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Y. Lei

Publications and source records attributed to Y. Lei.

At least 19 recordsLinked to original sources
arXiv2026

General Radial-Composition Correlations in Two-Component Many-Body Systems

The linear correlation between RMS radius difference and composition asymmetry in two-component many-body systems is a robust feature observed across nuclear experiments, diverse nuclear structural models, molecular dynamic simulations for bimetallic clusters, and galactic modeling with self-interacting dark matter. We identify the short-range attractive central force as the key ingredient for its emergence, a mechanism underpinned by the coordinate transformation under low-energy harmonic-oscillator approximation, the virial theorem, and Pauli principle/hard core potential, in many-fermion system/classic many-body system.

nucl-th↗
arXiv2025

Robust linear correlations related to neutron skin thickness

We observe various robust linear correlations related to neutron skin thickness ($\Delta R_{\rm np}$) within different interaction ensembles, including newly proposed random Skyrme ensemble. The robust linear correlation between $\Delta R_{\rm np}$, or charge radius difference of mirror nuclei ($\Delta R_{\rm mirr}$), and the isospin asymmetry ($I=\frac{N-Z}{A}$) becomes apparent as the model space is enlarged. Shape coexistence, or shape effect on charge radius, is considered to explain the experimental deviation of ${}^{18}$O/Ne and some odd-$A$ $\Delta R_{\rm mirr}$s from the $\Delta R_{\rm mirr}-I$ linearity. The slopes of the linear $\Delta R_{\rm mirr}-I$ and $\Delta R_{\rm np}-I$ correlations ($C_{\rm np}$ and $C_{\rm mirr}$, respectively) are also robustly and linearly correlated to the slope of the symmetry energy ($L$). These linear correlations are further understood with the similar formulation between between $L$ and the symmetry energy coefficient ($J$). The linear correlations between $C_{\rm np}-L$ and $C_{\rm mirr}-L$ are also adopted to constrain $L$ to $20\sim36$ MeV with 1$\sigma$ confidence. Considering the deviation of ${}^{18}$O/Ne $\Delta R_{mirr}$ due to shape coexistence, the 1$\sigma$ range for $L$ is further narrowed to $28\sim36$ MeV, suggesting a relatively soft equation of state for nuclear matter.

nucl-th↗
arXiv2024

Robust correlation between binding energies and charge radii of mirror nuclei

Using the charge density from the two-parameter Fermi model, a robust and nontrival correlation between binding energis and charge radii of mirror nuclei is newly proposed. This correlation enables simple yet reliable predictions of the nuclear mass and charge radius of proton-rich nuclei. The validity of these predictions is demonstrated by comparing the predicted binding energies and charge radii with experimental data and predictions from other models. All 197 predicted binding energies and 199 charge radii involved in the comparisons are tabulated in the Supplemental Materials of this paper. The noticeable discrepancies are attributed to the large asymmetry in charge densities of mirror nuclei, suggesting that the proposed correlation could be a sensitive probe for local structural anomaly, such as shell closure and proton halo. The difference in mass dependence of charge radii near the proton dripline compared to those along the $\beta$-stability line supports the validity of our prediction method.

nucl-th↗
arXiv2024

The pervasiveness of shape coexistence in nuclear pair condensates

We investigate nuclear shape coexistence for a wide range of even-even nuclides. By varying general pair condensates, which include Slater determinants as a limit but also allow for arbitrary pairing channels, we frequently find multiple coexisting mimina, and often more than two. This is consistent with recent experimental results. In order to measure general pairwise correlations beyond a simple Slater determinant, we introduce a novel entropy-like measure, which is smallest mid-shell and largest near shell closures; this is consistent with a picture of pairing-like behavior dominating near closed shells and deformation mid-shell. After surveying nuclides spanning from the $sd$ shell to nuclides between magic numbers 50 and 82, we focus on the six lightest nuclei with shape coexistence. Angular-momentum projected variational pair condensate (PVPC) calculations identify band structures, including two newly proposed coexisting bands in $^{26}$Si/Mg and $^{24}$Si/Ne. The PVPC results agree well with data, providing robust experimental support for the pervasiveness of coexistence in these light nuclei.

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arXiv2023

Developing a single phase liquid argon detector with SiPM readout

Liquid argon is used as a target material in several current and planned experiments related to dark matter direct searching and neutrino detection. SiPM is becoming the standard for scintillator detectors because of its advantages over traditional PMT. In this paper, we developed a single-phase liquid argon detector using eight 1 $\times$1 inch$^2$ Hamamatsu S14161-6050HS 4$\times$4 SiPM arrays. The directly measured light yield is 25.7 $\pm$ 1.6 photo-electrons per keV, which corresponds to 12.8 $\pm$ 0.8 photo-electrons primarily generated by the argon scintillation. The rest is contributed by the cross-talk and after-pulse of SiPM. In addition, we provide an experimental method to estimate the effect of crosstalk and afterpulse on light yield using dark noise data. Finally, we quantitatively give the relationship between the light yield and the decay time of the slow component of a liquid argon detector.

physics.ins-det↗
arXiv2022

OMR-NPA: Optimized Matrix Representation of Nucleon Pair Approximation

We optimize the matrix representation of the nucleon-pair approximation (NPA) of the nuclear shell model. The NPA is a widely adopted truncation approach of the nuclear shell model and proves to be effective in describing low-lying states of medium-heavy and heavy nuclei. Due to simplified (yet flexible) commutators and absolute elimination of angular momentum coupling, the matrix representation provides a formalism for the $M$-scheme NPA more efficient than others as far as we know. It also enables the practicable organization and storage design for intermediate results, including generated collective pairs, matrix products, and matrix traces, so that further optimization is achieved by reducing repetitive matrix operations, which are the most time-consuming procedures in the matrix-represented $M$-scheme NPA. We also describe optimizations specified for the $M$-scheme NPA, realized by invoking the Wigner-Eckart theorem, time-reversal symmetry, and conjugate operation of spherical tensors. Our optimization makes the combination of matrix representation and NPA more profitable. Such an implementation denoted by optimized matrix representation of NPA (OMR-NPA) is publicly released with open source. Its performance is analyzed and compared against unoptimized NPA codes.

nucl-th↗
arXiv2020

Nucleon-pair approximation with matrix representation

In this paper, we propose an approach of the nucleon-pair approximation (NPA), in which the collective nucleon pairs are represented in terms of antisymmetric matrices, and commutations between nucleon pairs are given by using matrix multiplication that avoids angular-momentum couplings and recouplings. Therefore the present approach significantly simplifies the NPA computation. Furthermore, it is formulated on the same footing with and without isospin.

nucl-th↗
arXiv2020

Variational approach for pair optimization in the nucleon pair approximation

We propose a pair-condensate variational approach (PCV) to determine a set of the most important collective pairs in the description of low-lying states in atomic nuclei. Having available the precise details on these key collective pairs -- their spin, parity, and structure -- can be particularly useful in calculations based on the nucleon-pair approximation (NPA), helping to reduce their uncertainties. In trial calculations for the transitional Ba isotopes, our variational approach describes the evolution of quadrupole-deformation properties similar to Hartree-Fock treatments, while at the same time highlighting the $γ$ softness of $^{132}$Ba. Our approach can conclusively determine which collective pairs are critical for obtaining the lowest possible yrast, quasi-beta, quasi-gamma bands, producing both the level structure of these bands and related B(E2) values in reasonable consistency with experiment. These trial calculations suggest that with our PCV approach the NPA can be meaningfully applied to transitional nuclei with a wide spectrum of shapes. We also show that while neutron negative-parity pairs could in principle have an important impact on backbending in $^{132}$Ba, they are not favored for this nucleus.

nucl-th↗
arXiv2020

Significant Contribution of Projectile Excited States to the Stopping of Slow Helium Ions in Hydrogen Plasma

The energy deposition and the atomic processes, such as the electron-capture, ionization, excitation and radiative-decays for slow heavy ions in plasma remains an unsolved fundamental problem. Here we investigate, both experimentally and theoretically, the stopping of 100 keV=u helium ions in a well-defined hydrogen plasma. Our precise measurements show a much higher energy loss than the predictions of the semi-classical approaches with the commonly used effective charge. By solving the Time Dependent Rate Equation (TDRE) with all the main projectile states and for all relevant atomic processes, our calculations are in remarkable agreement with the experimental data. We also demonstrated that, acting as a bridge for electron-capture and ionization, the projectile excited states and their radiative decays can remarkably influence the equilibrium charge states and consequently lead to a substantial increasing of the stopping of ions in plasma.

physics.plasm-ph↗
arXiv2017

From local correlations to regional systematics

Local correlations of $2^+_1$ excitation energies and B(E2, $2^+_1\rightarrow \text{ g.s.}$) values require linear $N_pN_n$ systematics in a logarithmic scale, as confirmed by an experiment survey. Based on local correlations of $α$-decay energies, neutron separation energies, and proton separation energies, one can decouple them into their proton and neutron contributions separately. These contributions exhibit smooth regional systematics beyond the $N_pN_n$ scheme.

nucl-th↗
arXiv2016

Global correlations between electromagnetic and spectroscopic properties of collective $2^+_1$ and $2^+_2$ states

By using the general triaxial rotor model (TRM) and the phonon-configuration mixing scheme within an anharmonic-vibrator(AHV) framework, a series of global correlations between electromagnetic properties of nuclear $2^+_1$ and $2^+_2$ states are analytically established. The correlations from both models can roughly describe the experimental data involving quadrupole collectivity with few exceptions. Furthermore, there seems to be a robust orthogonal transformation between the AHV and TRM bases for realistic nuclear systems, suggesting that the two models may in fact be describing the collective features of nuclear low-lying states in similar model spaces.

nucl-th↗
arXiv2016

Robust correlations between quadrupole moments of low-lying $2^+$ states within random-interaction ensembles

In the random-interaction ensembles, three proportional correlations between quadrupole moments of the first two $I^π=2^+$ states robustly emerge, including $Q(2^+_1)=\pm Q(2^+_2)$ correlations consistently with realistic nuclear survey, and the $Q(2^+_2)=-\frac{3}{7}Q(2^+_1)$ correlation, which is only observed in the $sd$-boson space. These correlations can be microscopically characterized by the rotational SU(3) symmetry and quadrupole vibrational U(5) limit, respectively, according to the Elliott model and the $sd$-boson mean-field theory. The anharmonic vibration may be another phenomenological interpretation for the $Q(2^+_1)=- Q(2^+_2)$ correlation, whose spectral evidence, however, is insufficient.

nucl-th↗
arXiv2015

Phase change near $N=70$ in the wave function of the $I^π=11/2^-$ isomers along the cadmium-isotope chain

The electromagnetic features of the $11/2^-$ isomers in the $^{111-127}$Cd isotopes are reproduced by numerically optimized shell-model wave-functions. A sudden phase change of the wave functions at $N = 70$ is identified and further confirmed by the evolution of B(E2, $7/2^-_1\rightarrow 11/2^-_1$) values. This phase change gives rise to different linear relations for the $Q$ and $μ$ values with $N<70$ and $N>70$, as needed to reproduce the experimental data. The particle-hole transformation properties for $h_{11/2}$ neutrons in a well-isolated subshell involving degenerate $s_{1/2}$, $d_{3/2}$, $d_{5/2}$ and $h_{11/2}$ orbits is suggested as a possible explanation for this phase change.

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arXiv2014

Robust upper limit on the neutron single-particle energy of the $i_{13/2}$ orbit

The boundary of the neutron $i_{13/2}$ single-particle energy is investigated with exact shell-model calculations, where random two-body interactions are adopted to overcome the bias from effective interactions. Excitation energies of $3^-_1$ state in $^{134}$Te and $^{136}$Xe, as well as those of $13/2^+_1$ states in $^{135}$Te and $^{137}$Xe, are taken as touchstones of our samplings. A robust upper limit of $\varepsilon_{i13/2}<3.1$ MeV emerges in our calculations, given the mixing of $i_{13/2}$ single-neutron configuration and $f_{7/2}\otimes 3^-$ configuration in $13/2^+_1$ states of $N=83$ isotones.

nucl-th↗
arXiv2014

A new variable for SRS plan quality evaluation based on normal tissue sparing: The Effect of Prescription Isodose Levels

Objectives: A new dosimetric variable, dose dropping speed (DDS), was proposed and used to evaluate normal tissue sparing among stereotactic radiosurgery (SRS) plans with different prescription isodose lines. Methods: Forty plans were generated for 8 intracranial SRS cases, prescribing to isodose levels (IDLs) ranging from 50% to 90% in 10% increments. Whilst maintaining similar coverage and conformity, plans at different IDLs were evaluated in terms of normal tissue sparing using the proposed DDS. The DDS was defined as the greater decay coefficient in a double exponential decay fit of the dose drop-off outside the PTV, which models the steep portion of the drop-off. Provided that the prescription dose covers the whole PTV, a greater DDS indicates better normal tissue sparing. Results: Among all plans, the DDS was found the lowest for the prescription at 90% IDL and the highest for the prescription at 60% or 70%. Beam profile slope change in penumbra and its field size dependence were explored and given as the physical basis of the findings. Conclusions: A variable was proposed for SRS plan quality evaluation. Using this measure, prescriptions at 60% and 70% IDLs were found to provide best normal tissue sparing. Advances in knowledge: A new variable was proposed based on which normal tissue sparing was quantitatively evaluated, comparing different prescription IDLs in SRS.

physics.med-ph↗
arXiv2014

Visible light enhanced field effect at LaAlO3/SrTiO3 interface

Electrical field and light-illumination have been two most widely used stimuli in tuning the conductivity of semiconductor devices. Via capacitive effect electrical field modifies the carrier density of the devices, while light-illumination generates extra carriers by exciting trapped electrons into conduction band1. Here, we report on an unexpected light illumination enhanced field effect in a quasi-two-dimensional electron gas (q2DEG) confined at the LaAlO3/SrTiO3 (LAO/STO) interface which has been the focus of emergent phenomenon exploration2-14. We found that light illumination greatly accelerates and amplifies the field effect, driving the field-induced resistance growth which originally lasts for thousands of seconds into an abrupt resistance jump more than two orders of magnitude. Also, the field-induced change in carrier density is much larger than that expected from the capacitive effect, and can even be opposite to the conventional photoelectric effect. This work expands the space for novel effect exploration and multifunctional device design at complex oxide interfaces.

cond-mat.mtrl-sci↗
arXiv2014

Energy deposition by heavy ions: Additivity of kinetic and potential energy contributions in hillock formation on CaF2

The formation of nano-hillocks on CaF2 crystal surfaces by individual ion impact has been studied using medium energy (3 and 5 MeV) highly charged ions (Xe19+ to Xe30+) as well as swift (kinetic energies between 12 and 58 MeV) heavy ions. For very slow highly charged ions the appearance of hillocks is known to be linked to a threshold in potential energy while for swift heavy ions a minimum electronic energy loss is necessary. With our results we bridge the gap between these two extreme cases and demonstrate, that with increasing energy deposition via electronic energy loss the potential energy threshold for hillock production can be substantially lowered. Surprisingly, both mechanisms of energy deposition in the target surface seem to contribute in an additive way, as demonstrated when plotting the results in a phase diagram. We show that the inelastic thermal spike model, originally developed to describe such material modifications for swift heavy ions, can be extended to case where kinetic and potential energies are deposited into the surface.

cond-mat.mtrl-sci↗