The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Elena Litvinova - One of the best experts on this subject based on the ideXlab platform.
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electric Dipole response of neutron rich calcium isotopes in relativistic quasiparticle time blocking approximation
Physical Review C, 2016Co-Authors: Elena Litvinova, I A EgorovaAbstract:New results for electric Dipole Strength in the chain of even-even calcium isotopes with the mass numbers $A=40--54$ are presented. Starting from the covariant Lagrangian of quantum hadrodynamics, spectra of collective vibrations (phonons) and phonon-nucleon coupling vertices for $J\ensuremath{\le}6$ and natural parity were computed in a self-consistent relativistic quasiparticle random-phase approximation (RQRPA). These vibrations coupled to Bogoliubov two-quasiparticle configurations $(2\mathrm{q}\ensuremath{\bigotimes}\mathrm{phonon})$ formed the model space for the calculations of the Dipole response function in the relativistic quasiparticle time blocking approximation. The calculations in the latter approach were performed for the giant Dipole resonance (GDR) and compared to those obtained with the RQRPA and to available data. The evolution of the Dipole Strength with the neutron number is investigated for both high-frequency GDRs and low-lying Strengths. The development of a pygmy resonant structure on the low-energy shoulder of the GDR is traced and analyzed in terms of transition densities. A dependence of the pygmy Dipole Strength on the isospin asymmetry parameter is extracted.
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low energy Dipole Strength in 112 120 sn
Physical Review C, 2014Co-Authors: Elena Litvinova, J Enders, P Von Neumanncosel, B Ozeltashenov, H Lenske, A M Krumbholz, I Poltoratska, A RichterAbstract:The $^{112,120}\mathrm{Sn}(\ensuremath{\gamma},{\ensuremath{\gamma}}^{\ensuremath{'}})$ reactions below the neutron separation energies have been studied at the superconducting Darmstadt electron linear accelerator S-DALINAC for different endpoint energies of the incident bremsstrahlung spectrum. Dipole Strength distributions are extracted for $^{112}\mathrm{Sn}$ up to 9.5 MeV and for $^{120}\mathrm{Sn}$ up to 9.1 MeV. A concentration of Dipole excitations is observed between 5 and 8 MeV in both nuclei. Missing Strength due to unobserved decays to excited states is estimated in a statistical model. A fluctuation analysis is applied to the photon scattering spectra to extract the amount of the unresolved Strength hidden in the background due to fragmentation. The Strength distributions are discussed within different model approaches such as the quasiparticle-phonon model and the relativistic time blocking approximation, allowing for an inclusion of complex configurations beyond the initial particle-hole states. While a satisfactory description of the fragmentation can be achieved for sufficiently large model spaces, the predicted centroids and total electric Dipole Strengths for stable tin isotopes strongly depend on the assumptions about the underlying mean field.
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low energy limit of the radiative Dipole Strength in nuclei
Physical Review C, 2013Co-Authors: Elena Litvinova, Nikolay BelovAbstract:We explain the low-energy anomaly reported in several experimental studies of the radiative Dipole Strength functions in medium-mass nuclei. These Strength functions at very low $\ensuremath{\gamma}$ energies correspond to the $\ensuremath{\gamma}$ transitions between very close nuclear excited states in the quasicontinuum and attract an increasing interest because of their substantial astrophysical impact. We show that the low-energy enhancement of the Strength functions in highly excited compound nuclei is explained by nucleonic transitions from the thermally unblocked single-quasiparticle states to the single-(quasi)particle continuum. The case of radiative Dipole Strength functions at the nuclear excitation energies typical for the thermal neutron capture is illustrated for ${}^{94,96,98}$Mo and ${}^{116,122}$Sn in comparison to available data.
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fragmentation of spin Dipole Strength in 90zr and 208pb
Physics Letters B, 2012Co-Authors: Tomislav Marketin, Elena Litvinova, Dario Vretenar, P RingAbstract:An extension of time-dependent covariant density functional theory that includes particle–vibration coupling is applied to the charge-exchange channel. Spin-Dipole excitation spectra are calculated an compared to available data for 90Zr and 208Pb. A significant fragmentation is found for all three angular-momentum components of the spin-Dipole Strength as a result of particle–vibration coupling, as well as a shift of a portion of the Strength to higher energy. A high-energy tail is formed in the Strength distribution that linearly decreases with energy. Using a model-independent sum rule, the corresponding neutron skin thickness is estimated and shown to be consistent with values obtained at the mean-field level.
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low lying Dipole response in the relativistic quasiparticle time blocking approximation and its influence on neutron capture cross sections
Nuclear Physics, 2009Co-Authors: Elena Litvinova, P Ring, H P Loens, K Langanke, G Martinezpinedo, T Rauscher, F K Thielemann, V TselyaevAbstract:Abstract We have computed Dipole Strength distributions for nickel and tin isotopes within the Relativistic Quasiparticle Time Blocking Approximation (RQTBA). These calculations provide a good description of data, including the neutron-rich tin isotopes 130,132Sn. The resulting Dipole Strengths have been implemented in Hauser–Feshbach calculations of astrophysical neutron capture rates relevant for r-process nucleosynthesis studies. The RQTBA calculations show the presence of enhanced Dipole Strength at energies around the neutron threshold for neutron rich nuclei. The computed neutron capture rates are sensitive to the fine structure of the low lying Dipole Strength, which emphasizes the importance of a reliable knowledge of this excitation mode.
R Schwengner - One of the best experts on this subject based on the ideXlab platform.
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electric and magnetic Dipole Strength in 66zn
Physical Review C, 2020Co-Authors: R Schwengner, R Massarczyk, N Benouaret, M Scheck, W Tornow, Giorgio Battaglia, T Beck, D Bemmerer, R BeyerAbstract:The Dipole Strength of the $N=28$ closed-shell nuclide $^{54}\mathrm{Fe}$ was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of kinetic energies of 7.5 and 13.9 MeV at the $\ensuremath{\gamma}\mathrm{ELBE}$ facility as well as using quasimonoenergetic and linearly polarized photon beams of 26 different energies within the range from 5.5 to 11.4 MeV at the $\mathrm{HI}\ensuremath{\gamma}\mathrm{S}$ facility. About 100 $J=1$ states were newly identified, out of them 19 with ${1}^{+}$ and 30 with ${1}^{\ensuremath{-}}$ assignments. The quasicontinuum of unresolved transitions was included in the analysis of the spectra and the intensities of branching transitions were estimated on the basis of simulations of statistical $\ensuremath{\gamma}$-ray cascades. As a result, the photoabsorption cross section up to the neutron-separation energy was determined and compared with predictions of the statistical reaction model. The experimental $M1$ Strengths from resolved ${1}^{+}$ states are compared with results of large-scale shell-model calculations.
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exploring enhanced low energy magnetic Dipole Strength in photon scattering
Physical Review C, 2019Co-Authors: R Schwengner, G RusevAbstract:Strengths of $M1$ transitions depopulating high-lying ${1}^{+}$ states and of subsequent transitions in cascades populating the first excited state were determined on the basis of large-scale shell-model calculations for the nuclide $^{54}\mathrm{Fe}$. The results reveal that the spectra of primary $M1$ transitions from ${1}^{+}$ states as well as the subsequent cascades of $M1$ transitions show an enhancement of Strength toward low energy, which is similar to that found for a huge number of transitions between states of a wide spin range as observed in light-ion induced reactions. This allows, in principle, the study of low-energy $M1$ Strength using photon scattering. Based on these results, intensities of $M1$ transitions under experimental conditions are estimated.
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novel data and a new parametrization of the electric Dipole Strength in nuclei with 88 a 116
arXiv: Nuclear Experiment, 2019Co-Authors: E Grosse, G Rusev, R Schwengner, A R Junghans, K Kosev, Klaus D Schilling, A WagnerAbstract:A hitherto unexplored method for the experimental determination of the photon Strength function up to the neutron separation energy was developed at the Radiation Source ELBE in Dresden. It was applied to various heavy nuclei, preferentially to nuclides with increasing distance to the N=50 neutron shell, and it covers the high level density excitation energy range above 4 MeV. The observed quasi-continuous spectra of scattered photons can be -- after a proper correction for multi-step processes -- directly combined to nuclear photo effect data from literature. A remarkably good match of the photon Strengths as measured below and above the neutron emission threshold is observed. The wide energy coverage of the combined data forms an excellent basis to derive a parameterization for the Dipole Strength function fully covering the range across the nucleon separation energies. In addition to the parameters defining the deformation of the nuclear ground states only one additional constant is needed to describe the Dipole Strength in the nuclei with 88
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Dipole Strength distribution in pb 206 for the evaluation of the neutron capture cross section of pb 205
Physical Review C, 2018Co-Authors: T Shizuma, R Massarczyk, R Schwengner, A R Junghans, R Beyer, D Bemmerer, Nobuyuki Iwamoto, A Makinaga, M Dietz, T KoglerAbstract:The Dipole Strength distribution of $^{206}\mathrm{Pb}$ was investigated via a nuclear resonance fluorescence experiment using bremsstrahlung produced with an electron beam at a kinetic energy of 10.5 MeV at the linear accelerator ELBE. We identified 88 states resonantly excited at energies from 3.7 to 8.2 MeV. The analysis of the measured $\ensuremath{\gamma}$-ray spectra includes the quasicontinuum of levels at high energy. Monte Carlo simulation of $\ensuremath{\gamma}$-ray cascades were performed to obtain the intensities of inelastic transitions and branching ratios of the ground-state transitions. The extracted photoabsorption cross section shows enhanced Dipole Strength at the excitation energies around 5.5 and 7 MeV, which may related to a pygmy Dipole resonance. The present $(\ensuremath{\gamma},\ensuremath{\gamma}\ensuremath{'})$ data combined with $(\ensuremath{\gamma},n)$ data from the literature were used for confining input parameters of the statistical calculation code CCONE to derive the neutron-capture cross section of the unstable $^{205}\mathrm{Pb}$ nucleus.
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Dipole Strength in 80se for s process and nuclear transmutation of 79se
Physical Review C, 2016Co-Authors: A Makinaga, R Massarczyk, R Schwengner, D Bemmerer, M Beard, H Otsu, T Alabdullah, M Anders, R Hannaske, R JohnAbstract:The Dipole Strength distribution of $^{80}\mathrm{Se}$ was studied in a photon-scattering experiment by using bremsstrahlung produced with an electron beam of energy 11.5 MeV at the linear accelerator ELBE. We identified $180\phantom{\rule{0.28em}{0ex}}\ensuremath{\gamma}$ transitions up to an energy of 9.6 MeV, and analyzed the Strength in the quasicontinuum of the spectrum. Simulations of statistical $\ensuremath{\gamma}$-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section below the neutron-separation energy derived in this way was combined with the photoabsorption cross section obtained from an earlier $(\ensuremath{\gamma},n)$ experiment and used as an input for the calculation of $^{79}\mathrm{Se}(n,\ensuremath{\gamma})$ reaction rates on the basis of the statistical reaction model.
Minhaeng Cho - One of the best experts on this subject based on the ideXlab platform.
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simultaneous enhancement of transition Dipole Strength and vibrational lifetime of an alkyne ir probe via π d backbonding and vibrational decoupling
Physical Chemistry Chemical Physics, 2019Co-Authors: Dorota Kossowska, Kyungwon Kwak, Giseong Lee, Hogyu Han, Minhaeng ChoAbstract:Alkyne infrared (IR) probes 1–6 with Si and S (or Se) atoms incorporated into the CC bond were synthesized, and the vibrational properties of their CC stretch mode were studied using Fourier transform infrared (FTIR) and femtosecond IR pump–probe (IR PP) spectroscopies in combination with quantum chemical calculations. From FTIR studies, the transition Dipole Strengths (in units of 10−2 D2) of 1–3 having the Si atom were measured to be 1.85, 3.32, and 2.52, whereas those of 4–6 having no Si atom were measured to be 0.13, 0.20, and 0.17, respectively, in CHCl3. Thus, the increase in the transition Dipole Strength of the CC stretch mode upon incorporation of the Si atom into the CC bond is by a factor of about 14 or higher. The large increase in the transition Dipole Strength of the CC stretch mode upon such Si incorporation is attributed to π-d backbonding between the CC group's π and Si atom's d orbitals. From IR PP experiments, the vibrational lifetimes of the CC stretch mode in 1–3 having none, S, and Se atoms were determined to be 5.7 ± 0.7, 13.0 ± 1.1, and 94.2 ± 5.8 ps, respectively, in CHCl3. Thus, the increase in the vibrational lifetime of the CC stretch mode upon incorporation of the S (or Se) atom between the phenyl ring and the CC bond is by a factor of about 2 (or 16) or higher. The large increase in the vibrational lifetime of the CC stretch mode upon such S (or Se) incorporation is attributed to its heavy atom effect impeding vibrational couplings between the CC stretch and phenyl ring vibrations. From two-dimensional infrared (2DIR) experiments, the large transition Dipole Strength and long vibrational lifetime of 3 containing the Si and S (or Se) atoms were shown to enable the measurement of its 2DIR spectra up to 500 ps. The strongly absorbing alkynes with long vibrational lifetimes will be a promising probe of molecular dynamics in nonlinear vibrational spectroscopy and imaging on an extended time scale.
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rational design of an acetylenic infrared probe with enhanced Dipole Strength and increased vibrational lifetime
Journal of Physical Chemistry B, 2019Co-Authors: Dorota Kossowska, Kwanghee Park, Jun Young Park, Chaiho Lim, Kyungwon Kwak, Minhaeng ChoAbstract:Developing infrared (IR) probes is of great interest in biomolecular imaging and spectroscopy. We report our attempt to improve the IR properties of alkyne-derivatized compounds. The vibrational properties of the alkyne (C≡C) stretch mode of aromatic silylacetylene 1 and aliphatic silylacetylene 2 were studied using Fourier transform infrared and femtosecond IR pump–probe spectroscopies. We find that the insertion of silicon at the position adjacent to the alkyne group, separating it from the compound’s main body, causes an approximately 10-fold increase in the Dipole Strength of the C≡C stretch mode and a lengthening of its vibrational lifetime from 5.6 ps for the acetylenic compound without a silicon atom acting like a thermal insulator to 50.6 and 50.4 ps for 1 and 2, respectively. The enhanced Dipole Strength and the increased lifetime of 1 allowed us to measure the 2D IR spectra for long waiting times up to 450 ps, which suggests that the dynamic observation range of 2D IR spectroscopy with these IR ...
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Rational Design of an Acetylenic Infrared Probe with Enhanced Dipole Strength and Increased Vibrational Lifetime
AMER CHEMICAL SOC, 2019Co-Authors: Dorota Kossowska, Kwanghee Park, Jun Young Park, Chaiho Lim, Kyungwon Kwak, Minhaeng ChoAbstract:Developing infrared (IR) probes is of great interest in biomolecular imaging and spectroscopy. We report our attempt to improve the IR properties of alkyne-derivatized compounds. The vibrational properties of the alkyne (C C) stretch mode of aromatic silylacetylene 1 and aliphatic silylacetylene 2 were studied using Fourier transform infrared and femtosecond IR pump-probe spectroscopies. We find that the insertion of silicon at the position adjacent to the alkyne group, separating it from the compound's main body, causes an approximately 10-fold increase in the Dipole Strength of the C C stretch mode and a lengthening of its vibrational lifetime from 5.6 ps for the acetylenic compound without a silicon atom acting like a thermal insulator to 50.6 and 50.4 ps for 1 and 2, respectively. The enhanced Dipole Strength and the increased lifetime of 1 allowed us to measure the 2D IR spectra for long waiting times up to 450 ps, which suggests that the dynamic observation range of 2D IR spectroscopy with these IR probes can be extended into the subnanosecond range where protein skeletal movements occur. © 2019 American Chemical Societ
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Simultaneous enhancement of transition Dipole Strength and vibrational lifetime of an alkyne IR probe via π-d backbonding and vibrational decoupling
ROYAL SOC CHEMISTRY, 2019Co-Authors: Dorota Kossowska, Kyungwon Kwak, Lee Giseong, Han Hogyu, Minhaeng ChoAbstract:© 2019 the Owner Societies.Alkyne infrared (IR) probes 1-6 with Si and S (or Se) atoms incorporated into the CC bond were synthesized, and the vibrational properties of their CC stretch mode were studied using Fourier transform infrared (FTIR) and femtosecond IR pump-probe (IR PP) spectroscopies in combination with quantum chemical calculations. From FTIR studies, the transition Dipole Strengths (in units of 10-2 D2) of 1-3 having the Si atom were measured to be 1.85, 3.32, and 2.52, whereas those of 4-6 having no Si atom were measured to be 0.13, 0.20, and 0.17, respectively, in CHCl3. Thus, the increase in the transition Dipole Strength of the CC stretch mode upon incorporation of the Si atom into the CC bond is by a factor of about 14 or higher. The large increase in the transition Dipole Strength of the CC stretch mode upon such Si incorporation is attributed to π-d backbonding between the CC group's π and Si atom's d orbitals. From IR PP experiments, the vibrational lifetimes of the CC stretch mode in 1-3 having none, S, and Se atoms were determined to be 5.7 ± 0.7, 13.0 ± 1.1, and 94.2 ± 5.8 ps, respectively, in CHCl3. Thus, the increase in the vibrational lifetime of the CC stretch mode upon incorporation of the S (or Se) atom between the phenyl ring and the CC bond is by a factor of about 2 (or 16) or higher. The large increase in the vibrational lifetime of the CC stretch mode upon such S (or Se) incorporation is attributed to its heavy atom effect impeding vibrational couplings between the CC stretch and phenyl ring vibrations. From two-dimensional infrared (2DIR) experiments, the large transition Dipole Strength and long vibrational lifetime of 3 containing the Si and S (or Se) atoms were shown to enable the measurement of its 2DIR spectra up to 500 ps. The strongly absorbing alkynes with long vibrational lifetimes will be a promising probe of molecular dynamics in nonlinear vibrational spectroscopy and imaging on an extended time scal
V Tselyaev - One of the best experts on this subject based on the ideXlab platform.
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low lying Dipole response in the relativistic quasiparticle time blocking approximation and its influence on neutron capture cross sections
Nuclear Physics, 2009Co-Authors: Elena Litvinova, P Ring, H P Loens, K Langanke, G Martinezpinedo, T Rauscher, F K Thielemann, V TselyaevAbstract:Abstract We have computed Dipole Strength distributions for nickel and tin isotopes within the Relativistic Quasiparticle Time Blocking Approximation (RQTBA). These calculations provide a good description of data, including the neutron-rich tin isotopes 130,132Sn. The resulting Dipole Strengths have been implemented in Hauser–Feshbach calculations of astrophysical neutron capture rates relevant for r-process nucleosynthesis studies. The RQTBA calculations show the presence of enhanced Dipole Strength at energies around the neutron threshold for neutron rich nuclei. The computed neutron capture rates are sensitive to the fine structure of the low lying Dipole Strength, which emphasizes the importance of a reliable knowledge of this excitation mode.
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microscopic description of the low lying and high lying electric Dipole Strength in stable ca isotopes
Physics Letters B, 2007Co-Authors: G Tertychny, V Tselyaev, S Kamerdzhiev, F Grummer, S Krewald, J Speth, A Avdeenkov, Elena LitvinovaAbstract:Abstract The properties of the low lying and high lying electric Dipole Strength in the stable 40Ca, 44Ca and 48Ca isotopes have been calculated within the Extended Theory of Finite Fermi Systems (ETFFS). This approach is based on the random phase approximation (RPA) and includes the single particle continuum as well as the coupling to low lying collective states which are considered in a consistent microscopic way. For 44Ca we also include pairing correlations. We obtain good agreement with the existing experimental data for the gross properties of the low lying and high lying Strength. It is demonstrated that the recently measured A-dependence of the electric Dipole Strength below 10 MeV is well understood in our model: due to the phonon coupling some of the Strength in 48Ca is simply shifted beyond 10 MeV. The predicted fragmentation of the Strength can be investigated in ( e , e ′ ) and ( γ , γ ′ ) experiments. The isovector Dipole Strength below 10 MeV is small in all Ca isotopes. Surprisingly, the proton and neutron transition densities of these low lying electric Dipole states are in phase, which indicate isoscalar structure. We conclude that for the detailed understanding of the structure of excited nuclei e.g. the low lying and high lying electric Dipole Strength an approach like the present one is absolutely necessary.
K Sieja - One of the best experts on this subject based on the ideXlab platform.
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gogny hfb qrpa Dipole Strength function and its application to radiative nucleon capture cross section
Physical Review C, 2018Co-Authors: Stephane Goriely, Stephane Hilaire, S Peru, K SiejaAbstract:Valuable theoretical predictions of nuclear Dipole excitations in the whole nuclear chart are of great interest for different applications, including in particular nuclear astrophysics. Here we extend our large-scale calculations of the $E1$ and $M1$ absorption $\ensuremath{\gamma}$-ray Strength function obtained in the framework of the axially symmetric deformed quasiparticle random-phase approximation (QRPA) based on the finite-range D1M Gogny force to the deexcitation Strength function. To do so, shell-model calculations of the deexcitation Dipole Strength function are performed and their limit at low $\ensuremath{\gamma}$ energies used to complement phenomenologically the QRPA calculations. We compare our final prediction of the $E1$ and $M1$ Strength with available experimental data at low energies and show that a fairly good agreement is obtained. Predictions of the Dipole Strength function for spherical and deformed nuclei within the valley of $\ensuremath{\beta}$ stability as well as in the neutron-rich region are discussed and compared with traditional Lorentzian-type prescriptions. Its impact on the total radiative width as well as radiative neutron and proton capture cross sections is studied.
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low energy Dipole Strength from large scale shell model calculations
Epj Web of Conferences, 2017Co-Authors: K SiejaAbstract:Low energy enhancement of radiative Strength functions has been deduced from experiments in several mass regions of nuclei. Such an enhancement is believed to impact the calculated neutron capture rates which are crucial input for reaction rates of astrophysical interest. Recently, shell model calculations have been performed to explain the upbend of the γ-Strength as due to the M 1 transitions between close-lying states in the quasi-continuum in Fe and Mo nuclei. Beyond mean-↓eld calculations in Mo suggested, however, a non-negligible role of electric Dipole in the low energy enhancement. So far, no calculations of both Dipole components within the same theoretical framework have been presented in this context. In this work we present newly developed large scale shell model appraoch that allows to treat on the same footing natural and non-natural parity states. The calculations are performed in a large sd − pf − gds model space, allowing for 1p{1h excitations on the top of the full pf -shell con↓guration mixing. We restrict the discussion to the magnetic part of the Dipole Strength, however, we calculate for the ↓rst time the magnetic Dipole Strength between states built of excitations going beyond the classical shell model spaces. Our results corroborate previous ↓ndings for the M 1 enhancement for the natural parity states while we observe no enhancement for the 1p{1h contributions. We also discuss in more detail the e↑ects of con↓guration mixing limitations on the enhancement coming out from shell model calculations.
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electric and magnetic Dipole Strength at low energy
Physical Review Letters, 2017Co-Authors: K SiejaAbstract:A low-energy enhancement of radiative Strength functions was deduced from recent experiments in several mass regions of nuclei, which is believed to impact considerably the calculated neutron capture rates. In this Letter we investigate the behavior of the low-energy $\ensuremath{\gamma}$-ray Strength of the $^{44}\mathrm{Sc}$ isotope, for the first time taking into account both electric and magnetic Dipole contributions obtained coherently in the same theoretical approach. The calculations are performed using the large-scale shell-model framework in a full $1\ensuremath{\hbar}\ensuremath{\omega}\text{ }\text{ }sd\text{\ensuremath{-}}pf\text{\ensuremath{-}}gds$ model space. Our results corroborate previous theoretical findings for the low-energy enhancement of the $M1$ Strength but show quite different behavior for the $E1$ Strength.
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electric and magnetic Dipole Strength at low energy
Physical Review Letters, 2017Co-Authors: K SiejaAbstract:: A low-energy enhancement of radiative Strength functions was deduced from recent experiments in several mass regions of nuclei, which is believed to impact considerably the calculated neutron capture rates. In this Letter we investigate the behavior of the low-energy γ-ray Strength of the ^{44}Sc isotope, for the first time taking into account both electric and magnetic Dipole contributions obtained coherently in the same theoretical approach. The calculations are performed using the large-scale shell-model framework in a full 1ℏω sd-pf-gds model space. Our results corroborate previous theoretical findings for the low-energy enhancement of the M1 Strength but show quite different behavior for the E1 Strength.