Inelastic Scattering Measurements Research Articles

Initial State Interaction for the 20Ne + 130Te and 18O + 116Sn Systems at 15.3 AMeV from Elastic and Inelastic Scattering Measurements

Double charge exchange (DCE) reactions could provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To achieve this goal, a detailed description of the reaction mechanism is mandatory. This requires the full characterization of the initial and final-state interactions, which are poorly known for many of the projectile-target systems involved in future DCE studies. Among these, we intend to study the 20Ne + 130Te and 18O + 116Sn systems at 15.3 AMeV, which are particularly relevant due to their connection with the 130Te→130Xe and 116Cd→116Sn double-β decays. We measure the elastic and inelastic scattering cross-section angular distributions and compare them with theoretical calculations performed in the optical model, one-step distorted wave Born approximation, and coupled-channel approaches using the São Paulo double-folding optical potential. A good description of the experimental data in the whole explored range of transferred momenta is obtained provided that couplings with the 21+ states of the projectile and target are explicitly included within the coupled-channel approach. These results are relevant also in the analysis of other quasi-elastic reaction channels in these systems, in which the same couplings should be included.

Neutron Inelastic Scattering Measurements for Na, Ge, Zr, Mo and U

Studies for advanced reactor systems such as sodium-cooled fast reactors designed for recycling of high level waste, accelerator driven systems for transmutation, and systems envisioning the use of the Th/U fuel cycle impose tight requirements on nuclear data for accurate predictions of their operation and safety characteristics. Among the identified needs established by sensitivity studies, neutron inelastic scattering on the main structural materials and actinides and some (n,xn) cross sections for actinides feature prominently. Prompt-gamma spectroscopy and time-of-flight techniques were used to measure (n,xnγ) cross-sections of interest. Experiments were performed at the GELINA neutron time-of-flight facility of IRMM. Results for 235U and 23Na are briefly recalled; pertaining theoretical discussions are mentioned to explain observations concerning 238U. The status of studies on 76Ge, Zr and Mo is also reported.

Role of noncollective excitations in heavy-ion fusion reactions and quasi-elastic scattering around the Coulomb barrier

Despite the supposed simplicity of double-closed shell nuclei, conventional coupled-channels calculations, that include all of the known collective states of the target and projectile, give a poor fit to the fusion cross section for the $^{16}$O + $^{208}$Pb system. The discrepancies are highlighted through the experimental barrier distribution and logarithmic derivative, that are both well defined by the precise experimental fusion data available. In order to broaden our search for possible causes for this anomaly, we revisit this system and include in our calculations a large number of non-collective states of the target, whose spin, parity, excitation energy and deformation paramter are known from high-precision proton inelastic-scattering measurements. Although the new coupled-channels calculations modify the barrier distribution, the disagreemnt with experiment remains both for fusion and for quasi-elastic (QE) scattering. We find that the Q-value distributions for large-angle QE scattering become rapidly more important as the incident energy increases, reflecting the trend of the experimental data. The mass-number dependence of the non-collective excitations is discussed.

Method Developing and Testing for Inelastic Scattering Measurements at the GELINA Facility

Accurate inelastic scattering measurements are of interest to improving modelling and simulation of advanced reactor systems through better nuclear data (OECD-NEA, High priority request list for nuclear data http://www.nea.fr/html/dbdata/hprl/). Two setups are available at IRMM for measurements of inelastic scattering with the (n, n′γ)-technique. The first the GAINS gammaarray for inelastic neutron scattering at a 200 m station consists of eight high purity germanium detectors, has high incident neutron energy resolution and is therefore tailored for inelastic scattering measurements. The second, at a 30 m station was developed by IPHC with the purpose of studying actinides for the Th/U cycle and emphasizing besides (n, n′γ) also (n, 2nγ) reactions. In the recent past a number of efforts were started to investigate the uncertainties and corrections required to obtain reliable results and to investigate the limits of accuracy of this technique. A joint effort is described that has led to an improved understanding of the fission chambers used. In particular, the important corrections to the efficiency for fission fragment loss were investigated.

Antiferromagnetic spin fluctuations in LiFeAs observed by neutron scattering

We report neutron inelastic-scattering measurements on the stoichiometric iron-based superconductor LiFeAs. We find evidence for (i) magnetic scattering consistent with strong antiferromagnetic fluctuations and (ii) an increase in intensity in the superconducting state at low energies, similar to the resonant magnetic excitation observed in other iron-based superconductors. The results do not support a recent theoretical prediction of spin-triplet $p$-wave superconductivity in LiFeAs but instead suggest that the mechanism of superconductivity is similar to that in the other iron-based superconductors.

Quantifying the glue - understanding the initial conditions at RHIC and the LHC

Recent results on the suppression of hadrons at forward rapidities from the STAR collaboration indicate that high gluon densities play an important role in the initial conditions of heavy-ion collisions. The study of these initial conditions is therefore crucial in the next stage of understanding and quantifying the data from RHIC and the LHC. The best way to perform these measurements is through Deep Inelastic Scattering measurements on nuclei. Currently, there are no accelerator facilities which are able to perform this measurement. In this paper, I will outline the latest developments of the eRHIC proposal at BNL as well as preliminary designs of a new detector as well as an assessment of the current detectors (PHENIX and STAR) abilities to run in an eRHIC era.

Spin dynamics of half-dopedLa3∕2Sr1∕2NiO4

We report polarized- and unpolarized-neutron inelastic-scattering measurements of the magnetic excitation spectrum in the spin-charge ordered phase of ${\mathrm{La}}_{3∕2}{\mathrm{Sr}}_{1∕2}\mathrm{Ni}{\mathrm{O}}_{4}$. Up to energies of $\ensuremath{\sim}30\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ we observe broad magnetic modes characteristic of a near checkerboard ordering. A linear spin-wave model for an ideal checkerboard ordering with a single antiferromagnetic exchange interaction ${J}^{\ensuremath{'}}=5.8\ifmmode\pm\else\textpm\fi{}0.5\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ between next-nearest-neighbor spins on ${\mathrm{Ni}}^{2+}$ sites, together with a small $XY$-like single-ion anisotropy, provides a reasonable description of the measured dispersion. Above $30\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ the excitations are not fully consistent with the linear spin-wave model, with modes near the two-dimensional reciprocal space wave vector (0.5, 0.5) having an anomalously large intensity. Furthermore, two additional dispersive modes not predicted by spin-wave theory were observed, both of which are probably magnetic. One disperses away from (0.5, 0.5) in the energy range between $50--56\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$, and the other appears around $(h,k)$ type positions $(h,k=\text{integer})$ in the energy range $31--39\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$. We propose a model in which these anomalous features are explained by the existence of discommensurations in the checkerboard ordering. At low energies there is additional diffuse scattering centred on the magnetic ordering wave vector. We associate this diffuse scattering with dynamic antiferromagnetic correlations between spins attached to the doped holes.

Dynamics of superfluid4Heconfined in xerogel glass

We present neutron inelastic-scattering measurements of superfluid ${}^{4}\mathrm{He}$ in porous xerogel glass. Two-dimensional scattering at all wave vectors is observed. Six pore-filling fractions were studied at constant temperature $T=1.25\mathrm{K}.$ We established the dependence on the pore-filling fraction and on the wave vectors of the energies, widths, and intensities of both the three-dimensional and the two-dimensional phonon-maxon-roton excitations. Comparisons are made with the results of neutron studies of thin helium films and of helium in contrasting porous glasses.

Two-dimensional excitations of superfluid [formula omitted] confined in 72% porosity xerogel

We present neutron inelastic-scattering measurements of the low-energy excitation spectrum of superfluid 4 He confined in porous xerogel glass. In addition to the bulk-like excitation, we also observe a broad peak centred at energies of less than that of the bulk-like peak. The dependence on filling fraction of both peaks has been investigated and we find that the second broad peak exhibits behaviour that is consistent with that of an excitation confined to the high-density liquid layers near the pore walls, i.e. with that of a two-dimensional excitation.

High-resolution neutron-scattering study of the roton in confined superfluid4He

We report high-resolution neutron inelastic-scattering measurements of the roton energy and linewidth of superfluid ${}^{4}\mathrm{He}$ confined in 95% porosity aerogel glass for temperatures $0.08<T<1.2\mathrm{K}.$ The confined roton line shape can be described well by a damped harmonic oscillator (DHO) function, as in the bulk. The energy of the confined roton is essentially temperature independent over this temperature range. The roton linewidth does not exhibit a finite width of greater than 0.1 \ensuremath{\mu}eV at low temperature. This result is in contrast to previous measurements carried out at lower resolution.

Neutrino physics with a muon collider

In the last few years, the idea of a muon accelerator complex has been actively pursued as an option for the next generation lepton collider. The very intense muon source (∼ 10 21 / per year) required for the collider, could provide very intense neutrino beams from muon decay in flight. The neutrino sources could either be the straight sections of the accelerator and the collider ring or a dedicated muon storage ring. In this not I discuss the physics potential of such neutrino sources for neutrino oscillations and Deep Inelastic Scattering measurements.

Charm production at HERA

Measurements of open charm production at HERA are reviewed. The paper covers both photoproduction and Deep Inelastic Scattering measurements from the ZEUS and H1 collaborations.

Vibrational modes in C70: A first-principles study.

The vibrational spectrum of the ${\mathrm{C}}_{70}$ molecule is calculated using first-principles density-functional theory. Our approach is based on a combination of the all-electron local-density-functional method and group-theoretical analysis. The calculated vibrational frequencies of the ${\mathrm{C}}_{70}$ molecule are found to be in good agreement with the experimental data available from Raman, infrared, and neutron inelastic-scattering measurements, and provide useful assignment for dormant modes.

A simple effective interaction for peripheral heavy-ion collisions at intermediate energies

A very simple phenomenological nucleon-nucleon effective interaction is derived by folding-model analyses of 36 sets of heavy-ion elastic-scattering data at energies E/A between 10 and 100 MeV. It is represented by a single Yukawa term with a complex strength that varies slowly with energy. It is appropriate for peripheral collisions at intermediate energies. It is proposed for use in consistent analyses of elastic- and inelastic-scattering measurements. The possible role of spin-orbit coupling in heavy-ion elastic scattering at the higher energies is discussed.

Study of 112Cd via high-resolution [formula omitted] and [formula omitted] reactions and IBA model calculations

High-resolution inelastic-scattering measurements on 112Cd with polarized deuterons (20 MeV) and polarized protons (16 and 65 MeV) provide complete spectroscopic information. Transition moments are obtained from the angular distributions of the cross section and analyzing power in a coupled-channel reaction analysis. The results are compared with interacting boson model predictions aiming to describe intruder states, quadrupole-hexadecapole and quadrupole-octupole excitations.

First-principles study of vibrational modes in icosahedral C60.

The vibrational spectrum of the ${\mathrm{C}}_{60}$ molecule is calculated using first-principles density-functional theory. Our approach is based on a combination of the all-electron local-density functional method with group-theoretical analysis. The calculated vibrational frequencies of the icosahedral ${\mathrm{C}}_{60}$ molecule are found to be in excellent agreement with the experimental data available from Raman, infrared, and neutron inelastic-scattering measurements.

Calculations of generalized oscillator strength for electron-impact excitations of krypton and xenon using a relativistic local-density potential.

The generalized oscillator strength (GOS) of an atom is an essential factor in the differential cross section for inelastic scattering of fast charged particles. Recently, Takayanagi et al. [Phys. Rev. A 41, 5948 (1990)] have obtained the GOS for the excitation of atomic krypton to the 4${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{1/2}$)5s and 4${\mathit{p}}^{5}$${(}^{2}$${\mathit{P}}_{3/2}$)5s states from inelastic-scattering measurements using electron-energy-loss spectroscopy. The present study was undertaken with the twofold objective to determine the results of theoretical computations of the scattering parameters of the above experiment and to examine the suitability of a recently developed relativistic local-density-potential method [M. Vijayakumar, N. Vaidehi, and M. S. Gopinathan, Phys. Rev. A 40, 6834 (1989)] to study atomic-collision processes. Calculations have been done to obtain GOS for electron-krypton and electron-xenon collisions in the squared-momentum-transfer range of 0.01 to 10 atomic units. The well-known theory of Bethe has been used for the determination of the GOS in the first-order Born approximation. The present results are in fair agreement with previous Hartree-Slater and Hartree-Fock calculations and with the experimental data available in the literature. Furthermore, results of the present calculations predict that the GOS goes through a minimum, similar to the ``Cooper minimum'' in the photoabsorption cross section, as a function of the value of the momentum transfer. Experiments at slightly higher values of momentum transfer are suggested to verify the position of this minimum.

Force-constant model for the vibrational modes in C60.

A force-constant model for the vibrational modes in ${\mathrm{C}}_{60}$, based on bond-stretching and angle-bending interactions, is presented. The results of this model are compared with the experimental data available from Raman, infrared, and high-resolution electron-energy-loss spectroscopies, as well as neutron inelastic-scattering measurements. Excellent agreement is obtained between calculation and experiment.

Structural properties of liquid alkali-metal-lead alloys: NaPb, KPb, RbPb, and CsPb.

The structural properties of liquid equiatomic alkali-metal--lead alloys APb, with A=Na, K, Rb, and Cs, have been studied with neutron diffraction. The experimental data are reduced to the neutron-weighted total structure factors S(Q) and radial distribution functions n(r). In all the systems studied, S(Q) is characterized by a first sharp diffraction peak (FSDP) at Q\ensuremath{\sim}1 A\r{} $^{\mathrm{\ensuremath{-}}1}$ and n(r) by structure in the first coordination shell at r=3--4 A\r{}, both features indicating the presence of polyatomic structural units. Two types of structural models have been fitted to the experimental data, both based on consideration of such units: the random packing of structural units model, and the reference interaction site model. The structures of the units are derived from powder-diffraction measurements made with the same instrument on solid polycrystalline samples. Allowing for a slight expansion of the units on melting and using physically reasonable values for the adjustable parameters, both models give satisfactory agreement with the experimental data and are used to give the partial structure factors and pair distribution functions. Inelastic-scattering measurements have been made on one system, liquid KPb, using a spectrometer at the same source. These yield a value for the mean diffusion constant, D=1.2\ifmmode\pm\else\textpm\fi{}0.2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ ${\mathrm{cm}}^{2}$/sec, and a smoothly varying inelastic scattering spectrum with no indication of excitations of a molecular character. The FSDP remains well defined when the inelastic scattering is integrated over small energy transfers, indicating a lifetime of ${10}^{\mathrm{\ensuremath{-}}13}$ sec or longer for the intermediate-range order responsible for this peak.

The Nature of the Structural Transition in K<sub>2</sub>Hg(CN)<sub>4</sub> from Powder Diffraction and Inelastic Scattering Measurements

The Nature of the Structural Transition in K<sub>2</sub>Hg(CN)<sub>4</sub> from Powder Diffraction and Inelastic Scattering Measurements