Transition Strengths Research Articles

Noniterative finite amplitude methods forE1andM1giant resonances

The finite amplitude method (FAM) is a very efficient approach for solving the fully self-consistent random-phase approximation (RPA) equations. We use FAM to rederive the RPA matrices for general Skyrme-like functionals, calculate the electric dipole (E1) and the magnetic dipole (M1) giant resonances, and compare the results with available experimental and evaluated data. For the E1 transitions in heavy nuclei, the calculations reproduce well the resonance energy of the photoabsorption cross sections. In the case of M1 transitions, we show that the residual interaction does not affect the transition strength of double-magic nuclei, which suggests that the spin terms in the Skyrme force currently neglected in the present computation could improve the agreement between FAM and experimental data.

Inner-shell excitation in the YbF molecule and its impact on laser cooling

The YbF molecule is a sensitive system for measuring the electron’s electric dipole moment. The precision of this measurement can be improved by direct laser cooling of the molecules to ultracold temperature. However, low-lying electronic states arising from excitation of a 4f electron may hinder laser cooling. One set of these “4f hole” states lies below the A2Π1/2 excited state used for laser cooling, and radiative decay to these intermediate levels, even with branching ratios as small as 10−5, can be a hindrance. Other 4f hole states lie very close to the A2Π1/2 state, and a perturbation results in states of mixed character that are involved in the laser cooling cycle. This perturbation may enhance the loss of molecules to states outside of the laser cooling cycle. We model the perturbation of the A2Π1/2 state to determine the strength of the coupling between the states, the de-perturbed potential energy curves, and the radiative branching ratios to various vibrational levels of the ground state, X2Σ+. We use electronic structure calculations to characterize the 4f hole states and the strengths of transitions between these states and the A2Π1/2 and X2Σ+ states. We identify a leak out of the cooling cycle with a branching ratio of roughly 5×10−4, dominated by the contribution of the ground state configuration in a 4f hole state. Finally, we assess the impact of these results for laser cooling of YbF and molecules with similar structure.

Spectral Behaviour of the low concentrations of Coumarin 334 with Broadband Cavity Enhanced Absorption Spectroscopy

The current research is a spectroscopic study of Coumarin 334 dissolved in methanol. The range of concentrations of the prepared stock solution was (3.39x10-9 to 2.03x10-8) M. Some optical characteristics of this dye were investigated such as absorbance and transmission spectra, absorption coefficient, refractive and extinction coefficients, oscillation and dispersion energies, and energy band gap. The absorbance spectra were recorded at 452 nm using Broad Band Cavity Enhanced Absorption Spectroscopy (BBCEAS) which depends on increasing the path length of the traveling light from the source to the detector. The minimum absorbance amount was 0.07 with a low concentration of 3.39x10-9 M. As a result, the other optical properties were calculated on the basis of the lowest values of absorbance. The energy band gap, which is important to detect the electronic band structure of the material, was determined; it was found to be equal to ~2.55 eV. The low values of the concentration made less collision between the molecules in the materials and the incident light. This led to a reduction in the background noise and in the percentages of losses. Furthermore, the dispersion and single oscillator energies, which help to calculate the average strength of the inter-band optical transitions and to prepare the quantifiable information about the band structure of the material, were calculated to reduce with the increasing concentrations. The refractive and extinction coefficients were determined because they are considered important factors for the optical materials and found to increase with the increasing concentrations. As a result, the study of the optical behavior of Coumarin 334 highlighted the promising materials for photonics applications at very low concentrations. All these properties are considered the main factors to determine the usefulness of the materials in advanced applications and to develop the performance of the devices which depend on the optical characteristics.

Complete crystal-field calculation of Zeeman hyperfine splittings in europium

Computational crystal-field models have provided consistent models of both electronic and Zeeman-hyperfine structure for several rare earth ions. These techniques have not yet been applied to the Zeeman-hyperfine structure of Eu$^{3+}$ because modeling the structure of the $J=0$ singlet levels in Eu$^{3+}$ requires inclusion of the commonly omitted lattice electric quadrupole and nuclear Zeeman interactions. Here, we include these terms in a computational model to fit the crystal field levels and the Zeeman-hyperfine structure of the $^7F_0$ and $^5D_0$ states in three Eu$^{3+}$ sites: the C$_{4v}$ and C$_{3v}$ sites in CaF$_2$ and the C$_2$ site in EuCl$_3$.6H$_2$O. Close fits are obtained for all three sites which are used to resolve ambiguities in previously published parameters, including quantifying the anomalously large crystal-field-induced state mixing in the C$_{3v}$ site and determining the signs of Zeeman-hyperfine parameters in all three sites. We show that this model allows accurate prediction of properties for Eu$^{3+}$ important for quantum information applications of these ions, such as relative transition strengths. The model could be used to improve crystal field calculations for other non-Kramers singlet states. We also present a spin Hamiltonian formalism without the normal assumption of no $J$ mixing, suitable for other rare earth ion energy levels where this effect is important.

Evolution of low-lying M1 modes in germanium isotopes

Magnetic dipole strength functions are determined for the series of germanium isotopes from $N=Z=32$ to $N$ = 48 on the basis of a large number of transition strengths calculated within the shell model. The evolution of the strength with increasing neutron number in the $1{g}_{9/2}$ orbital is analyzed. A bimodal structure comprising an enhancement toward low transition energy and a resonance in the region of the scissors mode is identified. The low-energy enhancement is strongest near closed shells, in particular at the almost completely filled $1{g}_{9/2}$ orbital, while the scissorslike resonance is most pronounced in the middle of the open shell, which correlates with the magnitude of the also deduced electric quadrupole transition strengths. The results are consistent with previous findings for the shorter series of iron isotopes and prove the occurrence and correlation of the two low-lying magnetic dipole modes as a global structural feature.

Coulomb excitation of the |Tz|=12, A=23 mirror pair

Background: Electric-quadrupole ($E2$) strengths relate to the underlying quadrupole deformation of a nucleus and present a challenge for many nuclear theories. Mirror nuclei in the vicinity of the line of $N=Z$ represent a convenient laboratory for testing deficiencies in such models, making use of the isospin-symmetry of the systems. Purpose: Uncertainties associated with literature $E2$ strengths in \textsuperscript{23}Mg are some of the largest in $T_z=\left|\frac{1}{2}\right|$ nuclei in the $sd$-shell. The purpose of the present work is to improve the precision with which these values are known, to enable better comparison with theoretical models. Methods: Coulomb-excitation measurements of $^{23}$Mg and $^{23}$Na were performed at the TRIUMF-ISAC facility using the TIGRESS spectrometer. They were used to determine the $E2$ matrix elements of mixed $E2$/$M1$ transitions. Results: Reduced $E2$ transition strengths, $B(E2)$, were extracted for \textsuperscript{23}Mg and \textsuperscript{23}Na. Their precision was improved by factors of approximately six for both isotopes, while agreeing within uncertainties with previous measurements. Conclusions: A comparison was made with both shell-model and {\it ab initio} valence-space in-medium similarity renormalization group calculations. Valence-space in-medium similarity-renormalization-group calculations were found to underpredict the absolute $E2$ strength - in agreement with previous studies.

First observation of the π0h11/2⊗ν0h9/2 partner orbital configuration in the odd-odd I138 nucleus

The β-decay scheme of Te138 and the level structure of I138 is reported for the first time. The experiment was performed at the Radioactive Isotope Beam Factory of RIKEN, as one of the EUROBALL-RIKEN Cluster Array campaigns. Secondary radioactive ions, including Te138 and Sb138, were produced by the in-flight fission of a U238 beam with the energy of 345 MeV per nucleon. From the β decay of Te138, the level scheme of I138 was supplemented with new spin and parity assignments, such as the low-lying negative-parity states and a positive-parity 1+ state. This 1+ state can be interpreted as being associated with the π0h11/2⊗ν0h9/2 partner orbital configuration populated by the Gamow-Teller transition between a neutron in the 0h9/2 orbital and a proton in the 0h11/2 orbital. Details of the structure of I138 are discussed in terms of the proton-neutron interactions and Gamow-Teller transition strength within the theoretical context of shell-model calculations.Received 5 December 2021Accepted 16 March 2022DOI:https://doi.org/10.1103/PhysRevC.105.034334©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBeta decayNuclear structure & decaysProperties90 ≤ A ≤ 149TechniquesRadiation detectorsRadioactive beamsShell modelSpectrometers & spectroscopic techniquesNuclear Physics

Nature of seniority symmetry breaking in the semimagic nucleus Ru94

Direct lifetime measurements via γ−γ coincidences using a fast timing detector array consisting of LaBr3(Ce) scintillators has been applied to determine the lifetime of low-lying states in the semimagic (N=50) nucleus Ru94. The experiment was carried out as the first in a series of “FAIR-0” experiments with the DESPEC experimental setup at the Facility for Antiproton and Ion Research (FAIR). Excited states in Ru94 were populated primarily via the β-delayed proton emission of Pd95 nuclei, produced in the projectile fragmentation of an 850 MeV/nucleon Xe124 beam impinging on a 4 g/cm2Be9 target. While the deduced E2 strength for the 2+→0+ transition in the yrast cascade follows the expected behavior for conserved seniority symmetry, the intermediate 4+→2+ transition exhibits a drastic enhancement of transition strength in comparison with pure-seniority model predictions as well as standard shell model predictions in the fpg proton hole space with respect to doubly magic Sn100. The anomalous behavior is ascribed to a subtle interference between the wave function of the lowest seniority ν=2, Iπ=4+ state and that of a close-lying ν=4 state that exhibits partial dynamic symmetry. In addition, the observed strongly prohibitive 6+→4+ transition can be attributed to the same mechanism but with a destructive interference. It is noted that such effects may provide stringent tests of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations.Received 17 October 2021Revised 17 January 2022Accepted 11 March 2022DOI:https://doi.org/10.1103/PhysRevC.105.L031304Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by Bibsam.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasIsomer decaysProton emissionProperties90 ≤ A ≤ 149Nuclear bindingTechniquesGamma ray spectroscopyNuclear structure & decaysRadiation detectorsRadioactive beamsSpectrometers & spectroscopic techniquesNuclear PhysicsAccelerators & Beams

Ultraviolet (UV) irradiated induced changes in optical properties of PVA/Ag nanocomposite films

PVA/Ag nanocomposite with different concentrations of silver nanoparticles (Ag NPs) was successfully synthesized by the solution casting method. The effect of concentration of Ag NPs and ultraviolet (UV) irradiation on optical and structural properties of PVA/Ag nanocomposites were investigated by UV-Vis spectrophotometer and Fourier transform infrared spectroscopy. The presence of an absorption peak at around 410 nm recorded by UV-Vis spectrophotometer shows silver nanoparticles are formed. The absorption spectra for prepared nanocomposites recorded over the wavelength range of 200–700 nm shows the intensity of absorption band increases with an increase in the concentration of Ag NPs and with the increase in time of ultraviolet (UV) irradiation. Decreases in the broadness of transmission band with an increment in enfeeblement transmission intensity by UV exposure make its use suitable as a bandpass filter. Decrease in the value of the optical band gap from 4.91 eV for pure PVA to 4.32 eV for PVA doped 0.04M Ag was observed which continuously reduces further with an increase in the concentration of Ag NPs (3.67 eV for PVA doped 0.08M Ag). Additionally, as the time for UV exposure increases the value of the optical band gap decreases from 4.32 eV without UV exposure to 3.81 eV and 3.43 eV for UV exposure of 120 min and 240 min respectively for PVA doped 0.04M Ag. This reduction in values of the optical band gap corresponds to the formation of charge formation complexes inside the PVA matrix. Various optical parameters such as refractive index, single oscillator energy, lattice dielectric constant, the strength of interband optical transition, average oscillator strength, etc are calculated for nanocomposite with different concentrations of Ag NPs before and after UV exposure for different times. The refractive index values were observed to increase from 1.69 for pure PVA to 1.85 without UV exposure, which further increases to 2.30 for UV exposure of 240 min for PVA doped 0.08M Ag. FTIR spectra show the interaction between PVA and Ag NPs and show changes caused in the structure of nanocomposite as the time of UV exposure increases.

Photodisintegration cross section of deuteron

The peak produced by the M1 and E1 transition strengths for the photodisintegration cross section of deuteron is calculated in the complex scaling method and the origin of the peak of the M1 strength near threshold energy is discussed.

Tensor force effect on pairing correlations for the Gamow–Teller transition in 42Ca, 46Ti, and 18O

Abstract We investigate the tensor force (TF) effect on the Gamow–Teller (GT) transition strength distributions in 42Ca, 46Ti, and 18O, which are known to have strong low-energy GT states, the so-called low-energy super GT (LeSGT) transition, peculiar to nuclei retaining a neutron number N = Z + 2. The TF is explicitly taken into account in the pairing channels of the residual interaction on top of the mean field described by a deformed Woods–Saxon potential. The pairing matrix elements (PMEs) comprising isoscalar and isovector parts, which consistently describe both the ground and the GT excited states, are calculated by a Brückner G-matrix based on the charge-dependent Bonn potential. By switching the TF on and off in the PMEs, we deduce meaningful correlations between the TF and the GT strength distributions. It is found that an attractive TF affects not only the ground state but also plays a crucial role in shifting the main GT peak to the low excitation-energy region leading to the LeSGT.

Electric Dipole Transition of the First Excited State of 9Be

The E1 transition strength of the 1/2+ first excited state of 9Be is calculated using three bodycluster model and complex scaling method where the excited state is correctly treated asunbound. The 1/2+ resonance is obtained using the attractive three-body potential.

Spectral Characteristic of Phosgene in External Electric Field

Phosgene is highly toxic, and it plays a role in the depletion of the ozone layer. The ground state geometric structure and spectral characteristic of phosgene in various external electric fields were calculated via the density-functional theory (DFT) and time-dependent density-functional theory (TDDFT) with the B3LYP/6-31+G(d) basis set. With external electric field, the structure of phosgene changed significantly. With increasing electric field, the bond lengths of 1C-3Cl and 1C-4Cl increased; the total energy and energy gap initially increased and then decreased, whereas the dipole moment initially decreased and then increased. Most of the IR vibrational frequencies were redshifted. The wavelength of the singlet excited state increased, reflecting a red shift, and the oscillator strengths of most transitions belonged to forbidden transitions. These results are of great significance for studying the dissociation of phosgene in external electric field.

Shell-model calculation of Mo100 double- β decay

For the first time, the calculation of the nuclear matrix element of the double-$\beta$ decay of $^{100}$Mo, with and without the emission of two neutrinos, is performed in the framework of the nuclear shell model. This task is accomplished starting from a realistic nucleon-nucleon potential, then the effective shell-model Hamiltonian and decay operators are derived within the many-body perturbation theory. The exotic features which characterize the structure of Mo isotopes -- such as shape coexistence and triaxiality softness -- push the shell-model computational problem beyond its present limits, making it necessary to truncate the model space. This has been done with the goal to preserve as much as possible the role of the rejected degrees of freedom in an effective approach that has been introduced and tested in previous studies. This procedure is grounded on the analysis of the effective single-particle energies of a large-scale shell-model Hamiltonian, that leads to a truncation of the number of the orbitals belonging to the model space. Then, the original Hamiltonian generates a new one by way of a unitary transformation onto the reduced model space, to retain effectively the role of the excluded single-particle orbitals. The predictivity of our calculation of the nuclear matrix element for the neutrinoless double-$\beta$ decay of $^{100}$Mo is supported by the comparison with experiment of the calculated spectra, electromagnetic transition strengths, Gamow-Teller transition strengths and the two-neutrino double-beta nuclear matrix elements.

Bubble wall velocities in local equilibrium

It is commonly expected that a friction force on the bubble wall in a first-order phase transition can only arise from a departure from thermal equilibrium in the plasma. Recently however, it was argued that an effective friction, scaling as γ2 w (with γ w being the Lorentz factor for the bubble wall velocity), persists in local equilibrium. This was derived assuming constant plasma temperature and velocity throughout the wall. On the other hand, it is known that, at the leading order in derivatives, the plasma in local equilibrium only contributes a correction to the zero-temperature potential in the equation of motion of the background scalar field. For a constant plasma temperature, the equation of motion is then completely analogous to the vacuum case, the only change being a modified potential, and thus no friction should appear. We resolve these apparent contradictions in the calculations and their interpretation and show that the recently proposed effective friction in local equilibrium originates from inhomogeneous temperature distributions, such that the γ2 w -scaling of the effective force is violated. Further, we propose a new matching condition for the hydrodynamic quantities in the plasma valid in local equilibrium and tied to local entropy conservation. With this added constraint, bubble velocities in local equilibrium can be determined once the parameters in the equation of state are fixed, where we use the bag equation in order to illustrate this point. We find that there is a critical value of the transition strength αcrit such that bubble walls run away for α>αcrit.

Substituent effects on the UV-visible spectrum and excited electronic states of dithiocarboxylates.

The absorption spectra of a series of dithiocarboxylates were investigated in the ultraviolet-visible region. Two questions that this study aimed to address were as follows: (1) What transitions give rise to the features in the electronic spectra? And (2) what are the long- and short-range substituent effects on the absorption spectra? A series of 11 dithiocarboxylates were prepared as organic soluble salts. Time-dependent density functional theory (TDDFT) was used to calculate excited state energies and oscillator strengths of electronic transitions. TDDFT at the CAM-B3LYP/def2-TZVPD level of theory predicts two low-energy n → π* transitions and two π → π* transitions at higher energy, consistent with the experimental spectra. This state ordering and density is in contrast to the better studied thiocarbonyls for which only two transitions within the singlet manifold appear in the UV-visible region. For derivatives of dithiobenzoate, the energy of the three lowest energy states are insensitive to changes to substituents para to the dithiocarboxylate group. In contrast, the energy of the highest ππ* state varies by 0.78eV. This work shows that the results of TDDFT calculations can be used to predict the electronic absorption spectra of dithiocarboxylates, providing a useful tool for designing dithiocarboxylate light absorbers.

Evolution of shape and collectivity along the Ge isotopic chain: The case of Ge80

The shape and collectivity of $^{80}\mathrm{Ge}$ were investigated via a sub-barrier-energy Coulomb excitation measurement using the JANUS setup at the NSCL ReA3 facility. The $^{80}\mathrm{Ge}$ spectroscopic quadrupole moment ${Q}_{s}({2}_{1}^{+})$ of the ${2}_{1}^{+}$ state was measured for the first time, and the precision of the $^{80}\mathrm{Ge}$ $B(E2;{0}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ transition strength was increased. The experimental ${Q}_{s}({2}_{1}^{+})$ value indicates a large, prolate deformation for $^{80}\mathrm{Ge}$, which is consistent with large-scale shell-model calculations performed for comparison. These results provide important benchmarks for models that try to describe nuclear shape in neutron-rich nuclei near the magic number $N=50$.

Core-shell type-II spherical quantum dot under externally applied electric field

This study presents a simple one-band model within the effective mass approximation to describe the electric field impact on the energy structure and interband electron quantum transitions in type-II CdSe/ZnTe and ZnTe/CdSe spherical quantum dots. The dependencies of the oscillation strength and the light absorption coefficient on the externally applied electric field are calculated by the diagonalization method for spherical quantum dots of different sizes. It is shown that in the absence of an electric field and due to the spherical symmetry of nanosystem, only quantum transitions with Δl=0 (1se−1sh, 1pe−1ph, 1de−1dh, 1se−2sh,...) are allowed. The oscillator strength of quantum transitions between electron and hole excited states is greater than between the ground states. The electric field breaks the spherical symmetry, therefore, the oscillator strength of the 1se−1ph, 1se−1ph, 1se−1dh,... quantum transitions, which are forbidden for spherical symmetric systems, increase when electric field strength grows. Under electric field effects, the oscillator strength of allowed Δl=0 quantum transitions decreases. Finally, we observed that the absorption peaks in the quantum dot spectra under electric field influence are shifted to the low-energy region.

Half-life measurement of the 199-keV isomeric state in Ga76

Background: Isomeric states in atomic nuclei are a sensitive probe of their underlying microscopic structure and can be used to study the evolution of shell structure far from stability. Recent studies have identified and provided detailed spectroscopy of isomers in neutron-rich nuclei with $Z=28\text{\ensuremath{-}}50$. Isomeric states in the odd-odd gallium isotopes have been reported for all gallium isotopes from $A=72$ to $A=80$ with the exception of $^{76}\mathrm{Ga}$.Purpose: The purpose of this experiment was to observe short-lived isomeric states in the vicinity of $^{78}\mathrm{Ni}$.Methods: In-beam fragmentation of a $^{86}\mathrm{Kr}$ primary beam at the National Superconducting Cyclotron Laboratory produced radioactive ions which were delivered to and deposited in a $\mathrm{Ce}{\mathrm{Br}}_{3}$ scintillator coupled to a position-sensitive photomultiplier tube. Beta-delayed $\ensuremath{\gamma}$ rays were measured by ancillary HPGe clover and $\mathrm{La}{\mathrm{Br}}_{3}$ detectors which surrounded the implantation detector.Results: The previously observed ${J}^{\ensuremath{\pi}}={1}^{+}$, 199-keV level in $^{76}\mathrm{Ga}$, populated following the $\ensuremath{\beta}$ decay of $^{76}\mathrm{Zn}$, was identified as isomeric with a half-life of $34{(1)}_{\text{stat.}}{(8)}_{\text{sys.}}\phantom{\rule{0.16em}{0ex}}\mathrm{ns}$. Shell-model calculations suggest this state is formed by the coupling of protons in negative-parity configurations to $1/{2}^{\ensuremath{-}}$ neutron configurations. Transition strengths assuming a ground-state spin of $J=2$ and $J=3$ were determined from the experimental data.

Shape coexistence in 76Se within the neutron–proton interacting boson model

We have investigated the low-lying energy spectrum and electromagnetic transition strengths in even–even 76Se using the proton–neutron interacting boson model (IBM-2). The theoretical calculation for the energy levels and E2 and M1 transition strengths is in good agreement with the experimental data. Specifically, the excitation energy and E2 transition of state, which is intimately associated with shape coexistence, can be accurately reproduced. The analysis on low-lying states and the key structure indicators R 1, R 2, R 3 and R 4 and M1 transitions indicates that there is a coexistence between spherical shape and γ-soft shape in 76Se.