Atomic Nuclei Research Articles

Nuclear moments of indium isotopes reveal abrupt change at magic number 82.

In spite of the high-density and strongly correlated nature of the atomic nucleus, experimental and theoretical evidence suggests that around particular 'magic' numbers of nucleons, nuclear properties are governed by a single unpaired nucleon1,2. A microscopic understanding of the extent of this behaviour and its evolution in neutron-rich nuclei remains an open question in nuclear physics3-5. The indium isotopes are considered a textbook example of this phenomenon6, in which the constancy of their electromagnetic properties indicated that a single unpaired proton hole can provide the identity of a complex many-nucleon system6,7. Here we present precision laser spectroscopy measurements performed to investigate the validity of this simple single-particle picture. Observation of an abrupt change in the dipole moment at N = 82 indicates that, whereas the single-particle picture indeed dominates at neutron magic number N = 82 (refs. 2,8), it does not for previously studied isotopes. To investigate the microscopic origin of these observations, our work provides a combined effort with developments in two complementary nuclear many-body methods: ab initio valence-space in-medium similarity renormalization group and density functional theory (DFT). We find that the inclusion of time-symmetry-breaking mean fields is essential for a correct description of nuclear magnetic properties, which were previously poorly constrained. These experimental and theoretical findings are key to understanding how seemingly simple single-particle phenomena naturally emerge from complex interactions among protons and neutrons.

Symplectic effective field theory for nuclear structure studies

A symplectic effective field theory that unveils the observed emergence of symplectic symmetry in atomic nuclei is advanced. Specifically, starting from a simple extension of the harmonic-oscillator Lagrangian, an effective field theory applied against symplectic basis states is shown to yield a Hamiltonian system with one fitted parameter. The scale of the system can be determined self-consistently as the ratio of the average volume of a nucleus assumed to be spherical to its volume as determined by the average number of oscillator quanta, which is stretched by the fact that the plane-wave solution satisfies the equations of motion at every order without the need for perturbative corrections. As an application of the theory, results for $^{20}\mathrm{Ne}$, $^{22}\mathrm{Ne}$, and $^{22}\mathrm{Mg}$ are presented that yield energy spectra, $B(E2)$ values, and matter radii in good agreement with experimentally measured results.

Statistical correlations of nuclear quadrupole deformations and charge radii

Shape deformations and charge radii, basic properties of atomic nuclei, are influenced by both the global features of the nuclear force and the nucleonic shell structure. As functions of proton and neutron number, both quantities show regular patterns and, for nuclei away from magic numbers, they change very smoothly from nucleus to nucleus. In this paper, we explain how the local shell effects are impacting the statistical correlations between quadrupole deformations and charge radii in well-deformed even-even Er, Yb, and Hf isotopes. This implies, in turn, that sudden changes in correlations can be useful indicators of underlying shell effects. Our theoretical analysis is performed in the framework of self-consistent mean-field theory using quantified energy density functionals and density-dependent pairing forces. The statistical analysis is carried out by means of the linear least-square regression. The local variations of nuclear quadrupole deformations and charge radii, explained in terms of occupations individual deformed Hartree-Fock orbits, make and imprint on statistical correlations of computed observables. While the calculated deformations or charge radii are, in some cases, correlated with those of their even-even neighbors, the correlations seem to deteriorate rapidly with particle number. The statistical correlations between nuclear deformations and charge radii of different nuclei are affected by the underlying shell structure. Even for well deformed and superfluid nuclei for which these observables change smoothly, the correlation range usually does not exceed $\Delta N=4$ and $\Delta Z=4$, i.e., it is rather short. This result suggests that the frequently made assumption of reduced statistical errors for the differences between smoothly-varying observables cannot be generally justified.

Measurements of proton beam attenuation radiographs at a clinical facility

In recent years, a proton computed tomography (pCT) demonstrator was installed and tested at the MedAustron facility in Wiener Neustadt, Austria. It consists of four double-sided silicon strip detectors (DSSDs) for particle tracking and a range telescope to obtain the residual range of the protons that passed through the object to be imaged. Besides conventional pCT, which uses the energy loss information of the single ions, the tracker of the demonstrator also allows for other imaging modalities such as beam attenuation imaging (also referred to as fluence loss imaging). When a proton beam passes through a medium, a certain fraction of the incident primary particles gets absorbed due to the inelastic scattering with the atomic nuclei of the material. Recent studies investigating proton imaging based on inelastic nuclear scattering at clinical energies with single-particle tracking used Monte Carlo simulations and lack additional experimental validation. In this work, proton radiographs based on beam attenuation were measured at clinical beam energies (100.4 MeV, 145.4 MeV) and, for the first time, at 800 MeV. As phantom, an aluminum stair profile was imaged at two different rotation angles to investigate material thicknesses between 2 mm and 10 mm. The recorded beam attenuation was compared to existing reference data from prior measurements and the inelastic nuclear cross sections as incorporated in the Geant4 database. Furthermore, the measurement at 800MeV could be compared to an existing measurement of the inelastic nuclear cross section of aluminum at a similar energy (792.9 MeV).

Bohr Hamiltonian with Hulthen plus screened Kratzer potential using super symmetric quantum mechanics

In this paper, we look for a novel analytical solution of the Bohr Hamiltonian in the presence of the Hulthen plus screened Kratzer potential in [Formula: see text]-part of the collective nuclear potential. The new expression for the energy spectra is obtained using the method of super symmetric quantum mechanics. The effect of the Hulthen plus screened Kratzer potential is studied on root mean square deviation, and normalized eigen energies of ground state band, [Formula: see text]-band and [Formula: see text]-band of 192Pt, 194Pt and 196Pt atomic nuclei. The [Formula: see text] transition rates are calculated for the latter potential. Furthermore, our results are compared with experimental data, and other relevant theoretical works. We discuss on how the combination of these two potentials makes it possible to improve the results of energy spectra and quadrupole transitions of triaxial nuclei. We discuss the quantitative and qualitative descriptions concerning the structure of the nucleus using some indicators such as root mean square and staggering of the [Formula: see text]-band. The results provided by our model are found to be in good agreement with experimental data and improved in comparison with previous works.

КОМПЬЮТЕРНАЯ ВИЗУАЛИЗАЦИЯ ПРОСТРАНСТВЕННОЙ СТРУКТУРЫ АТОМНОГО ЯДРА

Based on the model of the nuclear shells, a computer model of the spatial structure of the atomic nucleus was constructed. The application of the new approach, by analogy with the modeling of the atom electron shell, allowed us to visualize the structure of the atomic nucleus. In the presented spatial model, the concept of nucleon is also extended to include, besides protons and neutrons, deuterons in the nuclear shell. The nature of quantum and magic numbers is clarified, and the structure of the nuclear shell is shown. The resulting spatial arrangement of nucleons clearly shows the presence of a fine structure in the nucleus. Adequacy of the model is confirmed by correlations of the dependences of the nucleus radius on the charge number, as well as by the curve of the asymmetric nucleus shape dependence on the charge number which almost entirely coincides with a similar dependence of the electric quadrupole moment. The reasons for limiting the number of isotopes existing in nature have been considered. Based on the results obtained, equations for estimating the limiting number of isotopes in atoms for the NP-diagram have been determined.

Stability of Spherical Nuclei in the Inner Crust of Neutron Stars

Neutron stars are the densest objects in the Universe. In this paper, we consider the so-called inner crust—the layer where neutron-excess nuclei are immersed in the degenerate gas of electrons and a sea of quasi-free neutrons. It was generally believed that spherical nuclei become unstable with respect to quadrupole deformations at high densities, and here, we consider this instability. Within the perturbative approach, we show that spherical nuclei with equilibrium number density are, in fact, stable with respect to infinitesimal quadrupole deformation. This is due to the background of degenerate electrons and associated electrostatic potential, which maintain stability of spherical nuclei. However, if the number of atomic nuclei per unit volume is much less than the equilibrium value, instability can arise. To avoid confusion, we stress that our results are limited to infinitesimal deformations and do not guarantee strict thermodynamic stability of spherical nuclei. In particular, they do not exclude that substantially non-spherical nuclei (so-called pasta phase) represent a thermodynamic equilibrium state of the densest layers of the neutron star crust. Rather, our results point out that spherical nuclei can be metastable even if they are not energetically favourable, and the timescale of transformation of spherical nuclei to the pasta phases should be estimated subsequently.

Sensitivity of Parity-Violating Electron Scattering to a Dark Photon.

We explore the sensitivity of the parity-violating electron scattering (PVES) asymmetry in both elastic and deep-inelastic scattering to the properties of a dark photon. Given advances in experimental capabilities in recent years, there are interesting regions of parameter space where PVES offers the chance to discover new physics in the near future. There are also cases where the existence of a dark photon could significantly alter our understanding of the structure of atomic nuclei and neutron stars as well as parton distribution functions.

Functional Materials for Fusion Nuclear Power Cores (A Technical Memorandum)

Nuclear energy science is nothing new, since World War II (WW II) and the successful Manhattan Project started in the deserts of New Mexico around 1940’s with Fermi introducing his experimental fission reactor in basement of University of Chicago in state of Illinois. Following that project and the exploring application of atom energy for peaceful goals using famous Einstein’s theory E=mc^2 has turned a new chapter for nuclear power energy by introducing a new source for electricity production. Fusion nuclear power generation that totally works in opposite direction that of fission nuclear power by splitting atoms nuclei of high Z-materials such as Uranium (U) or Plutonium (Pu), it uses the technology of thermonuclear reaction concepts driven by two isotopes of Hydrogen elements mainly Deuterium (D) and Tritium (T). Recent progress in research towards the development of fusion power driven by means of magnetic confinement approach, using reactor such as Tokamak device and the impressive advances research made in this particular reactor in the past few years, seems very promising to strike break-even of thermonuclear driven fusion reaction taking into consideration approach of Magnetic Confinement Fusion (MCF). Tokamak devices currently under construction will demonstrate the break-even condition or scientific feasibility of fusion power. Exciting and innovative ideas in mirror magnetic confinement are expected to culminate in high-Q devices making open-ended confinement a serious contender for fusion reactors. However, with such an innovative approach comes its own technical challenges associated with the machinery such as Tokamak that internally requires in a harsh temperature that in nature can be seen at the surface of our Sun, thus we are in need of materials that can sustain such high-temperature heat and be able to maintain their integrity and extend the life-cycle of such device while in full commercial operation within period of 24x7x360. Here in this Technical Memorandum (TM), we discuss potential materials that are possibly can deliver such sustainability one need them to operate within high-temperature and maintain their both physical and chemical properties from physics of solid-states point of view. With also today’s research in Nanotechnology and Memory-metals reaching to such a goal seems to be achievable, which is subject of this Technical Memorandum (TM)

Mass-area equivalence in classical physics and aspects of mutual shielding of objects

The physical and mathematical aspects of the mutual spatial shielding of interacting elements in the framework of classical physics are considered. The mass-area equivalence is introduced for the formal unification of the Newtonian theory of gravity with the kinetic theories of Descartes-Fatio-Le Sage. A mathematical equation describing the dependence of the mutual shielding of objects on their size, number and relative location is proposed. Spatial mutual shielding is considered for mass-forming elements—nucleons in the atomic nucleus and atomic nuclei in ordinary substances. The close shielding is distinguished when the distance between the shielding elements is commensurate with their size, which is typical for nucleons in atomic nuclei and the far shielding, when the distance between the elements is much larger than their size, which is typical for atomic nuclei in ordinary substances. An analytical expression for the binding energy of nucleons in atomic nucleus is obtained. It allows us to estimate the distance between nucleons in the nucleus and consider stability of nuclei as a function of the distance between nucleons, which increases due to an increase in the Coulomb repulsion force with an increase in the number of protons. One of the three ideas of Dirac, presented by him for the further development of the physical theory, is implemented: taking into account the sizes of elementary particles—nucleons.

The meanings of the mysterious number 137

The fine-structure constant inverse is 1/α ≅ 137.036. Both the Nobel Prize winners, Pauli and Feynman, became fascinated by the number 137; anyhow, physicists have not yet found any relation between such number and any other physical law. Here the integer 137 has several clear meanings, on the bases of the following two premises: 1) Form of light: longitudinal massive particles (photons) having length λ=c/v with v their frequency, namely the number of photons, of the same ray (continuous succession of photons), crossing a given observer in a time unit. 2) Electron structure: its charge is not uniformly distributed, but it can be considered as a point particle fixed on the electron spherical surface and facing the atom nucleus during the electron orbits; the electron charge also corresponds to the photons-electron impact point, where photons are absorbed and released. On the above bases, on H atom we found the following main results: n = 1, 2, ..137 electron different circular orbits with n2 the number of admitted photons along two equal circular orbits; v=αc electron charge ground-state (g-s) orbital speed; r= α/4πRH electron charge g-s orbit, with RH the Rydberg constant; v = c/137 exact, electron g-s orbital speed. As for the claimed fall of circling electrons into their nucleus due to their supposed photons emission, we found that the electrons are emitting the previously absorbed photons only during their spiral path toward lower orbits.

Gravitational wave signal recognition and ring-down time estimation via Artificial Neural Networks

Laser Interferometer Gravitational-Wave Observatory (LIGO) was the first laboratory to measure the gravitational waves successfully. An exceptional experimental design was needed to measure distance changes less than an atomic nucleus. In the same way, the data analyses to confirm and extract information is a tremendously challenging task. This article shows a computational procedure based on Artificial Neural Networks (ANN) to recognize a black hole-black hole gravitation wave event signal from the LIGO data. With the ANN introduced methodology, it is possible to define a numerical score, like a thermometer. High score values are associated with gravitational wave observation and small values with noise. Building a time series from these scores values, physical information about the astronomical system’s damping time, the ring-down time, can be estimated at a first approximation, based on a damped harmonic oscillator modeling. Here, the ring-down time is estimated, at a first approximation, with a direct data measure on the ANN score time series, without using numerical relativity techniques and high computational power.

Symmetry breaking of Gamow-Teller and magnetic-dipole transitions and its restoration in calcium isotopes

Nuclear magnetic-dipole (M1) and Gamow-Teller (GT) transitions provide insight into the spin-isospin properties of atomic nuclei. By considering them as unified spin-isospin transitions, the M1/GT transition strengths and excitation energies are subject to isospin symmetry. The excitation properties associated to the M1/GT symmetry need to be clarified within consistent theoretical approach. In this work, the relationship between the M1 and GT transitions in Ca isotopes is investigated in a unified framework based on the relativistic energy-density functional (REDF) with point-coupling interactions, using the relativistic quasi-particle random-phase approximation (RQRPA). It is shown that the isovector-pseudovector (IV-PV) residual interaction affects both transitions, and the symmetry of M1 and giant-GT transitions is disrupted by this interaction in closed-shell nuclei. In open-shell Ca isotopes, the proton-neutron pairing in the residual RQRPA interaction also plays a role in GT transitions. Due to the interplay between these interactions, the M1/GT symmetry can be restored especially in the $^{42}$Ca nucleus, i.e., the giant-GT strength can become comparable to that of the M1 mode in terms of the unified spin-isospin transitions by adjusting the PN-pairing strength to reproduce the experimental low-lying GT-excitation energies. The mirror symmetry of both M1 and GT transitions is also demonstrated for open-shell mirror partners, $^{42}$Ca and $^{42}$Ti. Further improvements are required to achieve simultaneous reproduction of M1 and GT-transition energies in the REDF framework.

A Hartree-Fock-Bogoliubov Study on the Pairing Correlations of the Isotopes of Cobalt

Background: The phenomena of nucleon pairing could be outlined from the Bethe-Weizäcker semi-empirical formula, from which the nuclear properties, viz. the binding energy, stability, shape etc. could be clearly sketched. Though the pairing correlation seems to be a small correction to the binding energy term, it plays a determinative role in defining the structure of nuclear systems. The addition to the binding energy in turn affects the position of the isotope on the dripline and hence increases the stability.
 Purpose: To study the effects of pairing on the ground state properties of the isotopes of Cobalt.
 Methods: We use Hartree-Fock-Bogoliubov (HFB) theory for the study. The general wave functions for the HFB approach are determined from variational principle. The eigen functions for the Hamiltonian are connected with the particle operators through the Bogoliubov transformations. The Hartree-Fock energy is obtained through the minimization of the variational parameter and the HFB equation is solved by iterative diagonalization by restoring the particle number symmetry.
 Results: The HFB analysis substantiates the effect of pairing correlation on binding energies, neutron and proton pairing energies, neutron and proton pairing gaps and one- and two-neutron separation energies of the Cobalt isotopes. The binding energies and one and two-neutron separation energies match with the experimental values and for pairing energies and pairing gaps, the regions where pairing is significant and the effects of shell closure at the vicinity of magic configuration of neutrons could be recognized.
 Conclusion: The Hartree-Fock-Bogoliubov calculations of the effects of pairing could be used as an efficient tool to study the nuclear structure. It can be ascertained that pairing plays an important role in determining the ground state properties of atomic nuclei.

Simultaneous Estimation of Two Coupled Hydrogen Bond Geometries from Pairs of Entangled NMR Parameters: The Test Case of 4-Hydroxypyridine Anion.

The computational method for estimating the geometry of two coupled hydrogen bonds with geometries close to linear using a pair of spectral NMR parameters was proposed. The method was developed based on the quantum-chemical investigation of 61 complexes with two hydrogen bonds formed by oxygen and nitrogen atoms of the 4-hydroxypyridine anion with OH groups of substituted methanols. The main idea of the method is as follows: from the NMR chemical shifts of nuclei of atoms forming the 4-hydroxylpyridine anion, we select such pairs, whose values can be used for simultaneous determination of the geometry of two hydrogen bonds, despite the fact that every NMR parameter is sensitive to the geometry of each of the hydrogen bonds. For these parameters, two-dimensional maps of dependencies of NMR chemical shifts on interatomic distances in two hydrogen bonds were constructed. It is shown that, in addition to chemical shifts of the nitrogen atom and quaternary carbon, which are experimentally difficult to obtain, chemical shifts of the carbons and protons of the CH groups can be used. The performance of the proposed method was evaluated computationally as well on three additional complexes with substituted alcohols. It was found that, for all considered cases, hydrogen bond geometries estimated using two-dimensional correlations differed from those directly calculated by quantum-chemical methods by not more than 0.04 Å.

S -wave pion condensation in symmetric nuclear matter

S-wave pion-nucleon interactions in the linear sigma model, and in Manohar-Georgi and Gasser-Sainio-Svarc models with finite number of terms in Lagrangians, as well as in a general phenomenological approach are reviewed. Subtleties associated with the current algebra theorems and field redefinitions are discussed. In the first and third models most likely the s-wave pion condensation in the isospin-symmetric matter does not occur at least up to high densities, whereas within the second model it may appear already at moderate densities. In the phenomenological approach two parameterizations of the s-wave pion-nucleon scattering amplitude and the pion polarization operator used in the literature are considered. The first parameterization employs the off-mass-shell amplitude and allows to fulfil the current algebra theorems. Using it the s-wave pion polarization operator in the isospin-symmetric matter is reconstructed within the gas approximation. With this pion polarization operator the s-wave pion condensation in the isospin-symmetric matter does not occur at least up to high densities. Second parameterization uses the on-mass-shell pion-nucleon scattering amplitude and does not satisfy the Adler and Weinberg conditions. With such a parameterization most likely the s-wave pion condensation in the isospin-symmetric matter may occur already at the nucleon density $n\simeq (1.4-2.5) n_0$, where $n_0$ is the density of the atomic nucleus, that should result in observable effects. Both parameterizations allow to successfully describe the pion atom data.

Inelastic Dirac dark matter

Feebly interacting thermal relics are promising dark matter candidates. Among them, scenarios of inelastic Dark Matter evade direct detection by suppressed elastic scattering off atomic nuclei. We introduce inelastic Dirac Dark Matter, a new model with two Dirac fermions in the MeV-GeV mass range. At feeble couplings, dark matter can depart from chemical as well as kinetic equilibrium with the Standard Model before freeze-out. In this case, the freeze-out is driven by conversion processes like coscattering, rather than coannihilation. We show that inelastic Dirac relics are consistent with cosmological observations, in particular with nucleosynthesis and the cosmic microwave background. Searches for dark sectors at colliders and fixed-target experiments, in turn, are very sensitive probes. Compared to the strongly constrained pseudo-Dirac scenario, inelastic Dirac Dark Matter offers a new search target for existing and upcoming experiments like Belle II, ICARUS, LDMX and SeaQuest.

Dual tuned 1H/31P quadrature microstripline-based transmit/receive switch for 7 Tesla magnetic resonance imaging

<p><span>A dual tuned transmit/receive (T/R) Switch for 7 tesla magnetic resonance imaging</span> (MRI) that is based on concentric microstripline (MSL) coupler is introduced. The proposed switch is designed using two concentric MSL quadrature couplers on the top and bottom faces of the switch. The switch can be used to handle two frequency signals to/from two radio frequency (RF) coils. In this article, a 1H/31P atomic nuclei are excited. The two MSLs on the upper face of the switch are designed to transmit 298 and 120.6 MHz signals into RF coils, whereas each of the identical upper and lower MSLs are used to receive these signals from the RF coils. This switch can be used to transmit/receive signals from two RF coils at the same time, one work with 1H and the second with 31P atomic nuclei, and without any tuning. The proposed switch has been designed and simulated using the electromagnetic microwave studio computer simulation technology (CST). It demonstrates good matching (≈17 dB), low insertion loss (≈0.3) and high isolation (>70) for the 1H and 31P magnetic resonance signals at transmit mode. During receive mode, It demonstrates good matching (>20 dB), low insertion loss (≈0.2) and high isolation (>70) for the 1H and 31P magnetic resonance signals.</p>

Modification of the SVD Unfolding Regularization Method

Unfolding is currently an important stage of processing experimental data, reducing the effect of errors and reconstructing approximately real distributions of quantities. Numerous approaches exist to solve this problem; in particular, they are widely used in the modern physics of atomic nuclei and elementary particles, space physics, and other related areas. However, many algorithms are not designed or are poorly adapted to reconstruct multidimensional distributions corresponding to, e.g., several characteristics of particles measured simultaneously. In this work, a method has been proposed to adapt the singular value decomposition (SVD) unfolding algorithm to the multidimensional case. The proposed modified method has been tested in application to simulation data for the cosmic ray spectrum measured in the PAMELA space experiment. This method not only makes it possible to estimate the real distribution of a multidimensional quantity (momentum and two angles specifying the direction of entering a particle into an instrument) but also provides a better result compared to the classical SVD approach in the one-dimensional case (only the momentum of the p-article).

Spectral density reconstruction with Chebyshev polynomials

Accurate calculations of the spectral density in a strongly correlated quantum many-body system are of fundamental importance to study its dynamics in the linear response regime. Typical examples are the calculation of inclusive and semiexclusive scattering cross sectionsin atomic nuclei and transport properties of nuclear and neutron star matter. Integral transform techniques play an important role in accessing the spectral density in a variety of nuclear systems. However, their accuracy is in practice limited by the need to perform a numerical inversion which is often ill-conditioned. In the present work we extend a recently proposed quantum algorithm which circumvents this problem. We show how to perform controllable reconstructions of the spectral density over a finite energy resolution with rigorous error estimates. An appropriate expansion in Chebyshev polynomials allows for efficient simulations also on classical computers. We apply our idea to obtain the local density of states for graphene in a magnetic field as a proof of principle. This paves the way for future applications in nuclear and condensed matter physics.