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The electric dipole strength distribution in 120 Sn has been extracted from proton inelastic scattering experiments at E p = 295 MeV and at forward angles including 0°. It differs from the results of a Sn 120 ( γ , γ ′ ) experiment and peaks at an excitation energy of 8.3 MeV. The total strength corresponds to 2.3(2)% of the energy-weighted sum rule and is more than three times larger than what is observed with the ( γ , γ ′ ) reaction. This implies a strong fragmentation of the E1 strength and/or small ground state branching ratios of the excited 1 − states. [ABSTRACT FROM AUTHOR]

Properties of the first excited state of the nucleus 9Be are discussed based on recent (e,é) and (γ,n) experiments. The parameters of an R-matrix analysis of different data sets are consistent with a resonance rather than a virtual state predicted by some model calculations. The energy and the width of the resonance are deduced. Their values are rather similar for all data sets, and the energy proves to be negative. It is argued that the disagreement between the extracted B(E1) values may stem from different ways of integration of the resonance. If corrected, fair agreement between the (e,é) and one of the (γ,n) data sets is found. A recent (γ,n) experiment at the HIγS facility exhibits larger cross sections close to the neutron threshold which remain to be explained. [ABSTRACT FROM AUTHOR]

Scattering of protons of several hundred MeV is a promising new spectroscopic tool for the study of electric dipole strength in nuclei. A case study of 208Pb shows that, at very forward angles, Jπ = 1- states are strongly populated via Coulomb excitation. A separation from nuclear excitation of other modes is achieved by a multipole decomposition analysis of the experimental cross sections based on theoretical angular distributions calculated within the quasiparticle-phonon model. The B(El) transition strength distribution is extracted for excitation energies up to 9 MeV; that is, in the region of the so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows sensitivity to the underlying structure of the £ 1 transitions, which allows for the first time an experimental extraction of the electromagnetic transition strength and the energy centroid of the PDR. [ABSTRACT FROM AUTHOR]

Abstract: Some aspects of the importance of neutrino-induced reactions on nuclei within supernova physics are discussed. It is argued that important constraints on the experimentally unknown cross sections can be obtained from experimental studies of the nuclear response in selected cases. Examples are neutral-current-induced reactions on -shell nuclei extracted from high-resolution inelastic electron scattering data providing the strength distributions and the Gamow–Teller strength in the exotic heavy, odd–odd nuclei 138La and 180Ta deduced from the (3He, ) charge-exchange reaction at zero degree. [Copyright &y& Elsevier]

The validity of the Brink-Axel hypothesis, which is especially important for numerous astrophysical calculations, is addressed for 116, 120, 124 Sn below the neutron separation energy by means of three independent experimental methods. The-ray strength functions (GSFs) extracted from primary?-decay spectra following charged-particle reactions with the Oslo method and with the shape method demonstrate excellent agreement with those deduced from forward-angle inelastic proton scattering at relativistic beam energies. In addition, the GSFs are shown to be independent of excitation energies and spins of the initial and final states. The results provide a critical test of the generalized Brink-Axel hypothesis in heavy nuclei, demonstrating its applicability in the energy region of the pygmy dipole resonance. [ABSTRACT FROM AUTHOR]

The dipole polarizability of stable even-mass tin isotopes 112,114,116,118,120,124Sn was extracted from inelastic proton scattering experiments at 295 MeV under very forward angles performed at RCNP. Predictions from energy density functionals cannot account for the present data and the polarizability of 208Pb simultaneously. The evolution of the polarizabilities in neighboring isotopes indicates a kink at 120Sn while all model results show a nearly linear increase with mass number after inclusion of pairing corrections. [ABSTRACT FROM AUTHOR]

The gamma strength function and level density of 1- states in 96Mo have been extracted from a high-resolution study of the (p, p′) reaction at 295 MeV and extreme forward angles. By comparison with compound nucleus γ decay experiments, this allows a test of the generalized Brink-Axel hypothesis in the energy region of the pygmy dipole resonance. The Brink-Axel hypothesis is commonly assumed in astrophysical reaction network calculations and states that the gamma strength function in nuclei is independent of the structure of the initial and final state. The present results validate the Brink-Axel hypothesis for 96Mo and provide independent confirmation of the methods used to separate gamma strength function and level density in γ decay experiments. [ABSTRACT FROM AUTHOR]

Background: γ strength functions (GSFs) and level densities (LDs) are essential ingredients of statistical nuclear reaction theory with many applications in astrophysics, reactor design, and waste transmutation. Purpose: The aim of the present work is a test of systematic parametrizations of the GSF recommended by the RIPL-3 database for the case of 208Pb. The upward GSF and LD in 208Pb are compared to γ decay data from an Oslo-type experiment to examine the validity of the Brink-Axel (BA) hypothesis. Methods: The E1 and M1 parts of the total GSF are determined from high-resolution forward angle inelastic proton scattering data taken at 295 MeV at the Research Center for Nuclear Physics (RCNP), Osaka, Japan. The total LD in 208Pb is derived from the 1-LD extracted with a fluctuation analysis in the energy region of the isovector giant dipole resonance. Results: The E1 GSF is compared to parametrizations recommended by the RIPL-3 database showing systematic deficiencies of all models in the energy region around neutron threshold. The new data for the poorly known spin-flip M1 resonance call for a substantial revision of the model suggested in RIPL-3. The total GSF derived from the present data is larger in the PDR energy region than the Oslo data but the strong fluctuations due to the low LD resulting from the double shell closure of 208Pb prevent a conclusion on a possible violation of the BA hypothesis. Using the parameters suggested by RIPL-3 for a description of the LD in 208Pb with the back-shifted Fermi gas model, remarkable agreement between the two experiments spanning a wide excitation energy range is obtained. Conclusions: Systematic parametrizations of the E1 and M1 GSF parts need to be reconsidered at low excitation energies. The good agreement of the LD provides an independent confirmation of the approach underlying the decomposition of GSF and LD in Oslo-type experiments. [ABSTRACT FROM AUTHOR]

The 112,120Sn() reactions were studied for different endpoint energies of the incident bremsstrahlung spectrum below the neutron separation energies at the superconducting Darmstadt electron linear accelerator S-DALINAC. Dipole transition strength distributions have been extracted for 112Sn; the analysis of 120Sn is still in progress. In the case of 112Sn a concentration of dipole excitations is observed between 5 and . Combining with existing data for 116,124Sn provides a systematics of the pygmy dipole resonance (PDR) in stable Sn nuclei which serves as a benchmark test of recent microscopic calculations aiming at a description of the PDR in exotic neutron-rich Sn isotopes. [Copyright &y& Elsevier]

Abstract: The neutron spectroscopic factor of the 7He ground state is extracted from an R-matrix analysis of a recent measurement of the 7Li(d, 2He)7He reaction with good energy resolution. The width extracted from a deconvolution of the spectrum is (full width at half maximum, FWHM). The result is slightly larger than predictions of recent ‘ab initio’ Green''s function Monte Carlo and fermionic molecular dynamics calculations. [Copyright &y& Elsevier]

Quasiparticle random-phase approximation calculations, where rotational, translational and Galilean invariance are restored selfconsistently by using separable effective forces, are presented for the ground state dipole response in the even-mass isotopes 122–130Te. The simultaneous description of E1 and M1 transitions permits a direct comparison with nuclear resonance fluorescence experiments. The extracted properties of the scissors mode reveal a considerable complexity in these near closed-shell nuclei: neither approaches successful in deformed nuclei nor a two-phonon picture suggested near shell closures nor the interacting boson model can fully account for the data. [Copyright &y& Elsevier]

Abstract: A new experimental method for a precise determination of the proton charge radius with elastic electron proton scattering at low momentum transfers is shown to be feasible, using a novel technique where the recoil protons are detected in a set of Si detectors. [Copyright &y& Elsevier]

Experiments investigating the fine structure of the Isovector Giant Dipole Resonances (IVGDR) have been carried out on target nuclei 40,42,44,48Ca with 200 MeV proton inelastic scattering reactions using the high-energy resolution capability and the zero-degree set-up at the K600 magnetic spectrometer of the iThemba LABS, Cape Town, South Africa. Quasi-free scattering background contributions in the experimental data have been removed by applying a novel method of Discrete Wavelet Transform (DWT) analysis. Energy scales extracted are compared with the state-of-the-art theoretical calculations within the framework of the Quasiparticle- RPA and Relativistic Quasiparticle Time Blocking Approximation (RQTBA). For 40,48Ca, these calculations consider all major processes (Landau damping, escape width, spreading width) contributing to the damping of the IVGDR. [ABSTRACT FROM AUTHOR]

Proton inelastic scattering experiments at energy E p = 200 MeV and a spectrometer scattering angle of 0° were performed on 144,146,148,150 Nd and 152 Sm exciting the IsoVector Giant Dipole Resonance (IVGDR). Comparison with results from photo-absorption experiments reveals a shift of resonance maxima towards higher energies for vibrational and transitional nuclei. The extracted photo-absorption cross sections in the most deformed nuclei, 150 Nd and 152 Sm, exhibit a pronounced asymmetry rather than a distinct double-hump structure expected as a signature of K -splitting. This behaviour may be related to the proximity of these nuclei to the critical point of the phase shape transition from vibrators to rotors with a soft quadrupole deformation potential. Self-consistent random-phase approximation (RPA) calculations using the SLy6 Skyrme force provide a relevant description of the IVGDR shapes deduced from the present data. [ABSTRACT FROM AUTHOR]

Inelastic proton scattering at energies of a few hundred million electron volts and extreme forward angles selectively excite the isovector spin-flip M1 (IVSM1) resonance. A method based on isospin symmetry is presented to extract its electromagnetic transition strength from the (p,p') cross sections. It is applied to 48Ca, a key case for an interpretation of the quenching phenomenon of the spin-isospin response, and leads to a M1 strength consistent with an older (e,e') experiment excluding the almost two times larger value from a recent (γ,n) experiment. Good agreement with electromagnetic probes is observed in 208Pb, suggesting the possibility of extracting systematic information on the IVSM1 resonance in heavy nuclei. [ABSTRACT FROM AUTHOR]

The fine structure of the IsoVector Giant Dipole Resonance (IVGDR) in the doubly-magic nuclei 40,48Ca observed in inelastic proton scattering experiments under 0 ∘ is used to investigate the role of different mechanisms contributing to the IVGDR decay width. Characteristic energy scales are extracted from the fine structure by means of wavelet analysis. The experimental scales are compared to different theoretical approaches allowing for the inclusion of complex configurations beyond the mean-field level. Calculations are performed in the framework of RPA and beyond-RPA in a relativistic approach based on an effective meson-exchange interaction, with the UCOM effective interaction and, for the first time, with realistic two- plus three-nucleon interactions from chiral effective field theory employing the in-medium similarity renormalization group. All models highlight the role of Landau fragmentation for the damping of the IVGDR, while the differences in the coupling strength between one particle-one hole (1p-1h) and two particle-two hole (2p-2h) correlated (relativistic) and non-correlated (non-relativistic) configurations lead to very different pictures of the importance of the spreading width resulting in wavelet scales being a sensitive measure of their interplay. The relativistic approach with particle-vibration coupling, in particular, shows impressive agreement with the number and absolute values of the scales extracted from the experimental data. [ABSTRACT FROM AUTHOR]

Differential cross sections of isoscalar and isovector spin-M1 (P+ → 1+) transitions are measured using high-energy-resolution proton inelastic scattering at Ep = 295 MeV on 24Mg, 28Si, 32S, and 36Ar at 0°-l 4°. The squared spin-M1 nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to Ex = 16 MeV compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-M1 transitions, respectively. Thus, no quenching is observed for isoscalar spin-M1 transitions, while the matrix elements for isovector spin-M1 transitions are quenched by an amount comparable with the analogous Gamow-Teller transitions on those target nuclei. [ABSTRACT FROM AUTHOR]

The electric dipole strength distribution in 120Sn between 5 and 22 MeV has been determined at the Research Center for Nuclear Physics, Osaka, from polarization transfer observables measured in proton inelastic scattering at E0 = 295 MeV and forward angles including 0°. Combined with photoabsorption data, a highly precise electric dipole polarizability αD(120Sn) = 8.93(36) fm3 is extracted. The dipole polarizability as isovector observable par excellence carries direct information on nuclear symmetry energy and its density dependence. The correlation of the new value with the well-established αD(208Pb) serves as a test of its prediction by nuclear energy density functionals. Models based on modern Skyrme interactions describe the data fairly well while most calculations based on relativistic Hamiltonians cannot. [ABSTRACT FROM AUTHOR]

The 112,l20Sn(y,y') 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 112Sn up to 9.5 MeV and for 120Sn 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. [ABSTRACT FROM AUTHOR]

The article presents a study which was carried out to analyze low energy dipole strength in Tin (Sn) isotopes. Topics discussed include conduct of the study at the superconducting Darmstadt electron linear accelerator S-DALINAC, extraction of dipole strength distributions for Tin isotopes, and application of fluctuation analysis to the photon scattering spectra. Other topics discussed include use of relativistic time blocking approximation method and quasiparticle-phonon model in the study.

The article discusses a study to determine [112,120]Tin (Sn) reactions below the neutron separation energies at the superconducting Darmstadt, Germany, electron linear accelerator S-DALINAC for different endpoint energies. Topics discussed include electric pygmy dipole resonance in atomic nuclei, dipole strength in context with neutron thresholds which may lead to changes of neutron-capture rates in the astrophysical processes, and photoexcitation of nuclear levels.

The article presents a study on dipole strength in isotopes of tin (Sn). Topics discussed include study of the [112,120] Sn( 훾 , 훾 ') reactions below the neutron separation energies at the superconducting Darmstadt electron linear accelerator S-DALINAC, application of a fluctuation analysis to the photon scattering spectra and model approaches such as the quasiparticle-phonon model and the relativistic time blocking approximation.

The article discusses the Low-energy dipole strength in Tin (Sn). Topics discussed include studying the neutron separation energies at the superconducting Darmstadt electron linear accelerator, observing the concentration of dipole excitations in nuclei, and electric pygmy dipole resonance (PDR) in nuclei.

The article presents brief information on low-energy dipole strength in isotopes of tin. It talks about the neutron separation energies that are examined at the superconducting Darmstadt electron linear accelerator S-DALINAC for various energies of the incident bremsstrahlung spectrum. Information on Dipole strength distributions, photon scattering spectra, and quasiparticle-phonon model, is also discussed.

Background: The electric isovector giant dipole resonance (IVGDR) in 208Pb has been measured with high energy resolution with the (p,p') reaction under extreme forward angles [A. Tamii et al., Phys. Rev. Lett. 107, 062502 (2011)] and shows considerable fine structure. Purpose: The aim of the present work is to extract scales characterizing the observed fine structure and to relate them to dominant decay mechanisms of giant resonances. Furthermore, the level density of Jπ=1- states is determined in the energy region of the IVGDR. Methods: Characteristic scales are extracted from the spectra with a wavelet analysis based on continuous wavelet transforms. Comparison with corresponding analyses of B(E1) strength distributions from microscopic model calculations in the framework of the quasiparticle phonon model and the relativistic random phase approximation allows one to identify giant resonance decay mechanisms responsible for the fine structure. The level density of 1- states is related to local fluctuations of the cross sections in the energy region of the IVGDR, where contributions from states with other spin parities can be neglected. The magnitude of the fluctuations is determined by the autocorrelation function. Results: Scales in the fine structure of the IVGDR in 208Pb are found at 80, 130, 220, 430, 640, and 960 keV, and at 1.75 MeV. The values of the most prominent scales can be reasonably well reproduced by the microscopic calculations although they generally yield a smaller number of scales. The inclusion of complex configurations in the calculations changes the E1 strength distributions but the impact on the wavelet power spectra and characteristic scales is limited. The level density of 1- states is extracted in the excitation energy range 9-12.5 MeV and compared to a variety of phenomenological and microscopic models. Conclusions: In both models the major scales are already present at the one-particle one-hole level indicating Landau damping as a dominant mechanism responsible for the fine structure of the IVGDR in contrast to the isoscalar giant quadrupole resonance, where fine structure arises from the coupling to low-lying surface vibrations. The back-shifted Fermi gas model parametrization of Rauscher et al., Phys. Rev. C 56, 1613 (1997) describes the level-density data well, while other phenomenological and microscopic approaches fail to reproduce absolute values or the energy dependence or both. [ABSTRACT FROM AUTHOR]

The low-lying dipole strength of the N = 28 closed-shell nucleus 52Cr was studied with nuclear resonance fluorescence up to 9.9 MeV, using bremsstrahlung at the superconducting Darmstadt linear electron accelerator S-DALINAC. Twenty-eight spin-1 states were observed between 5.0 and 9.5 MeV excitation energy, 14 of which for the first time. Both electric dipole excitations (E1, around 8 MeV) and magnetic dipole excitations (A/1, around 9 MeV) were detected. Microscopic calculations within the quasiparticle-phonon nuclear model were performed and show good agreement with experimental results. The structure of E1 and M1 excitations, respectively, is discussed. [ABSTRACT FROM AUTHOR]

The level density of 2+ states in 40Ca has been extracted in the energy region of the isoscalar giant quadrupole resonance from a fluctuation analysis of high-energy-resolution (p, p') data taken at incident energies of 200 MeV at the K600 magnetic spectrometer of iThemba LABS, South Africa. Quasifree-scattering cross sections were calculated to estimate their role as a background contribution to the spectra and found to be small. The shape of the background was determined from the discrete wavelet transform of the spectra using a biorthogonal wavelet function normalized at the lowest particle separation threshold. The experimental results are compared to widely used phenomenological and microscopic models. [ABSTRACT FROM AUTHOR]

Abstract: The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in 40Ca has been investigated in high energy-resolution experiments using proton inelastic scattering at . Fine structure is observed in the region of the ISGQR and its characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The experimental scales are well described by Random Phase Approximation (RPA) and second-RPA calculations with an effective interaction derived from a realistic nucleon–nucleon interaction by the Unitary Correlation Operator Method (UCOM). In these results characteristic scales are already present at the mean-field level pointing to their origination in Landau damping, in contrast to the findings in heavier nuclei and also to SRPA calculations for 40Ca based on phenomenological effective interactions, where fine structure is explained by the coupling to two-particle–two-hole (2p–2h) states. [Copyright &y& Elsevier]

Abstract: Fission of 238U and 234U induced by bremsstrahlung of 6.5–9.0 MeV endpoint energy has been investigated at the superconducting Darmstadt electron linear accelerator S-DALINAC. Using a twin Frisch grid ionization chamber, fission-fragment energy and mass distributions have been determined by means of the double kinetic-energy technique. Results on the fission-fragment characteristics from are in agreement with results from the literature. In addition fission-fragment mass and energy distributions from are presented for the first time in this energy region. An analysis of fission modes within the Brosa model has been performed. The relative yield of the S1 mode was found to be in 234U and in 238U. [ABSTRACT FROM AUTHOR]

Abstract: At the continuous wave (cw) Superconducting Darmstadt Electron Linear Accelerator S-DALINAC, a new method has been developed for the determination of the electric () and magnetic () polarizabilities of the proton and the deuteron. For that purpose the energy and angular dependence of the differential cross-section for elastic and scattering of bremsstrahlung photons in the energy range between 20 and 100MeV is measured by detecting the recoiling proton (deuteron) in coincidence with the scattered bremsstrahlung photon. and are then found by means of a best fit to a theoretical description of the scattering cross-section with these quantities as open parameters. The experimental setup consists of a bremsstrahlung photon facility, two specially designed high pressure hydrogen (deuterium) ionization chambers which serve as targets and detectors of the recoil proton (deuteron), NaI gamma spectrometers and several additional detectors for beam diagnostics and normalization. The whole setup was tested using bremsstrahlung photon beams with endpoint energies of 60 and 79.3MeV. The results of the test experiments show that future high-statistics measurements are feasible. [Copyright &y& Elsevier]

Abstract: The photon scattering reaction has been studied with the nearly monochromatic, linearly polarized photon beams at the High Intensity γ-ray Source (HIγS) at the DFELL. Azimuthal scattering intensity asymmetries measured with respect to the polarization plane of the beam have been used for the first time to assign both the spin and parity quantum numbers of dipole excited states of 206,207,208Pb at excitation energies in the vicinity of 5.5 MeV. Evidence for dominant particle–core coupling is deduced from these results along with information on excitation energies and electromagnetic transition matrix elements. Implications of the existence of weakly coupled states built on highly excited core states in competition with single particle (hole) excitations at comparable energies are discussed. [Copyright &y& Elsevier]

Abstract: We have calculated the M1 strength distributions in the 36,38Ar isotopes within large-scale shell model studies which consider valence nucleons in the sd and pf shells. While the M1 strength in 36Ar is well reproduced within the sd shell, the experimentally observed strong fragmentation of the M1 strength in 38Ar requires configuration mixing between the sd and the pf shells adding to our understanding of correlations across the shell gap. [Copyright &y& Elsevier]

We present spin- and parity-resolved level densities extracted from high-resolution hadron and electron scattering data by means of a fluctuation analysis. A nearly model-independent method based on discrete wavelet transform is introduced for the determination of a non-resonant background. The data obtained are compared to the predictions of two models widely used in applications for astrophysical network calculations with an emphasis on a possible parity dependence of nuclear level densities. [Copyright &y& Elsevier]

High-resolution inelastic electron scattering experiments at the S-DALINAC and proton scattering experiments at iThemba LABS permit a thorough test of the nature of proposed one- and two-phonon symmetric and mixed-symmetric 2+ states of the nucleus 94Mo. The combined analysis reveals the one-phonon content of the mixed-symmetry state and its isovector character suggested by microscopic calculations. The purity of two-phonon 2+ states is extracted. [Copyright &y& Elsevier]