density functional theory with dynamic correlations: From oxygen to tin * * Supported by the National Key R&D Program of China (2018YFA0404400, 2017YFE0116700) and the National Natural Science Foundation of China (11621131001, 11875075, 11935003, 11975031)

Nuclear masses of even-even nuclei with the proton number (O to Sn isotopes) from the proton drip line to neutron drip line are investigated using the triaxial relativistic Hartree-Bogoliubov theory with the relativistic density functional PC-PK1. Further, the dynamical correlation energies (DCEs) associated with the rotational motion and quadrupole-shaped vibrational motion are taken into account by the five-dimensional collective Hamiltonian (5DCH) method. The root-mean-square deviation with respect to the experimental masses reduces from 2.50 to 1.59 MeV after the consideration of DCEs. The inclusion of DCEs has little influence on the position of drip lines, and the predicted numbers of bound even-even nuclei between proton and neutron drip lines from O to Sn isotopes are 569 and 564 with and without DCEs, respectively.

Predictions of nuclear charge radii and physical interpretations based on the naive Bayesian probability classifier

Background: The nuclear charge radii provide direct information for the nuclear structures. In recent years, many pioneering researches have been devoted to the nuclear charge radii based on the Bayesian neural networks (BNN) method. Purpose: The neural networks always have complex structure. To analyze the data relationships clearly, a statistical method is introduced to study the nuclear properties by combining the sophisticated nuclear models with the naive Bayesian probability (NBP) classifier. Method: In the framework of the NBP method, the predicted charge radii are interpreted as the most reasonable expectations. The prior probabilities and the condition probabilities are computed by the experimental data and the raw results of nuclear models. The posterior probabilities of expectations are updated by the Bayesian formula. The predicted charge radii are regarded as the expectations with maximum probability. Moreover, the abilities of global optimizations and extrapolations of the NBP method are analyzed to demonstrate the availability of the NBP method. Results: For the HFB model and the semiempirical formula, the accuracy of charge radii predictions improves 41% and 32% after NBP refinements, respectively. Calculations also illustrate that the NBP method has robust extrapolating abilities, and the charge radii of unknown regions in the nuclear chart can be predicted by the NBP method. Conclusions: The NBP method contains the advantages of local relations and global descriptions, which can provide fine-tuning for the theoretical results of sophisticated nuclear models. The method proposed in this paper can also be used for other research of nuclear properties.

A Global Model of β−-Decay Half-Lives Using Neural Networks

Statistical modeling of nuclear data using artificial neural networks (ANNs) and, more re- cently, support vector machines (SVMs), is providing novel approaches to systematics that are complementary to phenomenological and semi-microscopic theories. We present a global model of β−-decay halflives of the class of nuclei that decay 100% by β− mode in their ground states. A fully-connected multilayered feed forward network has been trained using the Levenberg- Marquardt algorithm, Bayesian regularization, and cross-validation. The halflife estimates gen- erated by the model are discussed and compared with the available experimental data, with previous results obtained with neural networks, and with estimates coming from traditional global nuclear models. Predictions of the new neural-network model are given for nuclei far from stability, with particular attention to those involved in r-process nucleosynthesis. This study demonstrates that in the framework of the β−-decay problem considered here, global models based on ANNs can at least match the predictive performance of the best conventional global models rooted in nuclear theory. Accordingly, such statistical models can provide a valuable tool for further mapping of the nuclidic chart.

Properties of exotic nuclei and their linkage to the nucleonic interaction

The structure of exotic nuclei sheds new light on the linkage of the nuclear structure to the nucleonic interaction. The self-consistent mean-field (SCMF) theories are useful to investigate this linkage, which are applicable to many nuclei covering almost the whole range of the nuclear chart without artificial truncation of model space. For this purpose, it is desired to develop effective interaction for the SCMF calculations well connected to the bare nucleonic interaction. Focusing on ground-state properties, I show the results of SCMF calculations primarily with the Michigan-three-range-Yukawa (M3Y)-type semi-realistic interaction, M3Y-P6 and M3Y-P6a to be precise, and discuss in detail how the nucleonic interaction affects the structure of nuclei including those far off the [Formula: see text]-stability. The central channels of the effective interaction are examined by the properties of the infinite nuclear matter up to the spin dependence and the isospin dependence. While experimental information of the infinite matter is obtained by extrapolating systematic data on finite nuclei in principle, it is not easy to constrain the spin dependence and the isospin dependence without connection to the bare nucleonic interaction. The noncentral channels play important roles in the shell structure of the finite nuclei. The tensor force is demonstrated to affect [Formula: see text]- or [Formula: see text]-dependence of the shell structure and the magic numbers, on which the spin–isospin channel in the central force often acts cooperatively. By using the M3Y-P6 interaction, the prediction of magic numbers is given in a wide range of the nuclear chart, which is consistent with almost all the available data. In relation to the erosion of magic numbers in unstable nuclei, effects of the tensor force on the nuclear deformation are also argued, being opposite between nuclei at the [Formula: see text]- and the [Formula: see text]-closed magicities. Qualitatively consistent with the [Formula: see text]-force effect on the [Formula: see text]-splitting suggested from the chiral effective field theory, the density-dependent LS channel, which is newly introduced in M3Y-P6a, reproduces the observed kinks in the differential charge radii at the [Formula: see text]-closed magic numbers and predicts anti-kinks at the [Formula: see text]-closed magic numbers. The pairing correlation has significant effects on the halos near the neutron drip line. A new mechanism called “unpaired-particle haloing” is disclosed.

Probing the Tz=−3/2 nuclei via magnetic moment measurements

The neutron-deficient region of the nuclear chart provides unique opportunities to study several important effects near the proton-drip line pertaining to nuclear structure and nuclear astrophysics.The present article focuses on nuclei with isospin Tz=−3/2 in terms of the spin polarization and the ground state magnetic moment. An experiment on measuring the ground state moment pf 35K by employing the β-NMR technique leads to several interesting results that pose challenging questions to theory.

Status of JENDL

Recent progress and future plan of the JENDL project are summarized. Two special purpose files were released recently. One is Photo-nuclear Data File 2016 (JENDL/PD-2016) which contains the data of photo-nuclear reaction cross sections covering a wide area of the nuclear chart. The other one is the JENDL Activation Cross Section File for Nuclear Decommissioning 2017 (JENDL/AD-2017) which provides production cross sections of radioactive nuclei by neutrons. A special purpose file JENDL/ImPACT-2018 dedicated to transmutation of long-lived fission products will be released in 2019. Regarding the general-purpose file, we are preparing to release the next version, which would be made available by 2022 as JENDL-5. Evaluation efforts on nuclides across wide range of nuclei form light to heavy have being made. The first test version JENDL-5α1 was created in 2018. The evaluated data will be updated on the basis of benchmark tests on reactor criticalities and neutron shieldings.

Evaluation of nuclear structure data and its spin-offs

Evaluation of nuclear structure data is a world wide effort to standardize the published nuclear data. This standardization led to generation of table of isotopes, Nuclear Data sheets, Nuclear Wallet Cards etc. This paper deals with two aspects of evaluation of nuclear structure data. First, the problems arising out of some of the recent publications and how to tackle them at pre-publication stage. Second, there is large amount of experimental data available on the NNDC site 1 . Of these data the half-life values, spin and parity is the most important set of values to understand the nucleon-nucleon interaction within a given nucleus. However, it is observed in our work that the quantum of half-life, spin and parity values measured, in comparison to the number of excited states, in any given nuclei, is very low. Thus, indicating that very few experimental results are available in terms of half-life measurements, spin measurements and determination of parity. This survey besides being an indicator of the quantum of measurements carried out can also be a guide to future experimentalists by highlighting the areas of nuclear chart where measurements are fewer in number.

Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure

Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure

Towards ab initio structure and response calculations across the nuclear chart

Starting from the Argonne V18 nucleon-nucleon interaction and using the Unitary Correlation Operator Method, a correlated interaction vucOM has been constructed, which is suitable for calculations within restricted Hilbert spaces. In this work we employ the vucOM in Hartree-Fock, perturbation-theory and RPA calculations. First results are reported on the ground-state properties of various closed-shell nuclei, as well as some excited states. Our results provide valuable information on the properties of the VUCOM and guidance to further optimization. The above scheme offers the prospect of ab initio calculations in nuclei throughout the nuclear chart. It can be used in conjunction with other realistic NN interactions as well, both local and non-local. Various many-body methods can be employed, such as Second RPA, QRPA, Shell Model, etc.

Study of dipole excitations in even-even 156-166Dy with QRPA using the Gogny force

The success encountered in the systematic studies of the electric and magnetic strength functions for almost all even-even nuclei proves the quality of our HFB+QRPA calculations which use the Gogny interaction within the whole nuclear chart. In this paper, we study the dipole electromagnetic strength distribution in 158-166Dy. The scalar or the vector nature, in the isospin as well as in the spin space, is analysed according to transition density for some of the M1 excitations in 162Dy.

Experimental study of the 2n-transfer reaction 138Ba(18O,16O)140Ba in the projectile energy range 61–67 MeV

Two-neutron transfer reactions serve as an important tool for nuclear-structure studies in the neutron-rich part of the nuclear chart. In this paper, we report on the first experimental attempt to populate the excited states of140Ba employing the 2n-transfer reaction138Ba(18O,16O)140Ba. 140Ba is highly important, as it is placed on the onset of octupole correlations and the lifetimes of its excited states are completely unknown, with the sole exception of the first state. The experiment was carried out at the Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN–HH) in Magurele, Romania. Lower limits on the lifetimes of the ground state band up to the state are reported. Furthermore, relative cross-sections regarding the 2n-transfer reaction with respect to the fusion and the total inelastic reaction channels have been deduced. Further investigation directions of the nuclear structure of 140Ba are also discussed.

Influence of the tensor interaction on heavy-ion fusion cross sections

[Background] While the tensor interaction has been shown to significantly affect the nuclear structure of exotic nuclei, its influence on nuclear reactions has only recently been investigated. The primary reason for this neglect is the fact that most studies of nuclear dynamics do not include the tensor force at all in their models. Indeed, only a few Skyrme parametrizations consider the tensor interaction in parameter determination. With modern research facilities extending our ability to probe exotic nuclei, a correct description of nuclear dynamics and heavy-ion fusion is vital to both supporting and leading experimental efforts. [Method] Fusion cross sections are calculated using ion-ion potentials generated by the fully microscopic density-constrained time-dependent Hartree-Fock (DC-TDHF) method with the complete Skyrme tensor interaction. [Results] For light nuclei, the tensor force only slightly changes the sub-barrier fusion cross sections at very low energies. Heavier nuclei, however, begin to exhibit a substantial hindrance effect in the sub-barrier region. This effect is strongest in spin-unsaturated systems, though can manifest in other configurations as well. Static, ground state deformation effects of the tensor force can also affect cross sections by shifting the fusion barrier. [Conclusions] The tensor interaction has a measurable effect on the fusion cross sections of nuclei spanning the nuclear chart. The effect comes from both static effects present in the ground state and dynamic processes arising from the time evolution of the system. This motivates the development of a modern Skyrme parameter set that includes all time-odd and tensor terms and that studies moving forward should include the tensor force to ensure a more robust and complete description of nuclei.

Half-lives of Sr73 and Y76 and the consequences for the proton dripline

The half-lives of seven nuclei have been determined in the neutron-deficient mass-70 region following their production via fragmentation of a 345 MeV/nucleon Xe124 primary beam on a 740 mg/cm2 Be9 target at the RI Beam Factory, RIKEN. The results include two new (Sr73 and Y76) half-lives and a more precise measurement for the ground-state half-life of Sr74. The new results are discussed with reference to previously published calculations that predict the location of the proton dripline in the light Sr and Y region of the nuclear chart. In addition, differences in the ground-state structure of Rb72 and Y76 are discussed with the aid of density functional theory calculations. These provide a possible explanation for why Rb72 undergoes proton decay while the α-conjugate nucleus Y76 predominantly undergoes β+ decay.

Toward scalable many-body calculations for nuclear open quantum systems using the Gamow Shell Model

Drip-line nuclei have very different properties from those of the valley of stability, as they are weakly bound and resonant. Therefore, the models devised for stable nuclei can no longer be applied therein. Hence, a new theoretical tool, the Gamow Shell Model (GSM), has been developed to study the many-body states occurring at the limits of the nuclear chart. GSM is a configuration interaction model based on the use of the so-called Berggren basis, which contains bound, resonant and scattering states, so that inter-nucleon correlations are fully taken into account and the asymptotes of extended many-body wave functions are precisely handled. However, large complex symmetric matrices must be diagonalized in this framework, therefore the use of very powerful parallel machines is needed therein. In order to fully take advantage of their power, a 2D partitioning scheme using hybrid MPI/OpenMP parallelization has been developed in our GSM code. The specificities of the 2D partitioning scheme in the GSM framework will be described and illustrated with numerical examples. It will then be shown that the introduction of this scheme in the GSM code greatly enhances its capabilities.

Superheavy nuclei and hypernuclei: extending the limits of the nuclear chart

Emergence of superheavy nuclei and hypernuclei, two fields of intense research in nuclear physics, has made a big impact on the nuclear chart; while the discovery of the superheavy oganesson has completed the seven full rows of the periodic table, discovery of several exotic hypernuclei have added a third dimension, called strangeness, to the existing nuclear chart. Highlights of some recent developments in these two fields are presented

Parameter optimization for the latest quark-meson coupling energy-density functional

The Quark--Meson--Coupling (QMC) model self-consistently relates the dynamics of the internal quark structure of a hadron to the relativistic mean fields arising in nuclear matter. It offers a natural explanation to some open questions in nuclear theory, including the origin of many-body nuclear forces and their saturation, the spin-orbit interaction and properties of hadronic matter at a wide range of densities. The QMC energy density functionals QMC-I and QMC$\pi$-I have been successfully applied to calculate ground state observables of finite nuclei in the Hartree-Fock + BCS approximation, as well as to predict properties of dense nuclear matter and cold non-rotating neutron stars. Here we report the latest development of the model, QMC$\pi$-II, extended to include higher order self-interaction of the $\sigma$ meson. A derivative-free optimization algorithm has been employed to determine a new set of the model parameters and their statistics, including errors and correlations. QMC$\pi$-II predictions for a wide range of properties of even-even nuclei across the nuclear chart, with fewer adjustable parameters, are comparable with other models. Predictions of ground state binding energies of even-even isotopes of superheavy elements with Z$>$96 are particularly encouraging.

Uncertainties in νp-process nucleosynthesis from Monte Carlo variation of reaction rates

ABSTRACT It has been suggested that a νp-process can occur when hot, dense, and proton-rich matter is expanding within a strong flux of antineutrinos. In such an environment, proton-rich nuclides can be produced in sequences of proton captures and (n, p) reactions, where the free neutrons are created in situ by $\overline{\nu }_\mathrm{e}+\mathrm{p} {\rightarrow} \mathrm{n}+\mathrm{e}^+$ reactions. The detailed hydrodynamic evolution determines where the nucleosynthesis path turns off from N = Z line and how far up the nuclear chart it runs. In this work, the uncertainties on the final isotopic abundances stemming from uncertainties in the nuclear reaction rates were investigated in a large-scale Monte Carlo approach, simultaneously varying more than 10 000 reactions. A large range of model conditions was investigated because a definitive astrophysical site for the νp-process has not yet been identified. The present parameter study provides, for each model, identification of the key nuclear reactions dominating the uncertainty for a given nuclide abundance. As all rates appearing in the νp-process involve unstable nuclei, and thus only theoretical rates are available, the final abundance uncertainties are larger than those for nucleosynthesis processes closer to stability. Nevertheless, most uncertainties remain below a factor of 3 in trajectories with robust nucleosynthesis. More extreme conditions allow production of heavier nuclides but show larger uncertainties because of the accumulation of the uncertainties in many rates and because the termination of nucleosynthesis is not at equilibrium conditions. It is also found that the solar ratio of the abundances of 92Mo and 94Mo could be reproduced within uncertainties.

Development of a gas filled magnet for FIPPS phase II

The Fission Product Prompt γ-ray Spectrometer (FIPPS) is a new instrument of the Institut Laue-Langevin (ILL) for the spectroscopy of nuclei produced after neutron induced reactions. The future upgrade of the instrument aims to explore the neutron-rich region of the nuclear chart with higher selectivity by identifying the fragments produced after neutron induced fission. The Gas-Filled-Magnet (GFM) technique has been chosen in order to obtain a good mass separation (<4 amu at A = 150) and a large geometrical and momentum acceptance (>50 msr and Δ P/P > 10%). A GFM design consisting of a 1/r magnetic field index and Thales circle-shaped entrance and exit magnet edges is proposed. The characteristic of the magnet is presented with realistic magnetic field calculations and Monte-Carlo simulations.

The N = 126 factory: A new facility to produce very heavy neutron-rich isotopes

A new facility, the N = 126 factory, is currently under construction at Argonne National Laboratory. It will use multi-nucleon transfer reactions to create neutron-rich isotopes of very heavy elements for studies of interest to the formation of the A ∼ 195 abundance peak in the r-process. This region of the nuclear chart is difficult to access by standard fragmentation or spallation reactions and as a result has remained mostly unexplored. The nuclei of interest, very neutron-rich isotopes around Z = 70–95, will be produced by multi-nucleon exchange of a high intensity 10 MeV/u heavy-ion beam on the most neutron-rich stable isotopes of heavy elements such as 198Pt and 238U. This reaction mechanism can transfer a large number of neutrons and create very neutron-rich isotopes with larger than mb cross-section. The reaction mechanism is a nuclear surface process and the reaction products come out close to the grazing angle, which makes them very difficult to collect. The N = 126 factory circumvents this difficulty by using a unique large high-intensity RF gas catcher, similar to the one currently in operation at CARIBU, to collect the target-like reaction products and transform them into a low-energy beam that will then be mass separated with a medium resolution electromagnetic separator (ΔM/M ≃ 1/1500), followed by an RFQ buncher and an MR-TOF (ΔM/M ≃ 1/100,000) system. The extracted radioactive beams will be essentially pure and available at low-energy for mass measurements with the CPT mass spectrometer or decay study with the X-array.

Negative Parity States in 39Cl Configured by Crossing Major Shell Orbits**Supported by JSPS and CNRS under the Japan-France Research Cooperative Program, the Grant-in-Aid for Scientific Research on Innovative Areas “Toward new frontiers: Encounter and synergy of state-of-the-art astronomical detectors and exotic quantum beams”, JSPS/MEXT KAKENHI under Grant Nos JP18HO3692 and JP18H05462, the National Key R&D Program of China (2018YFA0404403), and

Traditional “magic numbers” were once regarded as immutable throughout the nuclear chart. However, unexpected changes were found for unstable nuclei around N = 20. With both proton and neutron numbers around the magic number of 20, the neutron-rich 39Cl isotope provides a good test case for the study of the quantum-state evolution across the major shell. In the present work, the negative parity states in 39Cl are investigated through the β decay spectroscopy of 39S. Newly observed γ transitions together with a new state are assigned into the level scheme of 39Cl. The spin parity of 5/2− for the lowest negative parity state in 39Cl is reconfirmed using the combined γ transition information. These systematic observations of the negative parity states in 39Cl allow a comprehensive comparison with the theoretical descriptions. The lowest 5/2− state in 39Cl remains exotic in terms of comparisons with existing theoretical calculations and with the neighboring isotopes having similar single-particle configurations. Further experimental and theoretical investigations are suggested.