Single-particle Configurations Research Articles

Band terminations and maximum spin values with up to 18 aligned particles (and holes) in the Z,N=50 to 82 shells

Observed rotational bands that terminate or appear to terminate at very high spin are analyzed within the configuration constrained cranked Nilsson-Strutinsky (unpaired CNS or CNSB with pairing) formalism. Spin values for the nuclei discussed reach or come close to the maximum spin that can be built within the Z,N=50–82 shells. Configurations are distinguished not only by the number of particles in high-j and low-j shells within each N shell but, in some cases, also by the number of particles in pseudospin partners like d5/2g7/2 and s1/2d3/2. Configurations in Dy156 and Hf164, which terminate at I≈60, are well understood in terms of their occupation of open j shells or groups of j shells. The bands in Dy156 are tentatively observed up to termination while the bands in Hf164 are still a few spin units away. These terminating states are built with up to 18 aligned particles or 18 particles+holes outside a core. The core is built from nucleons in filled j shells, which gives no contribution to the spin. Analysis of the high-spin bands in Xe125,126 and Ce131,132 suggests that bands in Xe126 and Ce132 are observed to terminate at similar spin values, where terminating bands in Xe126 are observed high above yrast. It is remarkable that the deformed mean field, plus single-particle configurations, is able to provide such a comprehensive description of known experimental levels in nuclei up to spin 60ℏ and beyond. It is also impressive that the model can relate alignments of single-particle spin vectors to changes in shape with the nuclear spin. Published by the American Physical Society 2024

Investigating the level structure of 206Rn: evolution from seniority regime to collective dynamics* *Supported partially by the National Natural Science Foundation of China(10975191, U1867210, 11375023, 11475014, 11575018, 12075169 , 12322506), and the National Key R&D program of China (2016YFA0400504)

Excited states of have been examined via the ( , 5n) fusion reaction at a beam energy of 78 MeV. A number of transitions and levels are identified by the γ-γ coincidence measurement, further enriching the level scheme of . The full configuration shell model and nucleon-pair approximation (NPA) were utilized to investigate the single-particle configurations and seniority structures in . The results of these two calculations suggest that and states exhibit only a 50% component of a seniority-two state associated with a broken neutron pair. The collectivity of these two states primarily arises from configuration mixing due to residual proton-neutron interactions. Furthermore, and states are predominantly characterized by a seniority-two state marked by a broken proton pair.

Enhancing particle string detection in electrorheological plasmas using asymmetrical kernel convolutional networks

Under different plasma conditions and electric fields in a complex plasma the plasma particles organize themselves in a string-like or chain-like manner. A phase transition from string-like to an isotropic particle distribution is observed at different electrical conditions. The streaming of charged ions around plasma particles with the surrounding electric field gives the plasma its electrorheological properties. The visibility of individual particles in a complex plasma opens up the opportunity to examine properties and phase transitions of such electrorheological fluids in detail. Because of the limited one-dimensional symmetry, determining the configuration of a particle and recognizing strings in particle distributions is not always straightforward. Several approaches have already been used to analyse particle clouds while either considering each particle locally or considering the particle cloud as a whole without providing information about single particle configurations. This paper presents a new machine learning approach that takes advantage of particle distributions over the entire particle cloud and detects all string-like particles at once, using a convolutional neural network in form of an encoder-decoder network with asymmetric kernel convolutions. This not only enhances the result quality but also accelerates the evaluation process, possibly enabling real-time analyses on electrorheological phase transitions, while achieving an accuracy of over 95% on manually labelled data.

Ne21 energy levels approaching the α -particle threshold

Nuclei around Ne20 exhibit an interplay of different excitations caused by different aspects of nuclear structure, including single-particle and multiparticle configurations and collective rotations. One-nucleon transfer reactions selectively probe single-particle structures in these nuclei. These nuclei are also important to astrophysics, with a number of important reactions proceeding through this mass region. Energy levels approaching the α-particle threshold in Ne21 are of importance to nuclear structure. The Ne20(d,p)Ne21 reaction was measured and the corresponding spectroscopic nuclear information was extracted. States in Ne21 were populated using the Ne20(d,p)Ne21 reaction in forward kinematics. Protons were identified in the Triangle Universities Nuclear Laboratory (TUNL) Enge split-pole spectrograph and angular distributions were extracted. Spin-party assignments were made and neutron partial widths were determined based on distorted-wave Born approximation (DWBA) analysis. Several new energy levels were observed at energies of 7176, 7235, 7250, and 7337 keV, and spin-parities are reported which generally agree with previous results where literature was available. Spin and parity assignments are reported for several energy levels along with estimated neutron widths for those states above the neutron threshold (Sn=6761keV). Results from this study are placed in context with a review of the available literature on all known states in this energy region of Ne21.Published by the American Physical Society2024

Study of the one-neutron transfer reaction in 18O + 76Se collision at 275 MeV in the context of the NUMEN project

Heavy-ion one-nucleon transfer reactions are promising tools to investigate single-particle configurations in nuclear states, with and without the excitation of the core degrees of freedom. An accurate determination of the spectroscopic amplitudes of these configurations is essential for the study of other direct reactions as well as beta-decays. In this context, the 76Se(18O,17O)77Se one-neutron transfer reaction gives a quantitative access to the relevant single particle orbitals and core polarization transitions built on 76Se. This is particularly relevant, since it provides data-driven information to constrain nuclear structure models for the 76Se nucleus.The excitation energy spectrum and the differential cross section angular distributions of this nucleon transfer reaction was measured at 275 MeV incident energy for the first time using the MAGNEX large acceptance magnetic spectrometer. The data are compared with calculations based on distorted wave Born approximation and coupled channel Born approximation adopting spectroscopic amplitudes for the projectile and target overlaps derived by large-scale shell model calculations and interacting boson-fermion model.These reactions are studied in the frame of the NUMEN project. The NUMEN (NUclear Matrix Elements for Neutrinoless double beta decay) project was conceived at the Istituto Nazionale di Fisica Nucleare–Laboratori Nazionali del Sud (INFN-LNS) in Catania, Italy, aiming at accessing information about the nuclear matrix elements (NME) of neutrinoless double beta decay (0νββ) through the study of the heavy-ion induced double charge exchange (DCE) reactions on various 0νββ decay candidate targets. Among these, the 76Se nucleus is under investigation since it is the daughter nucleus of 76Ge in the 0νββ decay process.

Giant dipole resonance and its fine structures in 144−152Nd,152Sm studied within the linear response theory

We present a microscopic approach for giant dipole resonance (GDR) where the linear response by the nuclear density to the dipole radiation is represented through the single-particle wavefunctions calculated with a triaxial Woods-Saxon potential. We follow a microscopic-macroscopic approach to estimate the nuclear deformation with the same potential. We explain the recent experimental data for even–even nuclei 144−152Nd and 152Sm and present a comparison with the macroscopic approach for GDR. We highlight the cases where the results from the microscopic approach are sensitive to the change in single-particle configuration despite no change in shape and mass but with a change of two protons in a mid-shell region. We also present the fine structure analysis of the GDR cross-section using the continuous wavelet transform (CWT) framework and elucidate the origin of such fine structures.

Single-particle configurations of the excited states of Po203

Excited states of the $^{203}$Po ($Z = 84, N = 119$) have been investigated after populating them through $^{194}$Pt($^{13}$C,4n) fusion-evaporation reaction at E$_{beam}$ = 74 MeV and using a large array of Compton suppressed HPGe clover detectors as the detection setup for the emitted $\gamma$-rays. Standard techniques of $\gamma$-ray spectroscopy have been applied towards establishing the level structure of the nucleus. Twenty new $\gamma$-ray transitions have been identified therein, through $\gamma-\gamma$ coincidence measurements, and spin-parity assignments of several states have been determined or confirmed, following the angular correlation and linear polarization measurements on the observed $\gamma$-rays. The excited states have been interpreted in the framework of large basis shell model calculations, while comparing their calculated and experimental energies. They have been principally ascribed to proton population in the $h_{9/2}$ and $i_{13/2}$ orbitals outside the $Z = 82$ closure and neutron occupation of the $f_{5/2}$, $p_{3/2}$ and $i_{13/2}$ orbitals in the $N = 126$ shell.

Single-particle and cluster modes of 13C excited states of 3.09, 8.86 and 9.89MeV

The elastic and inelastic scatterings of deuterons from [Formula: see text]C are registered in a wide range of angles at the laboratory energy of 14.5[Formula: see text]MeV. Data on the differential cross-sections are treated within both the optical model and coupled-channels method. A new set of optical potential parameters is found. Analyses of the [Formula: see text] nuclear reactions are carried out for the levels of excitation 3.089, 8.86 and 9.87[Formula: see text]MeV. The single particle [Formula: see text], and cluster [Formula: see text] models are applied in calculations of differential cross-sections. The calculations show that the state 3.089[Formula: see text]MeV is populated with the single particle configuration, while the latter bands 8.86[Formula: see text]MeV and 9.87[Formula: see text]MeV mainly have the cluster [Formula: see text] excitation. The major contribution of the Hoyle state of the core [Formula: see text] is not observed, but the cluster [Formula: see text] configuration is ascertained to be the main contributor to the state 8.86[Formula: see text]MeV.

Fission properties of Rf253 and the stability of neutron-deficient Rf isotopes

An analysis of recent experimental data [J. Khuyagbaatar et al., Phys. Rev. C 104, L031303 (2021)] has established the existence of two fissioning states in $^{253}$Rf: the ground state and a low-lying isomeric state, most likely involving the same neutron single-particle configurations as in the lighter isotone $^{251}$No. The ratio of fission half-lives measured in $^{253}$Rf was used to predict the fission properties of the 1/2$^{+}$ isomeric state in $^{251}$No and draw conclusions as to the stability against fission of even lighter Rf systems. This paper focusses again on the fission properties of $^{253}$Rf and their impact on the stability of other neutron deficient isotopes, using new and improved data collected from two experiments performed at the Flerov Laboratory of Nuclear Reactions in Dubna, Russia. Two fission activities with half-lives of 52.8(4.4)$~\mu$s and 9.9(1.2) ms were measured in the case of $^{253}$Rf, confirming the results of J. Kkuyagbaatar et al. A third state, at much higher excitation energy, was also observed through the detection of its electromagnetic decay to the 52.8$~\mu$s state. This observation leads to the opposite quantum-configuration assignments for the fissioning states as compared to the ones established by J. Khuyagbaatar et al., namely that the higher-spin state has the shortest fission half-life. This inversion of the ratio of fission hindrances between the low and high-spin states is corroborated in the isotone $^{251}$No by the non observation of any substantial fission branch from the low-spin isomer.

Detailed modeling of aluminum particle combustion – From single particles to cloud combustion in Bunsen flames

A numerical model for aluminum cloud combustion which includes the effects of interphase heat transfer, phase change, heterogeneous surface reactions, homogeneous combustion, oxide cap growth and radiation within the Euler–Lagrange framework is proposed. The model is validated in single particle configurations with varying particle diameters. The combustion process of a single aluminum particle is analyzed in detail and the particle consumption rates as well as the heat release rates due to the various physical/chemical sub-models are presented. The combustion time of single aluminum particles predicted by the model are in very good agreement with empirical correlations for particles with diameters larger than 10 μm. The prediction error for smaller particles is noticeably reduced when using a heat transfer model that is capable of capturing the transition regime between continuum mechanics and molecular dynamics. The predictive capabilities of the proposed model framework are further evaluated by simulating the aluminum/air Bunsen flames of McGill University for the first time. Results show that the predicted temperature distribution of the flame is consistent with the experimental data and the double-front structure of the Bunsen flame is reproduced well. The burning rates of aluminum in both single particle and particle cloud configurations are calculated and compared with empirical correlations. Results show that the burning rates obtained from the present model are more reasonable, while the correlations, when embedded in the Euler–Lagrange context, tend to underestimate the burning rate in the combustion stage, particularly for the considered fuel-rich flames.

Rare-event properties in a classical stochastic model describing the evolution of random unitary circuits.

We investigate the statistics of selected rare events in a (1+1)-dimensional (classical) stochastic growth model which describes the evolution of (quantum) random unitary circuits. In such classical formulation, particles are created and/or annihilated at each step of the evolution process, according to rules which generally favor a growing cluster size. We apply a large-deviation approach based on biased Monte Carlo simulations, with suitable adaptations, to evaluate (a) the probability of ending up with a single particle at a specified final time t_{f} and (b) the probability of having particles outside the light cone, defined by a "butterfly velocity" v_{B}, at t_{f}. Morphological features of single-particle final configurations are discussed, in connection with whether the location of such particle is inside or outside the light cone; we find that joint occurrence of both events of types (a) and (b) drives significant changes to such features, signaling a second-order phase transition.

Numerical investigation and assessment of flamelet-based models for the prediction of pulverized solid fuel homogeneous ignition and combustion

The homogeneous ignition and volatile combustion of pulverized solid fuel in single-particle and particle group configurations were studied numerically in a laminar flat flame burner. Simulations with increasing particle streams were performed to investigate the influence of the interactions in particle groups on homogeneous ignition and combustion. An extensive set of simulations are conducted considering models with different levels of detail for both the gas-phase and solid fuel chemistry. The reference simulations employ the chemical percolation devolatilization model coupled with a detailed chemistry model for gas-phase reactions. The particle-fluid interactions were modeled with a fully coupled Eulerian-Lagrangian framework. Increased ignition delay times for higher particle streams were successfully validated against available experimental measurements. Furthermore, the transition from single-particle ignition to a conically shaped volatile flame with suppressed reactions near the flame base in particle group combustion was observed in both experiments and simulations. The subsequent detailed investigations revealed that the increased heat transfer to particles and, therefore, lower gas temperature for higher particle number densities together with the local oxygen depletion are the primary reasons for this transition. Based on the reference simulation, different simplified model combinations were assessed. The systematic model reduction investigation started with assessing the fixed volatile composition as a required assumption for flamelet models. Finally, the effects of gas-phase chemistry and different simple devolatilization models on ignition and combustion chemistry were studied. Overall, all model combinations provide reasonable predictions of volatile combustion with minor local deficits in the studied conditions.

Cranking covariant density functional theory with a shell-model-like approach for the superdeformed band of 42Ca

The superdeformed rotational band in 42Ca is studied with the cranking covariant density functional theory complemented by a shell-model-like approach for treating the pairing correlations. The microscopic and self-consistent description of the superdeformed rotational band is obtained. The calculated energy surfaces show local minimums at [Formula: see text] from rotational frequency [Formula: see text] [Formula: see text] to [Formula: see text][Formula: see text]MeV. The shape coexistence of spherical, normal deformation and superdeformation is found at [Formula: see text][Formula: see text]MeV. The single-particle levels and configurations are analyzed in details with the deformation. The configuration of the superdeformed band is figured out as [Formula: see text]. The single-particle Routhians indicate that the neutrons configuration plays a key role in the formation of the superdeformed band, and the change of the protons configuration at [Formula: see text][Formula: see text]MeV terminates the superdeformed band. The importance of pairing correlation to the superdeformed band is also studied in terms of the moments of inertia and the angular momentum.

Behavior of chiral bands in Cs128,130 and La130

The nonadiabatic quasiparticle approach is applied to study chiral doublet bands in $^{128}\mathrm{Cs}, ^{130}\mathrm{Cs}$, and $^{130}\mathrm{La}$. The calculated energy spectra and electromagnetic transition probabilities reproduce quite well the experimental data. $^{130}\mathrm{Cs}$ turns out to be a better example for chiral symmetry breaking than $^{128}\mathrm{Cs}$, unlike it has been suggested in earlier studies. We present the first theoretical investigation of chiral geometry and its correlation with the single-particle configurations in $^{130}\mathrm{La}$ to understand the mode of chirality, i.e., static or vibrational.

Comparative analysis of s-wave and p-wave breakups in 37Mg +208Pb reaction

A comparative study of [Formula: see text]-wave and [Formula: see text]-wave breakups in the [Formula: see text] reaction around the Coulomb barrier is presented. The elastic scattering, breakup and reaction cross-sections, corresponding to the three [Formula: see text], [Formula: see text] and [Formula: see text] possible single-particle configurations in the [Formula: see text] ground state, calculated with two different [Formula: see text] ground-state binding energies, namely 0.22 and 0.49[Formula: see text]MeV are analyzed. As in the breakup of other neutron-halo systems such as [Formula: see text], it is found that for all three ground-state configurations, couplings to the breakup channels suppress the Coulomb–nuclear interference peak in the elastic scattering cross-section. It is shown that the breakup through [Formula: see text]-wave ground state is dominated by couplings to continuum [Formula: see text]-waves, whereas the breakup through [Formula: see text]-wave ground state, is largely dominated by couplings to continuum [Formula: see text]-wave. Substantially larger [Formula: see text] ground state total, Coulomb and nuclear breakup cross-sections than their [Formula: see text] and [Formula: see text] ground states counterparts are obtained. This is understood to mainly originate from a larger electric dipole response function of the transition from [Formula: see text] ground state to the continuum, and from the fact that the Coulomb breakup cross-section is directly proportional to this function. In conclusion, the breakup of [Formula: see text] nucleus exhibits a similar breakup behavior as other one-neutron loosely bound systems. The results presented in this paper may provide some guidance for experimentalists to analyze possible future experimental data.

Chirality in [formula omitted]Pm

One of the enticing manifestations of broken symmetries in atomic nuclei is the chiral doublet bands. We investigate such bands in 136Pm and 138Pm, to understand the underlying geometries and their correlations with the single-particle configurations. We identify such correlations leading to vibrational or static nature of chirality. Chirality withstands higher spins in 136Pm, unlike 138Pm. Our present calculations for 138Pm, confirm the newly assigned spin and parity 9+ state as band-head of the yrast band, based on {πh11/2⊗νh11/2} configuration.

Nanostructuring improves the coupling of dielectric waveguides with plasmonic nanoresonators

Certain metallic nanostructures exhibiting localized surface plasmon resonances (LSPR) are capable of sensing extremely low-volume analytes down to attoliters, especially when used in a single particle configuration. Incorporating them into integrated photonics sensing platforms could result in a reduced limit of detection (LOD), and increased dynamic range and multiplexing capabilities. Despite the potential of this platform, several challenges remain, like low coupling efficiencies between integrated waveguides and plasmonic nanoantennae, and the need for off-chip readout. We numerically investigate the optical response of phase shifted Bragg grating (PSBG) and sub-wavelength grating (SWG) waveguides loaded with plasmonic nanoresonators in silicon nitride (Si3N4) integrated photonics platform operating in an aqueous environment. In comparison with a strip waveguide, a 3-4 times improvement in coupling, up to 5 times improvement in local intensity enhancement and 6-7 times improvement in intensity-shift sensitivity are predicted for the structured waveguide configurations. In particular, the PSBG configuration exhibited slightly improved coupling and intensity-shift sensitivity compared to the SWG configuration. On the other hand, the device footprint of the SWG configuration was only a fifth of that of PSBG and also exhibited nearly two times larger local intensity enhancement. A systematic study of the design space and sensitivity analysis is performed to assess the optimal configuration for single-ID single-wavelength refractometric sensing, on-chip excitation and off-chip readout, and SERS sensing.

Spectroscopic investigation of complex nuclear excitations in Ga66

In-beam spectroscopic technique using the fusion evaporation reaction $^{52}\mathrm{Cr}(^{18}\mathrm{O},1p3n)$, at a beam energy of 72.5 MeV, was employed to explore the structural phenomena in $^{66}\mathrm{Ga}$, mainly at intermediate and high spins. The experimental setup involved an array of 14 Compton suppressed Ge clover detectors, placed around the target position to detect emitted $\ensuremath{\gamma}$ rays from excited states. A new level scheme has been proposed, which is enriched with more than 20 new transitions and is extended up to an excitation energy $\ensuremath{\approx}12$ MeV. A few observed intermediate spin states of $^{66}\mathrm{Ga}$ are discussed in the framework of coupling of single-particle configurations with the vibrational core of $^{64}\mathrm{Zn}$. Shell model calculations have also been performed with two different interactions, viz., jj44bpn and jun45pn, for the interpretation of the observed level structure in $^{66}\mathrm{Ga}$.

In-beam γ -ray and electron spectroscopy of Md249,251

The odd-$Z$ $^{251}$Md nucleus was studied using combined $\gamma$-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the $[521]1/2^-$ configuration, another rotational structure has been identified using $\gamma$-$\gamma$ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a $[514]7/2^-$ single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of $\simeq$ 60% was well reproduced by simulating a set of unresolved excited bands. Moreover, a detailed analysis of the intensity profile as a function of the angular momentum provided a method for deriving the orbital gyromagnetic factor, namely $g_K = 0.69^{+0.19}_{-0.16}$ for the ground-state band. The odd-$Z$ $^{249}$Md was studied using $\gamma$-ray in-beam spectroscopy. Evidence for octupole correlations resulting from the mixing of the $\Delta l = \Delta j = 3$ $[521]3/2^-$ and $[633]7/2^+$ Nilsson orbitals were found in both $^{249,251}$Md. A surprising similarity of the $^{251}$Md ground-state band transition energies with those of the excited band of $^{255}$Lr has been discussed in terms of identical bands. Skyrme-Hartree-Fock-Bogoliubov calculations were performed to investigate the origin of the similarities between these bands.

Two-neutron knockout as a probe of the composition of states in Mg22,Al23 , and Si24

Simpson and Tostevin proposed that the width and shape of exclusive parallel momentum distributions of the A-2 residue in direct two-nucleon knockout reactions carry a measurable sensitivity to the nucleon single-particle configurations and their couplings within the wave functions of exotic nuclei. We report here on the first benchmarks and use of this new spectroscopic tool. Exclusive parallel momentum distributions for states in the neutron-deficient nuclei $^{22}$Mg, $^{23}$Al, and $^{24}$Si populated in such direct two-neutron removal reactions were extracted and compared to predictions combining eikonal reaction theory and shell-model calculations. For the well-known $^{22}$Mg and $^{23}$Al nuclei, measurements and calculations were found to agree, supporting the dependence of the parallel momentum distribution width on the angular momentum composition of the shell-model two-neutron amplitudes. In $^{24}$Si, a level at 3439(9) keV, of relevance for the important $^{23}$Al(p,$\gamma$)$^{24}$Si astrophysical reaction rate, was confirmed to be the $2^+_2$ state, while the $4^+_1$ state, expected to be strongly populated in two-neutron knockout, was not observed. This puzzle is resolved by theoretical considerations of the Thomas-Ehrman shift, which also suggest that a previously reported 3471-keV state in $^{24}$Si is in fact the ($0^+_2$) level with one of the largest experimental mirror-energy shifts ever observed.