Nuclear Moments Research Articles

Smooth trends in fermium charge radii and the impact of shell effects

The quantum-mechanical nuclear-shell structure determines the stability and limits of the existence of the heaviest nuclides with large proton numbers Z ≳ 100 (refs. 1–3). Shell effects also affect the sizes and shapes of atomic nuclei, as shown by laser spectroscopy studies in lighter nuclides4. However, experimental information on the charge radii and the nuclear moments of the heavy actinide elements, which link the heaviest naturally abundant nuclides with artificially produced superheavy elements, is sparse5. Here we present laser spectroscopy measurements along the fermium (Z = 100) isotopic chain and an extension of data in the nobelium isotopic chain (Z = 102) across a key region. Multiple production schemes and different advanced techniques were applied to determine the isotope shifts in atomic transitions, from which changes in the nuclear mean-square charge radii were extracted. A range of nuclear models based on energy density functionals reproduce well the observed smooth evolution of the nuclear size. Both the remarkable consistency of model prediction and the similarity of predictions for different isotopes suggest a transition to a regime in which shell effects have a diminished effect on the size compared with lighter nuclei.

Geant4 simulations for the [formula omitted]-ray detectors of gSPEC at GSI/FAIR

A design study for the γ-ray detector array of the gSPEC project, which aims at measuring nuclear moments at GSI/FAIR, is presented. Foreseen setups, involving DEGAS and the new gDEGAS triple cluster detectors for γ-ray spectroscopy are simulated using the Geant4 framework. The main characteristics associated to these detector assemblies with the envisaged configurations, namely the photo-peak efficiency and the angular resolution, are discussed. A new correction procedure for a better reconstruction of the time-perturbed angular distribution is proposed.

Study of the Nuclear Structure Properties in Strontium (90,92,94Sr) Isotopes Using Nuclear Shell-model Calculations

In the current research, various nuclear properties energy spectrum, reduced electromagnetic transition probabilities, nuclear moments, and the distributions of both the nuclear charge and mass density as a function of radial distance from the nucleus center (r) were computed for90,92,94Sr isotopes' using the NuShellX@MSU code. The Skyrme (SLy4) potential was utilized to compute the zirconium isotopes' wave functions with mass numbers 90, 92, and 94. By employing the Gloeckner interaction and bare G-matrix, the computed results showed good agreement with the available experimental information on the aforementioned nuclear features of all the above isotopes. Additionally, the spins and parities of energy levels were confirmed and determined in accordance with certain empirical values. Furthermore an acceptable agreement for transition strengthsB(E2;2_1^+→0_1^+ ) for 90,92,94Sr , and the dipole magnetic moment of the ground state in the90Sr isotope, was observed with the available experimental values. In these calculations, new values were predicted for the above nuclear properties, which had not been previously determined experimentally. KEYWORDS: energy spectra; gloeckner interaction; model space; nuShellX code; skyrme potential; transition strengths

Performant automatic differentiation of local coupled cluster theories: Response properties and ab initio molecular dynamics

In this work, we introduce a differentiable implementation of the local natural orbital coupled cluster (LNO-CC) method within the automatic differentiation framework of the PySCFAD package. The implementation is comprehensively tuned for enhanced performance, which enables the calculation of first-order static response properties on medium-sized molecular systems using coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. We evaluate the accuracy of our method by benchmarking it against the canonical CCSD(T) reference for nuclear gradients, dipole moments, and geometry optimizations. In addition, we demonstrate the possibility of property calculations for chemically interesting systems through the computation of bond orders and Mössbauer spectroscopy parameters for a [NiFe]-hydrogenase active site model, along with the simulation of infrared spectra via ab initio LNO-CC molecular dynamics for a protonated water hexamer.

Hyperfine interactions for small systems including transition-metal elements using self-interaction corrected density-functional theory

The interactions between the electronic magnetic moment and the nuclear spin moment, i.e., magnetic hyperfine (HF) interactions, play an important role in understanding electronic properties of magnetic systems and in realizing platforms for quantum information science applications. We investigate the HF interactions for atomic systems and small molecules, including Ti or Mn, by using Fermi–Löwdin orbital (FLO) based self-interaction corrected (SIC) density-functional theory. We calculate the Fermi contact (FC) and spin-dipole terms for the systems within the local density approximation (LDA) in the FLO-SIC method and compare them with the corresponding values without SIC within the LDA and generalized-gradient approximation (GGA), as well as experimental data. For the moderately heavy atomic systems (atomic number Z ≤ 25), we find that the mean absolute error of the FLO-SIC FC term is about 27 MHz (percentage error is 6.4%), while that of the LDA and GGA results is almost double that. Therefore, in this case, the FLO-SIC results are in better agreement with the experimental data. For the non-transition-metal molecules, the FLO-SIC FC term has the mean absolute error of 68 MHz, which is comparable to both the LDA and GGA results without SIC. For the seven transition-metal-based molecules, the FLO-SIC mean absolute error is 59 MHz, whereas the corresponding LDA and GGA errors are 101 and 82 MHz, respectively. Therefore, for the transition-metal-based molecules, the FLO-SIC FC term agrees better with experiment than the LDA and GGA results. We observe that the FC term from the FLO-SIC calculation is not necessarily larger than that from the LDA or GGA for all the considered systems due to the core spin polarization, in contrast to the expectation that SIC would increase the spin density near atomic nuclei, leading to larger FC terms.

Optical nuclear electric resonance in LiNa: selective addressing of nuclear spins through pulsed lasers

Optical nuclear electric resonance (ONER), a recently proposed protocol for nuclear spin manipulation in atomic systems via short laser pulses with MHz repetition rate, exploits the coupling between the nuclear quadrupole moment of a suitable atom and the periodic modulations of the electric field gradient generated by an optically stimulated electronic excitation. In this theory paper, we extend the scope of ONER from atomic to molecular systems and show that molecular vibrations do not interfere with our protocol. Exploring the diatomic molecule LiNa as a first benchmark system, our investigation showcases the robustness with respect to molecular vibration, and the ability to address and manipulate each of the two nuclear spins independently, simply by adjusting the repetition rate of a pulsed laser. Our findings suggest that it might be possible to shift complicated spin manipulation tasks required for quantum computing into the time domain by pulse-duration encoded laser signals.

Excitation spectrum and spin Hamiltonian of the frustrated quantum Ising magnet Pr3BWO9

We present a thorough experimental investigation on of the rare-earth based frustrated quantum antiferromagnet Pr3BWO9, a purported spin-liquid candidate on the breathing kagome lattice. This material possesses a disordered ground state with an unusual excitation spectrum involving a coexistence of sharp spin waves and broad continuum excitations. Nevertheless, we show through a combination of thermodynamic, magnetometric, and spectroscopic probes with detailed theoretical modeling that it should be understood in a completely different framework. The crystal field splits the lowest quasidoublet states into two singlets moderately coupled through frustrated superexchange, resulting in a simple effective Hamiltonian of an Ising model in a transverse magnetic field. While our neutron spectroscopy data do point to significant correlations within the kagome planes, the dominant interactions are out-of-plane, forming frustrated triangular spin-tubes through two competing ferro-antiferromagnetic bonds. The resulting ground state is a simple quantum paramagnet, where the presence of strongly hyperfine-coupled nuclear moments and weak structural disorder causes significant modifications to both thermodynamic and dynamic properties. Published by the American Physical Society 2024

Electric Field Gradient in Chiral and Tetrahedral Molecules within High-Order LRESC Formalism.

In this work, we present the electric field gradient (EFG) given by the linear response elimination of the small component (LRESC) scheme up to the 1/c4 order (c is the speed of light in vacuum) in CHFClX (X = Br, I, At) chiral molecules, together with CHF2Br and CH2FX (X = Br, I, At) tetrahedral systems. The former could be good candidates for further parity violation studies, especially when heavy atoms are surrounding. In this context, the LRESC scheme demonstrates effective applicability to large tetrahedral and chiral molecules that incorporate heavy elements, with relativistic effects playing a crucial role. The LRESC results of EFG exhibit an excellent agreement with those calculated at the four-component level, giving differences of only hundredths order in a.u. (atomic units) for the bromine nucleus and less than 0.1 a.u. for the iodine nucleus. Regarding the other nuclei, for the chiral molecules, there is a heavy atom effect on the light atom (HALA) for chlorine and fluorine atoms as the substituent halogen atom becomes heavier. Furthermore, the electronic part of the EFG for the central carbon and the fluorine nuclei presents an important dependence with the environment in the molecules under study. With accurate calculations of the EFG and tabulated nuclear quadrupole moment, the nuclear quadrupole coupling constant is obtained within the LRESC scheme, including for the first time correlation effects on the spin-dependent corrections with this methodology, providing results close to the experimental ones for Cl, Br, and I atoms. At the Hartree-Fock level, the differences are around 6% for Br and I nuclei, and at the density functional theory level with the LDA and PBE0 functionals, the differences are no more than 2%.

Exploring CP violation beyond the Standard Model and the PQ quality with electric dipole moments

In some models of physics beyond the Standard Model (SM), one of the leading low energy consequences of the model appears in the form of the chromo-electric dipole moments (CEDMs) of the gluons and light quarks. We examine if these CEDMs can be distinguished from the QCD θ-term through the experimentally measurable nuclear and atomic electric dipole moments (EDMs) in both cases with and without the Peccei-Quinn (PQ) mechanism solving the strong CP problem. We find that the nucleon EDMs show a distinctive pattern when the EDMs are dominantly induced by the light quark CEDMs without the PQ mechanism. In the presence of the PQ mechanism, the QCD θ-parameter corresponds to the vacuum value of the axion field, which might be induced either by CEDMs or by UV-originated PQ breaking other than the QCD anomaly, for instance the PQ breaking by quantum gravity effects. We find that in case with the PQ mechanism the nucleon EDMs have a similar pattern regardless of what is the dominant source of EDMs among the CEDMs and θ-term, unless there is a significant cancellation between the contributions from different sources. In contrast, some nuclei or atomic EDMs can have characteristic patterns significantly depending on the dominant source of EDMs, which may allow identifying the dominant source among the CEDMs and θ-term. Yet, discriminating the gluon CEDM from the QCD θ-parameter necessitates additional knowledge of low energy parameters induced by the gluon CEDM, which is not available at the moment. Our results imply that EDMs can reveal unambiguous sign of CEDMs while identifying the origin of the axion vacuum value, however it requires further knowledge of low energy parameters induced by the gluon CEDM.

Nuclear moments: recent developments

The author has for many years kept a watching brief on the experimental study of nuclear electro-magnetic moments. Accurate values of nuclear magnetic dipole and electric quadrupole moments are a major product and the life blood of hyperfine interaction studies and their manifold applications. This paper outlines recent changes in the type of moment measurements being undertaken and the effect of modern complex electronic configuration computation on the extracted moment values.

Reexamination of nuclear magnetic dipole and electric quadrupole moments of polonium isotopes

Reexamination of nuclear magnetic dipole and electric quadrupole moments of polonium isotopes

Temperature dependence of electric-field gradient in Zn and Cd: Replacing the T3/2 law

The existing experimental data for the temperature dependence of the nuclear quadrupole interaction in Zn and Cd have been accounted for by considering reanalyzed data for structure and vibrational amplitude as a function of temperature, in combination with density functional calculations of the electric-field gradient (EFG) variation due to the structure change. For Zn the complex EFG temperature effect, previously unexplained, can be fully reproduced, while for Cd it is shown that the apparent agreement with an earlier proposed universal temperature dependence as proportional to T3/2 is due to a combination of structural and vibrational contributions. It is demonstrated that for Zn, in particular, the resulting EFG at 0 K, including the now directly calculated shift due to zero-point vibrations, and the subsequently obtained nuclear quadrupole moments, can be considerably different when taking the present revised analysis and all experimental data into account. As an additional example also one impurity system, Ge69 in Zn, is tentatively analyzed in this context. The possible extension of the present approach to other noncubic s−p metals is envisioned. Published by the American Physical Society 2024

Exploring the properties of the VB− defect in hBN: optical spin polarization, Rabi oscillations, and coherent nuclei modulation

Optically active point defects in semiconductors have received great attention in the field of solid-state quantum technologies. Hexagonal boron nitride, with an ultra-wide band gap Eg = 6 eV, containing a negatively charged boron vacancy ( VB− ) with unique spin, optical, and coherent properties presents a new two-dimensional platform for the implementation of quantum technologies. This work establishes the value of VB− spin polarization under optical pumping with λ ext = 532 nm laser using high-frequency (ν mw = 94 GHz) electron paramagnetic resonance (EPR) spectroscopy. In optimal conditions polarization was found to be P ≈ 38.4%. Our study reveals that Rabi oscillations induced on polarized spin states persist for up to 30–40 μs, which is nearly two orders of magnitude longer than what was previously reported. Analysis of the coherent electron–nuclear interaction through the observed electron spin echo envelope modulation made it possible to detect signals from remote nitrogen and boron nuclei, and to establish a corresponding quadrupole coupling constant C q = 180 kHz related to nuclear quadrupole moment of 14N. These results have fundamental importance for understanding the spin properties of boron vacancy.

Photophysical Ion Dynamics in Hybrid Perovskite MAPbX3 (X=Br, Cl) Single Crystals

AbstractHybrid organic–inorganic perovskites (HOIPs) are promising candidates for next‐generation photovoltaic materials. However, there is a debate regarding the impact of interactions between the organic center and the surrounding inorganic cage on the solar cell's high diffusion lengths. It remains unclear whether the diffusion mechanism is consistent across various halide perovskite families and how light illumination affects carrier lifetimes. The focus is on ion kinetics of (CH3NH3)PbX3 (X = Br, Cl) perovskite halide single crystals. Muon spectroscopy (μ+SR)is employed to investigate the fluctuations and diffusion of ions via the relaxation of muon spins in local nuclear field environments. Within a temperature range of 30–340 K, ion kinetics are studied with and without white‐light illumination. The results show a temperature shift of the tetragonal‐orthorhombic phase transition on the illuminated samples, as an effect of increased organic molecule fluctuations. This relation is supported by density functional theory (DFT) calculations along the reduction of the nuclear field distribution width between the phase transitions. The analysis shows that, depending on the halide ion, the motional narrowing from H and N nuclear moments represents the molecular fluctuations. The results demonstrate the importance of the halide ion and the effect of illumination on the compound's structural stability and electronic properties.

PyBEST: Improved functionality and enhanced performance

PyBEST: Improved functionality and enhanced performance

Measurements of binding energies and electromagnetic moments of silver isotopes – A complementary benchmark of density functional theory

We report on a set of high-precision measurements of nuclear binding and excitation energies, as well as nuclear spins, magnetic dipole and electric quadrupole moments of neutron-rich silver isotopes, 113−123Ag. The measurements were performed using the JYFLTRAP mass spectrometer and the collinear laser spectroscopy beamline at the Ion Guide Isotope Separator On-Line (IGISOL) facility. For the first time, we can firmly establish the ordering of the long-lived Iπ=1/2−,7/2+ states in these isotopes, and pin down the inversion of these two levels at either A=121(N=74) or A=123(N=76). We compare these findings to calculations performed with density functional theory (DFT), from which we establish the crucial role that the spin-orbit strength and time-odd mean fields play in the simultaneous description of electromagnetic moments and nuclear binding.

High Accurate Investigation of the Nuclear Hydrodynamical Moment of Inertia

A method for investigating the non-axial moments of inertia within the framework of the hydrodynamical model is developed to give a high accurate formula of the hydrodynamical moments of inertia. In these investigations the third order of the deformation parameter is taken into account.

Electromagnetic moments of the antimony isotopes 112−133Sb

Nuclear moments of the antimony isotopes 113−133Sb are measured by collinear laser spectroscopy and used to benchmark phenomenological shell-model and ab initio calculations in the valence-space in-medium similarity renormalization group (VS-IMSRG). The shell-model calculations reproduce the electromagnetic moments over all Sb isotopes when suitable effective g-factors and charges are employed. Good agreement is achieved by VS-IMSRG for magnetic moments on the neutron-deficient side for both odd-even and odd-odd Sb isotopes while its results deviate from experiment on the neutron-rich side. When the same effective g-factors are used, VS-IMSRG agrees with experiment nearly as well as the shell model. Hence, the wave functions are very similar in both approaches and missing contributions to the M1 operator are identified as the cause of the discrepancy of VS-IMSRG with experiment. Electric quadrupole moments remain more challenging for VS-IMSRG.

Neutron star characteristics from the neutron structure

We draw insight into the neutron star structure and characteristics from the neutron structure. The eigenvectors of the special unitary group, SU(3), describing baryons, imply that neutron quarks reside on three faces of a tetrahedron. The tetrahedral structure accounts for the neutron magnetic moment and mass. Thus, we reason that neutrons precipitate with aligned magnetic moments into the triakis truncated tetrahedron tessellation under immense gravitational pressure. As the particle’s tetrahedral symmetry does not match the crystal’s rhombic symmetry, the total magnetic moment invariably misaligns with the star’s spinning axis. We infer further from the neutron structure that with increasing gravitational pressure, two neutrons condense into the same tetrahedron. Due to doubling density, the contracting star spins up abruptly but then settles down slowly as the gradients in density smoothen. As down quarks are positioned for pairwise fusions into anti-up quarks in the dineutron, we reason that tetraquark indeed forms as gravitational pressure increases further. The star balances the accompanying loss of mass by spinning down suddenly but recovers as the gradients in density smoothen again. Ultimately, when gravitational pressure increases even more, the anti-up quarks will annihilate with up quarks. As the core becomes ever more structured, such high-energy events fade out, and eventually, only magnetic field-collimated radio-frequency dissipation drives the spin down. The nuclear moments manifest fully in a magnetar, free from floating, hence counteraligning baryonic matter. In conclusion, the neutron structure makes sense of the neutron star density, magnetism, beams at an angle to the spinning axis, and pulsing transients, and paves the way for making sense of reactions in a black hole.

Variation of the Quadrupole Hyperfine Structure and Nuclear Radius due to an Interaction with Scalar and Axion Dark Matter.

Atomic spectroscopy is used to search for the space-time variation of fundamental constants which may be due to an interaction with scalar and pseudoscalar (axion) dark matter. In this Letter, we study the effects that are produced by the variation of the nuclear radius and electric quadrupole moment. The sensitivity of the electric quadrupole hyperfine structure to both the variation of the quark mass and the effects of dark matter exceeds that of the magnetic hyperfine structure by 1-2 orders of magnitude. Therefore, the measurement of the variation of the ratio of the electric quadrupole and magnetic dipole hyperfine constants is proposed. The sensitivity of the optical clock transitions in the Yb^{+} ion to the variation of the nuclear radius allows us to extract, from experimental data, limits on the variation of the hadron and quark masses, the QCD parameter θ and the interaction with axion dark matter.