Structure Of Atomic Nuclei Research Articles

Uncertainties of nuclear level density estimated using Bayesian neural networks* *Supported by the the National Natural Science Foundation of China (12275359, 12375129, 11875323, 11961141003), the National Key R&D Program of China (2023YFA1606402), the Continuous Basic Scientific Research Project, the Funding of China Institute of Atomic Energy (YZ222407001301, YZ232604001601), and the Leading Innovation Project of the CNNC (LC192209000701, LC202309000201)

Nuclear level density (NLD) is a critical parameter for understanding nuclear reactions and the structure of atomic nuclei; however, accurate estimation of NLD is challenging owing to limitations inherent in both experimental measurements and theoretical models. This paper presents a sophisticated approach using Bayesian neural networks (BNNs) to analyze NLD across a wide range of models. It uniquely incorporates the assessment of model uncertainties. The application of BNNs demonstrates remarkable success in accurately predicting NLD values when compared to recent experimental data, confirming the effectiveness of our methodology. The reliability and predictive power of the BNN approach not only validates its current application but also encourages its integration into future analyses of nuclear reaction cross sections.

PROBING THE NUCLEAR STRUCTURE OF EXOTIC 33Mg ISOTOPE

Research on the nuclear structure of exotic isotopes, such as 33Mg, is an exciting and cuttingedge field of nuclear physics. Exotic isotopes are typically those that are far from the stable region of the nuclear chart and often exhibit unique properties that can help us better understand the fundamental forces and structure of atomic nuclei. In this paper the largescale shell model calculations are performed within the model spaces SDPFMU, to study the positive- and negative-parity energy levels and electromagnetic transitions in the exotic 33Mg isotope. Core-polarization effects on reduced transition probability are introduced through first order perturbation theory, which allows for higher energy configurations through excitations of nucleons from core orbits to that outside model space up to . The corepolarization effects have been improved the agreement of B(E2) with their corresponding experimental data, and have ignorable effect on B(M1)

Quantum entanglement patterns in the structure of atomic nuclei within the nuclear shell model

Quantum entanglement offers a unique perspective into the underlying structure of strongly-correlated systems such as atomic nuclei. In this paper, we use quantum information tools to analyze the structure of light and medium-mass berillyum, oxygen, neon and calcium isotopes within the nuclear shell model. We use different entanglement metrics, including single-orbital entanglement, mutual information, and von Neumann entropies for different equipartitions of the shell-model valence space and identify mode-entanglement patterns related to the energy, angular momentum and isospin of the nuclear single-particle orbitals. We observe that the single-orbital entanglement is directly related to the number of valence nucleons and the energy structure of the shell, while the mutual information highlights signatures of proton–proton and neutron–neutron pairing, as well as nuclear deformation. Proton and neutron orbitals are weakly entangled by all measures, and in fact have the lowest von Neumann entropies among all possible equipartitions of the valence space. In contrast, orbitals with opposite angular momentum projection have relatively large entropies, especially in spherical nuclei. This analysis provides a guide for designing more efficient quantum algorithms for the noisy intermediate-scale quantum era.

New method for level-lifetime measurements with thick scintillators

Level lifetimes provide key insight into the structure of atomic nuclei and serve as stringent tests of theoretical descriptions. Though several methods for determining level lifetimes exist for both reaction measurements and decay studies, here the focus is on techniques involving the direct measurement of time differences between population and subsequent depopulation of excited states. The techniques presented herein are broadly applicable across multiple timing ranges, but the approach is specifically described for the βγ timing method. A multi-step, amplitude-dependent time walk correction and timing resolution corrections were employed to address the data analysis complications that arise from using thick scintillators for electron detection. Subsequently, a new Monte Carlo method utilizing measured detector responses obtained from the data, coupled with chi-square minimization, is presented for extracting excited state lifetimes ≳ 100 picoseconds. The framework of this Monte Carlo method is developed for the decay of a state in 68Zn with a known 1.6 ps half life, which is considered prompt given the detection sensitivity of the technique, and then benchmarked using two other excited states in neutron-rich Ni isotopes with 120(34) ps and 1.05(3) ns half lives. Using this new method which takes into account the thick scintillator used, these same half lives were measured to be 135(10) ps and 1.04(24) ns, respectively. The overall good agreement demonstrates the validity of the technique.

Probing triaxial deformation of atomic nuclei in high-energy heavy ion collisions

The structure of atomic nuclei is shown to influence a collection of observables measured in relativistic heavy-ion collisions. Details of the nuclear shape---here its triaxial nature---and of its fluctuations are reflected in the angular correlations between the detected particles, establishing a connection between high-energy nuclear collisions and low-energy nuclear structure.

Exact sum rules with approximate ground states

Electromagnetic and weak transitions tell us a great deal about the structure of atomic nuclei. Yet modeling transitions can be difficult: it is often easier to compute the ground state, if only as an approximation, than excited states. One alternative is through transition sum rules, in particular the non-energy-weighted and energy-weighted sum rules, which can be computed as expectation values of operators. We investigate by computing sum rules for a variety of nuclei, comparing the numerically exact full configuration-interaction shell model, as a reference, to Hartree–Fock, projected Hartree–Fock, and the nucleon pair approximation. These approximations yield reasonable agreement, which we explain by prior work on the systematics of transition moments.

Empirical Consequences of Emergent Mass

The Lagrangian that defines quantum chromodynamics (QCD), the strong interaction piece of the Standard Model, appears very simple. Nevertheless, it is responsible for an astonishing array of high-level phenomena with enormous apparent complexity, e.g., the existence, number and structure of atomic nuclei. The source of all these things can be traced to emergent mass, which might itself be QCD’s self-stabilising mechanism. A background to this perspective is provided, presenting, inter alia, a discussion of the gluon mass and QCD’s process-independent effective charge and highlighting an array of observable expressions of emergent mass, ranging from its manifestations in pion parton distributions to those in nucleon electromagnetic form factors.

Ab initio short-range-correlation scaling factors from light to medium-mass nuclei

High-energy scattering processes, such as deep inelastic scattering (DIS) and quasielastic (QE) scattering provide a wealth of information about the structure of atomic nuclei. The remarkable discovery of the empirical linear relationship between the slope of the European Muon Collaboration (EMC) effect in DIS and the short-range-correlation (SRC) scaling factors a2 in QE kinematics is naturally explained in terms of scale separation in effective field theory. This explanation has powerful consequences, allowing us to calculate and predict SRC scaling factors from ab initio low-energy nuclear theory. We present ab initio calculations of SRC scaling factors for a nucleus A relative to the deuteron a2(A/d) and relative to in light and medium-mass nuclei. Our framework further predicts that the EMC effect and SRC scaling factors have minimal or negligible isovector corrections.

Novel Excitation Modes in Nuclei: Experimental and Theoretical Investigation on Multiple Chiral Doublets

As a microscopic quantal many-body system, the structure of atomic nucleus is understood by measuring and interpreting its responses to all kinds of probes. The responses manifest in different kinds of energy excitation spectra with specific energy and angular momentum (spin), and link with electric and magnetic transition rates.

A Generic Description Model for the Structure of Atomic Nucleus with New Interpretation of the Strong Forces

The present investigation is motivated by finding and developing an easily understandable solution in the context of unified quantum and gravitational theories. Model-based methods are applied, with emphasis on structural descriptions by introducing some strong hypotheses. A subset of the introduced hypotheses led to a surprising understanding of the internal structure and construction of quarks, neutrons, protons and more complex atomic nuclei. The research work therefore focused mainly on the model-based interpretation of subatomic processes. The results obtained so far and presented in this paper are new. They consist of a generic description model for the structure of atomic nuclei. This model contains two important structural links that originate from the initial phase of the cosmological big bang. They hold atomic parts together and are involved in many known nuclear fusion and fission processes. Modifications of them, including the electron-positron annihilation process, are necessary and will be described. A new interpretation of the strong forces from the Standard Model is possible and will be given. In addition, the formation processes for electron and positron particles are considered. Based on the structural relationships, a deeper understanding of matter transformations (transmutations), early cosmological processes and dark matter has been achieved. All challenges of this work are the logical conclusions from the used hypotheses on two structural links. They need to be further investigated and verified by theoretical and experimental works. The postulated particle in this paper, as accompanying product in the electron-positron annihilation, will play a major role for the future investigations.

Structure and properties of atomic nuclei in the theory of compressible oscillating ether

In the work, based on the equations of the compressible oscillating ether, derived from the laws of classical mechanics, ether mathematical models of the nuclei of atoms of chemical elements are constructed. It is shown that the nucleus of any atom is a superposition of perturbation waves of ether density in several protons and several neutrons, having a common center and propagating around a common axis in one direction or in opposite directions, that is, having unidirectional or oppositely directed spins. Formulas for the values of internal energies, masses, magnetic moments, and binding energies of atomic nuclei are derived, with an accuracy of fractions of a percent coinciding with their experimental values. Formulas for calculating the radii of atomic nuclei are obtained. Answers are given to many topical questions about the structure of atomic nuclei that modern atomic physics is not capable of answering, for example: why there are no nuclei consisting only of protons or only of neutrons; what is the nature of the nuclear forces holding together protons and neutrons in the nucleus; why the sizes of atomic nuclei practically do not depend on the atomic number of the chemical element; why the Coulomb barrier of the nucleus selectively works; why the fragments of the decomposition of heavy elements into two nuclides are asymmetric; what is the reason for the different percentage in nature of different isotopes of the same chemical element?

The model of complex structure of atomic nucleus and living body

The model of complex structure of atomic nucleus and living body

The Relativistic Theory of Electromagnetic Interactions

Quantum – mechanical problem on electron motion in Coulomb field plays the fundamental role in the modern physics, because solution of this problem provides the most realistic model of atomic structure. In nowadays the model of meson atom is of the same importance. Indeed, the mesoatom is unstable, hence the study of interaction of mesons with atomic nuclei can provide the valuable information on the nature of hadronic interactions and structure of atomic nucleus. The mesoatoms arise in the process of scattering of the negatively charged pions in matter. The pions captured by the target atoms populate initially the highly excited atomic orbits and then go down to 2p and 1s atomic states via cascade of radiative transitions. As far as the meson mass exceeds the electron mass for the two orders of magnitude then the mesonic atom orbit radius is much smaller than the radius of electron atom orbits. For example, the radius of the lowest mesonic orbits becomes comparable with the atomic nucleus size in the case of nucleus charge 12 Z [1]. As a result, for meson in 2p state the probability to annihilate on atomic nucleus is higher than the probability to decay radiatively in 2 1 p s transition. In the atoms with the nucleus charge 40 Z the radiative transitions disappear before the cascade reaches the 2p state. In the case of atoms with more heavy nuclei even the 3d states can not often be occupied. Thus the study of the cascade x-ray spectra of mesonic atoms provides the information on the efficiency of meson interaction with the different nuclei. The nonrelativistic Schredinger theory produces the atomic spectrum in zero-order approximation which does not include fine and hyperfine structure. The atomic spectrum calculated in the frames of the Dirac relativistic theory includes the fine structure. The hyperfine atomic structure can be calculated with the help of the invariant perturbation theory methods, which are based on the field quantization theory. The smallness parameter of invariant perturbation theory is the product of the hyperfine structure constant and nucleus charge, Z . Hence, the atoms with the nucleus charge of 1 Z are out of the frames of the perturbation theory and therefore they are of special interest. This interest is due to a number of reasons: Firstly, the precise mathematical calculations of hyperfine atomic structure can be based on the non-perturbative theory which is valid for arbitrary value of parameter Z . Secondly, the Dirac theory predicts that at 1 Z the energy eigenvalues become complex. It means that the corresponding atomic states are unstable, i.e. the lifetime of these states is finite [2-4].

Hydrodynamic models of the structure of atomic nuclei

Hydrodynamic models of the structure of atomic nuclei

Shell structure, emerging collectivity, and valence p-n interactions

The structure of atomic nuclei depends on the interactions of its constituents, protons and neutrons. These interactions play a key role in the development of configuration mixing and in the onset of collectivity and deformation, in changes to the single particle energies and magic numbers, and in the microscopic origins of phase transitional behavior. Particularly important are the valence proton-neutron interactions which can be studied experimentally using double differences of binding energies extracted from high-precision mass measurements. The resulting quantities, called δV pn , are average interaction strengths between the last two protons and the last two neutrons. Focusing on the Z=50-82, N=82-126 shells, we have considered a number of aspects of these interactions, ranging from their relation to the underlying orbits, their behaviour near close shells and throughout major shells, their relation to the onset of collectivity and deformation, and the appearance of unexpected spikes in δV pn values for a special set of heavy nuclei with nearly equal numbers of valence protons and neutrons. We have calculated spatial overlaps between proton and neutron Nilsson orbits and compared these with the experimental results. Finally we also address the relation between masses (separation energies), changes in structure and valence nucleon number.

HELIOS: A New Approach to Reactions in Inverse Kinematics

The study of nuclear structure with transfer reactions has enjoyed a great revitalization with the advent of radioactive beams. Worldwide, many facilities are now capable of delivering radioactive-ion beams at energies near the Coulomb barrier. Measurements that have built up the basis of much of what we know about the structure of atomic nuclei can now be made far away from the valley of stability [1–6]. Many sophisticated charged-particle detector arrays have been developed to take advantage of these beams. These arrays, typically combining silicon-detector and gas-ionization or scintillator technologies, revealed many new and interesting facets of nuclear structure. Discoveries include new features of orbitals in the shell model, better data on effective single-particle energies, and demonstrated the effects of aspects of the nucleon-nucleon interactions in nuclei such as the tensor force. All of these become much more interesting as nuclei approach the limits of stability.

NUSTAR – presence and prospects of nuclear structure research at GSI and FAIR

New experimental methods at rare-isotope facilities including in-flight separation, storage rings, and traps, setups for reaction studies with beams of exotic nuclei in reversed kinematics and large gamma arrays give new insights into the structure of atomic nuclei at the limits of stability. The discoveries of new isotopes and elements, as well as new phenomena including one and two proton decay, nuclear halos and skins as well as coexistence of nuclear shapes will be discussed. Workhorses are the UNILAC and SIS accelerators in combination with the in-flight separators SHIP and FRS. Physics at the ESR storage ring at GSI addresses the interaction of atomic and nuclear physics and large-scale explorations of the landscape of nuclear masses. A brief outlook on the future, NUSTAR at FAIR will be given.

Recent progress in theoretical studies of nuclear magnetic moments

Nuclear magnetic moment is highly sensitive to the underlying structure of atomic nuclei and therefore serves as a stringent test of nuclear models. The advanced nuclear structure models have been successful in analyzing many nuclear structure properties, but they still cannot provide a satisfactory description of nuclear magnetic moments. Recently attempts to summarize the present understanding on nuclear magnetic moments in both relativistic and non-relativistic theoretical models have been made. The detailed contents are covered in the issue entitled “Nuclear magnetic moments and related topics” (in Sci China Phys Mech Astron, Vol. 54, No. 2, 2011). In this paper some of the related achievements will be highlighted.

Introduction to shell structure in exotic nuclei

The nuclear shell model is a benchmark for the description of the structure of atomic nuclei. The magic numbers associated with closed shells have long been assumed to be valid across the whole nuclear chart. Investigations in recent years of nuclei far away from nuclear stability at facilities for radioactive ion beams have revealed that the magic numbers may change locally in those exotic nuclei leading to the disappearance of classic shell gaps and the appearance of new magic numbers. These changes in shell structure also have important implications for the synthesis of heavy elements in stars and stellar explosions. In this review a brief overview of the basics of the nuclear shell model will be given together with a summary of recent theoretical and experimental activities investigating these changes in the nuclear shell structure.

Ambartsumian’s paradigm for the activity of galactic nuclei and the evolution of galaxies

Ambartsumian’s paradigm for the creation of galaxies owing to the decay of denser matter is examined. The roots of this concept can be found in the very earliest papers of Ambartsumian on quantum fields and the structure of atomic nuclei. In the early 1930’s his papers contained new ideas regarding the ejection by one physical object of another which had not originally existed inside the first. The basic observational data which served as the basis for the final formulation of the new concept are described. Special attention is devoted to those objects and phenomena, which, upon further study, have confirmed the validity of Ambartsumian’s reasoning and arguments. It is noted that the discovery of Hubble expansion’s acceleration of the universe opened up new possibilities for the interpretation of activity phenomena in terms of Ambartsumian’s concept. The further extension of this concept is discussed and it is suggested that the major result of this approach should be the proof of the existence of galaxies of all ages within a finite volume of space.