Magic Core Research Articles

Inkjet-printed blue InP/ZnS/ZnS quantum dot light-emitting diodes

Inkjet-printed quantum dot light-emitting diodes (QLEDs) are considered to be ideal candidates for use in full-color displays. However, preparation of eco-friendly blue InP QLEDs using inkjet printing techniques remains rather challenging due to the inferior optical properties of QDs. Here, we present the first efficient method for generating inkjet-printed QLEDs with high color purity using blue InP/ZnS/ZnS QDs as the emitting layer. A two-step heat-up and thick shell strategy was employed for the preparation of blue InP/ZnS/ZnS QDs with a photoluminescence (PL) peak at 465 nm, full width at half-maximum of 38 nm, and PL quantum yield (QY) of ∼ 96 %, which are the records for blue InP QDs. We found that the use of a zinc iodide precursor and anhydrous oxygen reaction environment is critical to determining InP core size, and the size distribution of InP cores can be improved by separating formation of InP magic size clusters and cores via a heat-up step at low temperature. We used two kind of zinc precursors to facilitate shell growth, and the engineered shell thickness suppresses energy transfer, enabling InP/ZnS/ZnS QDs film with high PLQYs and contributing to efficient inkjet printing of QLEDs. These results can facilitate the development of blue InP QLEDs for large-area electroluminescent full-color displays.

Shell-model calculations of the spectroscopic properties of neutron-rich calcium isotopes around 40,48Ca cores

With the aim of predicting the possible existence of new magic numbers, we theoretically studied the recently available experimental data for spectroscopic properties of the neutron rich even-even calcium isotopes around Ca 40,48 doubly magic cores. The calculations were performed with the phenomenological interactions for fppn and HO model spaces using the nuclear structure code Nushell. The two-body matrix elements (TBMEs) of the new effective interaction KB3G48 were derived from the microscopic Kuo-Brown’s G-matrix interaction KB3GPN for Ca 40 core. The calculated energies 𝐸(21 +) of the first excited state, the ratio 𝑅4/2 of the excitation energies, the reduced electric transition probabilities 𝐵(𝐸2; 21 + → 01 +) and the ratio 𝐵4/2 of reduced transition probabilities are compared with the available experimental data. The results of this study are an attempt to demonstrate that 𝑁 = 32 or 𝑁 = 34 are new magic numbers for Ca isotopes.

Precision measurement of the magnetic octupole moment in 45Sc as a test for state-of-the-art atomic- and nuclear-structure theory

We report on measurements of the hyperfine A,B and C-constants of the 3d4s2D5/22 and 3d4s2D3/22 atomic states in 45Sc. High-precision atomic calculations of the hyperfine fields of these states and second-order corrections are performed, and are used to extract C5/2=−0.06(6)kHz and C3/2=+0.04(3)kHz from the data. These results are one order of magnitude more precise than the available literature. From the combined analysis of both atomic states, we infer the nuclear magnetic octupole moment Ω=−0.07(53)μNb, including experimental and atomic structure-related uncertainties. With a single valence proton outside of a magic calcium core, scandium is ideally suited to test a variety of nuclear models, and to investigate in-depth the many intriguing nuclear structure phenomena observed within the neighbouring isotopes of calcium. We perform nuclear shell-model calculations of Ω, and furthermore explore the use of Density Functional Theory for evaluating Ω. From this, mutually consistent theoretical values of Ω are obtained, which are in agreement with the experimental value. This confirms atomic structure calculations possess the accuracy and precision required for magnetic octupole moment measurements, and shows that modern nuclear theory is capable of providing meaningful insight into this largely unexplored observable.

Correlations of α -decay properties and isospin-asymmetry

The isospin-asymmetry nuclear chains with $N\ensuremath{-}Z$ from 2 to 60 are investigated to find the correlations of $\ensuremath{\alpha}$-decay properties and isospin asymmetry. Both the proton- and neutron-skin thicknesses of $\ensuremath{\alpha}$ emitters belonging to different $N\ensuremath{-}Z$ chains are tightly aligned along straight lines, the slope of which depends on the shell closure. For even-even $\ensuremath{\alpha}$ emitters, the neutron-skin thickness ${\mathrm{\ensuremath{\Delta}}}_{n}$ multiplied by $N\ensuremath{-}Z$ is a parabolic function of the isospin-asymmetry parameter $I=(N\ensuremath{-}Z)/A$. For the nuclei of incomplete neutron shells, the $\ensuremath{\alpha}$-decay half-life ${T}_{\ensuremath{\alpha}}$ exponentially increases with ${\mathrm{\ensuremath{\Delta}}}_{n}$ in the isospin chain. In the nuclei with valence neutrons and/or protons outside the magic core, ${T}_{\ensuremath{\alpha}}$ exponentially decreases with increasing ${\mathrm{\ensuremath{\Delta}}}_{n}$. The values of ${T}_{\ensuremath{\alpha}}$ and ${Q}_{\ensuremath{\alpha}}$ are almost exponential functions of isospin asymmetry.

Erratum to: Proton density polarization of the doubly magic 40Ca core in 48Ca and EoS parameters

Erratum to: Proton density polarization of the doubly magic 40Ca core in 48Ca and EoS parameters

N = Z even–even proton-rich nuclei and nuclear structure

Nuclear systems near nucleon drip lines have great importance in studying nucleon–nucleon force properties. However, such unstable systems have few experimental data. Due to technical development in recent years, new experimental data assembly provides huge information to analyze possible observation of new phenomena. In the aim of exploring proton-rich nuclei near closed shells, we have studied the even–even Z = N nuclei in $$28<Z<50$$ , $$50<N<82$$ mass region. This study is based on the investigation of the core polarization and the monopole effect originated from the interactions between the magic core and the valence nucleons. In this context, this work includes the calculation of the energy spectra of Zr, Mo, Ru, Pd and Cd nuclei. These calculations were performed in the framework of the nuclear shell model using NuShellX@MSU code. Using recent single-particle energies, the three-body effect consideration introduces some modifications on the effective interaction. By means of the modified interaction, some nuclear properties of the studied nuclei have been evaluated. The results show a reasonable agreement with the available experimental data. The monopole effect is an important component of nucleon–nucleon interaction, in which its consideration gives a reasonably agreement with available data.

Yrast band in the heavy N = Z nucleus ^{88}Ru: alpha -cluster approach

The yrast band in the heavy N = Z nucleus ^{88}Ru is studied in the framework of the alpha -cluster model in combination with double-folding potentials. It is found that the excitation energies of the yrast band in ^{88}Ru can be nicely described within the alpha -cluster approach using a smooth and mildly L-dependent adjustment of the potential strength. This result is similar to well-established alpha -cluster states in nuclei with a (magic core otimes alpha ) structure. Contrary, the yrast bands in neighboring N ne Z nuclei deviate from such a typical alpha -cluster behavior. Finally, the alpha -cluster model predicts reduced transition strengths of about 10 Weisskopf units for intraband transitions between low-lying states in the yrast band of ^{88}Ru.

Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure

Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure

Particle-phonon coupling: Understanding the variety of excitations in the low-lying spectra of odd nuclei

The couplings between particles and vibrations in atomic nuclei play a key role in the understanding of various nuclear properties, as it has been highlighted along several decades. In this contribution, after a short survey of the early discoveries of particle-phonon multiplets around the 208Pb region, we review recent experiments and theoretical attempts to understand low-energy spectra of odd-nuclei close to magic and semi-magic cores, where particle-phonon coupling phenomena play a significant role. The focus will be on nuclei around 48Ca , 132Sn , 208Pb and neutron-rich Ni isotopes. Special emphasis will be given to experimental techniques based on high-resolution $ \gamma$-spectroscopy and to recent theoretical developments aimed at disentangling particle-phonon coupled states and other more hybrid configurations, using the Hybrid Configuration Mixing model that has been recently proposed by the Milano group.

Observation of cluster structure of fission fragments

The manifestation of a new original effect appearing at crossing of the metal foils by fission fragments is reported. The effect takes place predominantly at front impacts. The obtained results suggest that a fragment from conventional binary fission is borne in shape-isomer state which looks like a di-nuclear system with magic core.

Excitations of the magic N=50 neutron-core revealed in Ga81

The high-spin states of the neutron-rich Ga81, with three valence protons outside a Ni78 core, were measured. The measurement involved prompt γ-ray spectroscopy of fission fragments isotopically identified using the combination of the variable mode spectrometer (VAMOS++) and the advanced gamma tracking array (AGATA). The new γ-ray transitions, observed in coincidence with Ga81 ions, and the corresponding level scheme do not confirm the high-spin levels reported earlier. The newly observed high-spin states in Ga81 are interpreted using the results of state-of-the-art large-scale shell model (LSSM) calculations. The lower excitation energy levels are understood as resulting from the recoupling of three valence protons to the closed doubly magic core, while the highest excitation energy levels correspond to excitations of the magic N=50 neutron core. These results support the doubly magic character of Ni78 and the persistence of the N=50 shell closure but also highlight the presence of strong proton-neutron correlations associated with the promotion of neutrons across the magic N=50 shell gap, only few nucleons away from Ni78.Received 11 January 2019Revised 30 April 2019DOI:https://doi.org/10.1103/PhysRevC.100.011301©2019 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasEnergy levels & level densitiesNuclear structure & decaysRare & new isotopesProperties59 ≤ A ≤ 89TechniquesGamma ray spectroscopyShell modelSpectrometers & spectroscopic techniquesNuclear Physics

R-process 130Cd Waiting Point

Most of the elements heavier than Fe in the universe were produced by the so-called r-process. Its mechanism is based on a rapid neutron capture by the nuclei, so that the neutron capture rates are much faster than those of β -decay. When r-process reaches nuclei with magic neutron numbers, the neutron separation or binding energies increase and the process slows down, it has to wait for several β decays to produce heavier nuclei. These magic nuclei are the waiting points. Information about r-process are steel missing and it requires knowledge of the nuclear structure of the neutron rich nuclei. However, the nuclear properties of these nuclei are not sufficiently well understood due to the experimental difficulties in their production. The A=130 isobars with N=82 present one of the most interesting waiting points, because of their positions far from β stability and near the doubly magic 132Sn core, for which theoretical and experimental studies give important information about beta decay half-lives. In this context, we focus on the study of even-even 130 Cd waiting point nuclear properties. We have performed some spectroscopic calculations for energetic spectrum, β -decay half-life evolution in terms of temperature, using recent experimental data, by means of Oxbash nuclear structure code. The getting spectrum is in a reasonably agreement with the available experimental data. However, the calculated β-decay half-life for the studied waiting point is short in comparison with the experimental one.

Microscopic multiphonon approach to nuclei with a valence hole in the oxygen region

An equation of motion phonon method, developed for even nuclei and recently extended to odd systems with a valence particle, is formulated in the hole-phonon coupling scheme and applied to $A=15$ and $A=21$ isobars with a valence hole. The method derives a set of equations which yield an orthonormal basis of states composed of a hole coupled to an orthonormal basis of correlated $n$-phonon states ($n=0,1,2,\ensuremath{\cdots}$), built of constituent Tamm-Dancoff phonons, describing the excitations of a doubly magic core. The basis is then adopted to solve the full eigenvalue problem. The method is formally exact but lends itself naturally to simplifying approximations. Self-consistent calculations using a chiral Hamiltonian in a space encompassing up to two-phonon and three-phonon basis states in $A=21$ and $A=15$ nuclei, respectively, yield full spectra, moments, electromagnetic and $\ensuremath{\beta}$-decay transition strengths, and electric dipole cross sections. The analysis of the hole-phonon composition of the eigenfunctions contributes to clarify the mechanism of excitation of levels and resonances and to understand the reasons of the deviations of the theory from the experiments. Prescriptions for reducing these discrepancies are suggested.

$\alpha$α clustering slightly above 100Sn in the light of the new experimental data on the superallowed $\alpha$α decay

The recently observed $\alpha$-decay chain ${}^{108}\text{Xe}\to{}^{104}\text{Te}\to{}^{100}\text{Sn}$ [K.~Auranen \emph{et al.}, Phys.\ Rev.\ Lett.\ {\bf121}, 182501 (2018)] could provide valuable information on the $\alpha$ clustering in even-even nuclei slightly above the major shells $Z=50$ and $N=50$. In this work, this $\alpha$-decay chain is studied theoretically within the framework of the density-dependent cluster model plus the two-potential approach. We calculate the $\alpha$-decay half-lives of ${}^{104}$Te and ${}^{108}$Xe and study in detail their dependence on the $Q$ value and the density-profile parameters of the core nucleus. Various physical properties of ${}^{104}$Te, the heaviest nucleus with a doubly magic self-conjugate core $+$ $\alpha$, are calculated, with two different assumptions on the renormalization factor of the double-folding potential, which could be a useful reference for future experimental studies.

Octupole phonon model based on the shell model for octupole vibrational states

A model is proposed for a description of the octupole vibrational states based on the nuclear shell model. In this model, a one-octupole-phonon representing the collective octupole vibration across the magic core is introduced onto the shell-model states that are microscopically calculated within the valence nucleon space. With this model, a unified description is now possible for the pure shell-model states made by valence nucleons, and the octupole-phonon states excited on the shell-model states. The model is applied to various nuclei around the $^{208}\mathrm{Pb}$ nucleus. Energy levels and electric octupole transition probabilities are well reproduced for both the pure shell-model states and the octupole vibrational states.

Investigation of nonlinear isoscalar–isovector coupling in a relativistic mean-field model by elastic magnetic electron scattering

In this paper, we study the sensitivity of single valence neutron properties and elastic magnetic form factors to three different relativistic mean-field (RMF) parameter sets: NL3, FSUGold, and IU-FSU. To perform our calculation, seven odd-A nuclei having single valence neutron on top of a magic neutron core: Be7, O17, Ca41, Ni57, Zr91, Ba139, and Pb209 are considered as model nuclei. The wave-function of the outer most neutron orbit, matter density, valence neutron density, and magnetic form factors are numerically calculated. It is shown that there are significant differences between the magnetic form factors in the mediate- and high-momentum transfer regions when calculate with different parameter sets. Such separation is more evident with larger nuclear mass and isospin asymmetry. By fitting to the experimental data, the spectroscopic factors for O17 and Ca41 are obtained. From the fitting, we infer that including the isoscalar–isovector meson self-coupling can give a better performance of the RMF calculation.

Shell-model study of Pb, Bi, Po, At, Rn, and Fr isotopes with masses from 210 to 217

Large-scale shell-model calculations are performed for even-even, odd-mass, and doubly odd nuclei of Pb, Bi, Po, At, Rn, and Fr isotopes in the neutron rich region ($Ng126$) assuming $^{208}\mathrm{Pb}$ as a doubly magic core. Seven orbitals above the magic number 126, the $1{g}_{9/2}$, $0{i}_{11/2}$, $0{j}_{15/2}$, $2{d}_{5/2}$, $3{s}_{1/2}$, $1{g}_{7/2}$, and $2{d}_{3/2}$ orbitals, are considered for neutrons and all the six orbitals between the magic numbers 82 and 126, the $0{h}_{9/2}$, $1{f}_{7/2}$, $0{i}_{13/2}$, $2{p}_{3/2}$, $1{f}_{5/2}$, and $2{p}_{1/2}$ orbitals, are considered for protons. For a phenomenological effective two-body interaction, one set of the monopole-pairing, quadrupole-quadrupole, and multipole-pairing interactions is adopted for all the nuclei considered. The calculated energies and electromagnetic properties are compared with the experimental data. Many isomeric states are analyzed in terms of the shell-model configurations. The spins and parities of some experimentally ambiguous states are suggested.

A New Calculation of Rotational Bands in Alpha-Cluster Nuclei

One of the cluster behaviors observed in light nuclei such as 20Ne and 44Ti is the presence of an alpha particle rotating around a double magic number core. In this work, a theoretical method is used for investigation of rotational spectra of two-particle cluster states. To this end, Deng-Fan potential in addition to Hellman potential is used as the core and cluster potential. Next, given the Wildermuth condition, and proper quantum numbers describing the relative motion of the alpha particle and core, the rotational levels of 20Ne and 44Ti isotopes are calculated. Our studies show that the results are in good agreement with the available data.

Odd nuclei spectroscopy within a self-consistent multiphonon approach

The extension to odd nuclei of the equation of motion phonon method (EMPM) is briefly outlined. It derives and solves iteratively a set of equations of motion which yield an orthonormal basis of states composed of an odd particle coupled to orthonormal multiphonon states, also generated within the EMPM, describing the excitations of a doubly magic core. The basis so obtained is used to solve the eigenvalue problem in the full particle-phonon space. We have applied the method to the odd neighbors of 16O using an optimized chiral potential in a space spanned by particle-core basis states which include up to three-phonons. The calculations have shown that the multiphonon states enhance enormously the density of levels and compress the whole spectrum, consistently with the data. They also contribute substantially to improve the agreement with the experimental moments and transitions strengths.

The γ-ray spectroscopy studies of low-spin structures in 210Bi and 206Tl using cold neutron capture reactions

The γ-coincidence studies of low-spin structures of 210Bi and 206Tl are presented. The 210Bi nucleus, populated in thermal neutron capture reaction, was investigated using EXILL HPGe array at Institut Laue-Langevin in Grenoble. The experimental results were compared to the shell-model calculations allowing to draw the conclusions on the nature of the low-spin excitations populated below the neutron binding energy in 210Bi (4.6 MeV). It has been found that some levels cannot be described by the valence proton and neutron couplings, but may arise from couplings of valence particles to the 3- octupole phonon of the doubly magic 208Pb core. Moreover, preliminary results of a low-spin structure measurements of 206Tl by the γ-coincidence technique, making use of the 205Tl(n,γ)206Tl reaction at the FIPPS prompt γ-ray spectroscopy facility of ILL are shown. The population of a large number of excited states of 206Tl above the ground state up to the neutron binding energy (at 6.5 MeV), within a few units of spin is expected. The analysis involving double and triple γ-coincidences and γγ-angular correlations will allow to significantly extend the experimental information on the energy and spin-parity of the levels in 206Tl. This will help shedding light on the proton-hole and neutron-hole couplings near the doubly magic core 208Pb.