E2 Transition Research Articles

Radiative rates for E1, E2, M1, and M2 transitions in F-like ions with 12 [formula omitted] Z [formula omitted] 23

In this paper, energy levels, radiative rates and lifetimes are reported for 11 F-like ions with 12 ≤ Z ≤ 23. Up to 198 levels (depending on the ion) have been considered which include 113 of the 2s22p5, 2s2p6, 2s22p43ℓ, 2s2p53ℓ, and 2p63ℓ configurations. The general-purpose relativistic atomic structure package (grasp) and the flexible atomic code (fac) have been adopted for calculating the energy levels, but the grasp alone for the remaining parameters. Radiative rates (along with oscillator strengths and line strengths) are listed for all E1, E2, M1, and M2 transitions of the ions. Comparisons are made with earlier available theoretical and experimental energies, for all ions, in order to assess the accuracy of the calculations. Comparisons have also been made for the radiative rates and lifetimes, which have been possible for only those among the lowest 60 levels.

Isoscalar giant resonance in 100,116,132Sn isotopes using Skyrme HF-RPA

Fully self-consistent spherical Hartree–Fock HF based random-phase approximation RPA calculations were performed for tin isotopes 100,116,132Sn using five type of Skyrme interaction: QMC2, LNS5, BsK21, NRAPR and MSKA. Isoscalar E0, E1, E2 and E3 transition strength distribution, centroid energy and transition density distribution have been investigated and compared with the available experimental data. Relations between the parameters and properties of the investigated Skyrme force, with the calculated properties of nuclei are analyzed.

Structural investigation of neutron-deficient Pt isotopes: the case of 178Pt

Lifetime measurements with the recoil distance Doppler-shift technique have been performed to determine yrast E2 transition strengths in 178Pt. The experimental data are related to those on neighboring Pt isotopes, especially recent data on 180Pt, and compared to calculations within the interacting boson model and a Hartree-Fock Bogoliubov approach. These models predict prolate deformed ground states in Pt isotopes close to neutron midshell consistent with the experimental findings. Further, evidence was found that the prolate intruder structure observed in neutron-deficient Hg isotopes that is minimum in energy in 182Hg becomes the ground state configuration in 178Pt and neighboring 180Pt with nearly identical transition quadrupole moments. The new data on 178Pt are further discussed in the context of the systematics along the Pt isotopic chain with respect to a possible sharp shape transition towards a weakly deformed or a quasi-vibrational ground state whereas the prolate structure increases in energy in 174,176Pt and becomes an intruder configuration similar to, for example, 180,182Hg.

Confirming band assignments in 167ytterbium with gamma-gamma-electron triple-coincidence spectroscopy

Multipolarity measurements are presented for transitions in the deformed odd-mass nucleus 167 Yb in support of tentative spin assignments and level interpretations based upon the cranked-Nilsson model. Internal-conversion coefficients were measured with the SAGE (Silicon And GErmanium) spectrometer confirming several E2 transition assignments. The array of high-purity germanium detectors enabled the recording of high-multiplicity events from which $\gamma\gamma\gamma$ and $\gamma\gamma e^{-}$ data sets were extracted and the technique of high-fold $\gamma$-ray gating was demonstrated to cleanly isolate transitions of interest.

Enhanced Electric Dipole Strength for the Weakly Bound States in ^{27}Ne.

An enhanced low-energy electric dipole (E1) strength is identified for the weakly bound excited states of the neutron-rich isotope ^{27}Ne. The Doppler-shift lifetime measurements employing a combination of the γ-ray tracking array GRETINA, the plunger device, and the S800 spectrograph determine the lower limit of 0.030 e^{2} fm^{2} or 0.052W.u. for the 1/2^{+}→3/2^{-} E1 transition in ^{27}Ne, representing one of the strongest E1 strengths observed among the bound discrete states in this mass region. This value is at least 30 times larger than that measured for the 3/2^{-} decay to the 3/2_{gs}^{+} ground state. A comparison of the present results to large-scale shell-model calculations points to an important role of core excitations and deformation in the observed E1 enhancement, suggesting a novel example of the electric dipole modes manifested in weakly bound deformed systems.

New result for the [formula omitted]Bγ astrophysical S-factor from 10 keV to 5 MeV and reaction rate from 0.01 to 10 T9

The astrophysical S-factor for the process p7Be→8Bγ of radiative capture by the 8B ground state is described up to 5 MeV, within the modified potential cluster model. The signatures of the S-factor resonances at 0.632, 2.18 and 3.36 MeV due to M1 and E2 transitions from the scattering of resonance P13, F33 and D23 waves to the ground P23 state are illuminated using total cross sections, astrophysical S-factors and reaction rates at temperatures from 0.01 to 10.0 T9. Experimental data on the S-factor are reproduced well in the range 100 keV to 3 MeV. The importance of the input of the 0.632 MeV resonance to the reaction rate is proved. Our calculations (performed in advance) confirm the latest data for the S-factor at 19 keV.

Band mixing in 74, 76, 78Kr

A simple two-state mixing model has been applied to members of the two rotational bands containing the two lowest $ 0^{+}$ states in 74, 76, 78Kr . For each even angular momentum J , two physical states are taken to be linear combinations of basis states $ J_{g}$ and $ J_{e}$ . Mixing amplitudes are varied in order to reproduce E2 transition matrix elements. Unique solutions are found for the $ 0^{+}$ and $ 2^{+}$ mixing in all three cases, and for the E2 matrix elements connecting the basis states. The basis-state band containing basis state $ 0_{g}$ is found to be much more collective than the one containing $ 0_{e}$ in 74, 78Kr , and somewhat more collective in 76Kr . From the fit, the amount of basis state $ J_{e}$ in the lower of the two physical J states decreases very rapidly with increasing J . The $ 2^{+}$ wave functions from the fit are used to compute matrix elements for $ 4\leftrightarrow 2$ transitions, some of which are unknown. A sign discrepancy is noted for the $ 2_{2}\rightarrow 4_{1}$ transition matrix element in 74Kr .

Mechanism of the E2 to E1 transition in Ca2+ pump revealed by crystal structures of gating residue mutants

Ca2+-ATPase of sarcoplasmic reticulum (SERCA1a) pumps two Ca2+ per ATP hydrolyzed from the cytoplasm and two or three protons in the opposite direction. In the E2 state, after transferring Ca2+ into the lumen of sarcoplasmic reticulum, all of the acidic residues that coordinate Ca2+ are thought to be protonated, including the gating residue Glu309. Therefore a Glu309Gln substitution is not expected to significantly perturb the structure. Here we report crystal structures of the Glu309Gln and Glu309Ala mutants of SERCA1a under E2 conditions. The Glu309Gln mutant exhibits, unexpectedly, large structural rearrangements in both the cytoplasmic and transmembrane domains, apparently uncoupling them. However, the structure definitely represents E2 and, together with the help of quantum chemical calculations, allows us to postulate a mechanism for the E2 → E1 transition triggered by deprotonation of Glu309.

Proton Countertransport and Coupled Gating in the Sarcoplasmic Reticulum Calcium Pump

The calcium pump of the sarcoplasmic reticulum (SERCA) is an ATP-driven active transporter of Ca2+ ions that functions via an “alternating-access” cycle mechanism. In each cycle, SERCA transports two Ca2+ ions toward the lumen of the sarcoplasmic reticulum and two to three protons to the cytoplasm. How the latter conformational transition is coupled to cytoplasmic release of protons remains poorly understood. The present computational study shows how the mechanism of proton countertransport is coupled to the alternating access gating process in SERCA. Molecular dynamics simulation trajectories are generated starting from a series of configurations taken along the E2 to E1 transition pathway determined by the string method with swarms-of-trajectories. Simulations of different protonation configurations at the binding sites reveal how deprotonation events affect the opening of the cytoplasmic gate. The results show that there is a strong coupling between the chronological order of deprotonation, the entry of water molecules into the TM region, and the opening of the cytoplasmic gate. Deprotonation of E309 and E771 is sequential with E309 being the first to lose the proton. The deprotonation promotes the opening of the cytoplasmic gate but leads to a productive gating transition only if it occurs after the transmembrane domain has reached an intermediate conformation. Deprotonation of E309 and E771 is unproductive when it occurs too early because it causes the re-opening of the luminal gate.

Atomic structure calculations of superheavy noble element oganesson (Z=118)

We calculate the spectrum and allowed E1 transitions of the superheavy element Og (Z=118). A combination of configuration interaction (CI) and perturbation theory (PT) is used (Dzuba \textit{et at.} Phys. Rev. A, \textbf{95}, 012503 (2017)). The spectrum of lighter analog Rn I is also calculated and compared to experiment with good agreement.

Fabrication of Ge:Ga Hyperdoped Materials and Devices Using CMOS-Compatible Ga and Ge Hydride Chemistries.

We report a versatile chemical vapor deposition (CVD) method to dope Ge films with Ga atoms in situ over a wide concentration range spanning from 3 × 1018 to 2.7 × 1020 cm-3. The method introduces a stable and volatile Ga hydride [D2GaN(CH3)2]2 that reacts readily with Ge4H10 to deliver Ga dopants controllably and systematically at complementary metal-oxide-semiconductor compatible ultralow temperatures of ∼360 °C. Thick and monocrystalline layers (1.3 μm) are produced on Si substrates at growth rates approaching 50 nm/min. The doped crystals are fully epitaxial and devoid of misfit defects and Ga precipitates as evidenced by Rutherford backscattering spectrometry, X-ray diffraction, and cross-sectional transmission electron microscopy. The Ga contents measured by secondary ion mass spectrometry and the active carrier concentrations determined by spectroscopic ellipsometry (as well as Hall effect measurements in several cases) are in close agreement, indicating near full activation. Photoluminescence spectra show a strong emission peak at 0.79 eV corresponding to the direct gap E0 transition, evidence of the indirect transition, and additional structures characteristic of p-type Ge. Electroluminescence and I- V curves measured from p(Ga)-i-n photodiodes are found to be at par with those from boron-based reference devices. These results are promising and demonstrate that a single-source CVD approach allows independent control of Ga doping level and junction depth, producing flat dopant profiles, high activation ratios, uniform distributions, and sharp interfaces. This method potentially represents a viable alternative to state-of-the-art boron-based p-type doping and activation of Ge-like materials.

Bose-Einstein condensation of α clusters and new soft mode in C12 – Fe52 4N nuclei in a field-theoretical superfluid cluster model

Bose-Einstein condensation of alpha clusters in light and medium-heavy nuclei is studied in the frame of the field theoretical superfluid cluster model. The order parameter of the phase transition from the Wigner phase to the Nambu-Goldstone phase is a superfluid amplitude, square of the moduli of which is the superfluid density distribution. The zero mode operators due to the spontaneous symmetry breaking of the global phase in the finite number of alpha clusters are rigorously treated. The theory is systematically applied to N alpha nuclei from12C-52Fe at various condensation rates. In 12C it is found that the energy levels of the gas-like well-developed alpha cluster states above the Hoyle state are reproduced well in agreement with experiment for realistic condensation rates of alpha clusters. The electric E2 and E0 transitions are calculated and found to be sensitive to the condensation rates. The profound raison d'etre of the alpha cluster gas-like states above the Hoyle state, whose structure has been interpreted geometrically in the nuclear models without the order parameter such as the cluster models or ab initio calculations, is revealed. It is found that in addition to the Bogoliubov-de Gennes vibrational mode states collective states of the zero mode operators appear systematically at low excitation energies from the N alpha threshold energy. These collective states, new-type soft modes in nuclei due to the Bose-Einstein condensation of the alpha clusters, emerge systematically in light and medium-heavy mass regions and are also located at high excitation energies from the ground state in contrast to the traditional concept of soft mode in the low excitation energy region.

E0 transition strengths in 110Pd

Internal conversion coefficients have been measured for transitions in 110Pd to allow the determination of electric monopole (E0) transition strengths. Excited states were populated through inelastic alpha scattering and the SPICE+TIGRESS detectors at TRIUMF-ISAC-II were used to detect the emitted gamma rays and internal conversion electrons. The E0 transition strengths are found to be small and are consistent with the expectation for transitions from a K = 2 band to the K = 0 ground-state band in the axial rotor model.

Low-energy dipole strength in even–even 152–164Dy isotopes within the quasiparticle random phase approximation (QRPA) including symmetry restoring interactions

A systematic study of the low-lying magnetic (M1) and electric dipole (E1) transitions from ground- to excited-states in the doubly-even 152–164Dy isotopes has been performed within the framework of the rotational (RI-), translational and Galilean invariant (TGI-) Quasiparticle Random Phase Approximation (QRPA). According to the results of the calculations dipole strength is fragmented over several states in 2–4 MeV interval and as a rule, one-phonon Iπ=1+ states are rather fragmented than the one-phonon states with Iπ=1−. It is found that even though almost all the M1 strengths are dominated by the orbital motion, the weaker contributions from spin motion plays a relatively major role in shaping the M1 spectra due to its constructive interference with orbital motion in these energies. For 160,162,164Dy the calculated total M1 transition strengths, centroid energies of M1 resonance and gamma widths at the energies between 2 and 4 MeV are in fair agreement with relevant experiment data. It has been shown that in addition to the ΔK=0E1 transitions there are also E1 transitions with ΔK=1 in the low-energy E1 spectrum of all the even–even Dy isotopes under investigation.

Quartet structure of N = Z nuclei in a boson formalism: The case of 28Si

The structure of the N=Z nucleus 28Si is studied by resorting to an IBM-type formalism with s and d bosons representing isospin T=0 and angular momentum J=0 and J=2 quartets, respectively. T=0 quartets are four-body correlated structures formed by two protons and two neutrons. The microscopic nature of the quartet bosons, meant as images of the fermionic quartets, is investigated by making use of a mapping procedure and is supported by the close resemblance between the phenomenological and microscopically derived Hamiltonians. The ground state band and two low-lying side bands, a β and a γ band, together with all known E2 transitions and quadrupole moments associated with these states are well reproduced by the model. An analysis of the potential energy surface places 28Si, only known case so far, at the critical point of the U(5)–SU(3)‾ transition of the IBM structural diagram.

Relativistic large scale CI calculations of energies, transition rates and lifetimes in Ca-like ions between Co VIII and Zn XI

Energies, E1, E2 and M1 transition rates and lifetimes are reported for the lowest 134 fine-structure levels of the 3p63d2, 3p63d4s, 3p53d3 and 3p63d4p configurations in all Ca-like ions between Co VIII and Zn XI. The calculations have been performed using the multiconfiguration Dirac–Hartree–Fock (MCDHF) and relativistic configuration interaction (RCI) methods. Important core–valance and core–core electron correlation effects are systematically accounted with large scale configuration interaction expansion. The Breit interaction and leading quantum-electrodynamical (QED) contributions such as the vacuum polarization and self-energy corrections are also included in the RCI calculations. The results are compared with the compiled data from the NIST ASD and other calculations to evaluate the accuracy of the present calculations. Our results have good agreement with previous relativistic many-body perturbation theory (RMBPT) calculations and the data from the NIST ASD, except for Zn XI. Present calculations provide some missing data, especially for Cu X and Zn XI, in the NIST ASD.

Breit and QED Effects in Spectra of the 4s2 1S0−4s4p 3P1,1P1 Transitions in the Zn Sequence

The 4s2–4s4p E1 transitions for Zn-like ions from Z in the range 30–92 are calculated using the multiconfi guration Dirac–Hartree–Fock (MCDHF) method. The results obtained are in good agreement with other theoretical and experimental data and demonstrate the applicability of this method to high-precision atomic structure calculations of both few-electron systems and large atomic systems, such as Zn-like ions, along the entire isoelectronic sequence. We also report herein the calculations of many-electron quantum electrodynamic (QED) and Breit effects for the 3P0, 3P1, 3P2, and 1P1 states for all Zn-like ions in the range 30 ≤ Z ≤ 100.

M1 and E2 transition rates from core-excited states in semi-magic 94Ru

Lifetimes of high-spin states have been measured in the semi-magic $(N=50)$ nucleus 94Ru. Excited states in 94Ru were populated in the 58Ni(40Ca, 4p)94Ru* fusion-evaporation reaction at the Grand Accelerateur National d’Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from $\gamma$ -rays emitted while the residual nuclei were slowing down in a thick 6mg/cm^2 metallic 58Ni target. In total eight excited-state lifetimes in the angular momentum range $I = (13-20)\hbar$ have been measured, five of which were determined for the first time. The corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.

Two-neutron and core-excited states in Pb210 : Tracing E3 collectivity and evidence for a new β -decaying isomer in Tl210

Yrast and near-yrast levels up to an I=17ℏ spin value and a 6-MeV excitation energy have been delineated in the “two-neutron” 210Pb nucleus following deep-inelastic reactions involving 208Pb targets and a number of heavy-ion beams at energies ∼25% above the Coulomb barrier. The level scheme was established on the basis of multifold prompt and delayed coincidence relationships measured with the Gammasphere array. In addition to the previously known states, many new levels were identified. For most of the strongly populated states, spin-parity assignments are proposed on the basis of angular distributions. The reinvestigation of the ν(g9/2)2, 8+ isomeric decay results in the firm identification of the low-energy E2 transitions involved in the 8+→6+→4+ cascade, and in a revised 6+ level half-life of 92(10) ns, nearly a factor of 2 longer than previously measured. Among the newly identified states figure spin I=4–10ℏ levels associated with the νg9/2i11/2 multiplet, as well as yrast states involving νg9/2j15/2, νi11/2j15/2, and ν(j15/2)2 neutron couplings. The highest-spin excitations are understood as 1p−1h core excitations and the yrast population is found to be fragmented to the extent that levels of spin higher than I=17ℏ could not be reached. Four E3 transitions are present in the 210Pb yrast decay; three of these involve the g9/2→j15/2 octupole component, as reflected in the 21(2) and >10 Weisskopf unit enhancements of the B(E3) rates of the first two. The fourth, 16+→13−E3 transition corresponds to the 3− core octupole excitation built on the νi11/2j15/2 state, in analogy to a similar E3 coupling to the νj15/2 level in 209Pb. Shell-model calculations performed for two-neutron states and 1p−1h 208Pb core excitations are in good agreement with the data. Evidence was found for the existence of a hitherto unknown high-spin β-decaying isomer in 210Tl. Shell-model calculations of the 210Tl levels suggest the possibility of a 11+ long-lived, β-decaying state, and the delayed yields observed in various reactions fit rather well with a 210Tl assignment.

Multiconfiguration Dirac–Hartree–Fock energy levels, weighted oscillator strengths, transitions probabilities, lifetimes, hyperfine constants, Landé [formula omitted]-factors and isotope shifts of [formula omitted][formula omitted

Energy levels, weighted oscillator strengths and transition probabilities, lifetimes, hyperfine interaction constants, Landé gJ factors and isotope shifts are calculated for all levels of 1s2 and 1snl (n=2−7) configurations of He-like xenon ion (XeLIII). Multiconfigurational Dirac–Hartree–Fock (MCDHF) method is adopted for calculating these spectroscopic data. Comparisons are made with similar data obtained with FAC (Flexible Atomic Code) to assess the accuracy of the results. Transition probabilities are reported for all E1, E2, M1 and M2 transitions from the ground level. Breit interactions and quantum electrodynamics effects are estimated in extensive Relativistic Configuration Interaction (RCI) calculations. Comparisons were made with the available data in the literature and good agreement was found which confirms the reliability of our results. The accuracy of the present calculations is high enough to facilitate identification of many observed spectral lines. Almost all atomic data of He-like xenon ion presented in this paper are calculated for the first time.