Quasielastic Peak Research Articles

Simple qualitative description of EMC ratiosμAfor0.2≲x≲1.5and some sample calculations

We study EMC ratios on the basis of a relation between Structure Functions (SF) for a nucleus and for a nucleon, which is governed by a SF f^{PN,A}(x,Q^2) of an unphysical nucleus, composed of point-nucleons. We demonstrate that the characteristic features of EMC ratios \mu^A are determined by the above f^{PN,A} and the SF of free nucleons. We account for the positions of the points x_{1,2} in the interval 0.2 <~ x <~ 0.9, where \mu^A(x,Q^2)=1 and also for the minimum x_m in that interval. We similarly describe the oscillations in \mu^A for Q^2 <~ (3.5-4.0) GeV^2 in the Quasi-Elastic peak region 0.95 <~ x <~ 1.05 and for its subsequent continuous increase up to x\approx 1.4. Finally we compute \mu^A over the entire range above for A=^4He, C, Fe and Au and several Q^2 values. The results are in reasonable agreement with both directly measured and indirectly extracted data.

Improved(e,e')response functions at intermediate momentum transfers: TheHe3case

A possibility of extending the applicability range of non-relativistic calculations of electronuclear response functions in the quasielasic peak region is studied. We show that adopting a particular model for determining the kinematical inputs of the non-relativistic calculations can extend this range considerably, almost eliminating the reference frame dependence of the results. We also show that there exists one reference frame, where essentially the same result can be obtained with no need of adopting the particular kinematical model. The calculation is carried out with the Argonne V18 potential and the Urbana IX three-nucleon interaction. A comparison of these improved calculations with experimental data shows a very good agreement for the quasielastic peak positions at $q=500,$ 600, 700 MeV/c and for the peak heights at the two lower $q$--values, while for the peak height at $q=700$ MeV/c one finds differences of about 20%.

Dynamics of the Singlet–Triplet System Coupled with Conduction Spins –Application to Pr Skutterudites–

Dynamics of the singlet-triplet crystalline electric field (CEF) system at finite temperatures is discussed by use of the non-crossing approximation. Even though the Kondo temperature is smaller than excitation energy to the CEF triplet, the Kondo effect appears at temperatures higher than the CEF splitting, and accordingly only quasi-elastic peak is found in the magnetic spectra. On the other hand, at lower temperatures the CEF splitting suppresses the Kondo effect and inelastic peak develops. The broad quasi-elastic neutron scattering spectra observed in PrFe_4P_{12} at temperatures higher than the quadrupole order correspond to the parameter range where the CEF splittings are unimportant.

Effect of semiclassical molecular initial ground state configuration on the neutron spectra in the interactions ofp+Al,Fe, andZrat 1.2 GeV

We studied the effect of the semiclassical molecular initial ground state configuration of the nucleus on the neutron spectra for $p+\mathrm{Al},\phantom{\rule{0.3em}{0ex}}\mathrm{Fe}$, and $\mathrm{Zr}$ at 1.2 GeV by using an improved ultrarelativistic quantum molecular dynamics (ImUrQMD) model. Compared to the standard UrQMD version, it incorporates: (i) Pauli potential, (ii) a medium modified $\mathrm{NN}\ensuremath{\rightarrow}N\ensuremath{\Delta}$ angular distribution, and (iii) a statistical multifragmentation decay model as an afterburner. It is shown that the slow evaporated, cascade, and quasielastic (inelastic) peaks of neutrons are all sensitive to different initialization procedures. Therefore, the implementation of a proper semiclassical ground state initialization in the ImUrQMD model is of importance for the description of all the neutron spectra in proton-induced reactions at intermediate energies $(\ensuremath{\approx}1\mathrm{GeV})$.

The longitudinal and transverse nuclear responses within the RPA framework

The longitudinal and transverse nuclear responses to inclusive electron scattering reactions are analysed within the random phase approximation (RPA) framework. Several residual interactions are considered and it is shown that the exchange terms in the RPA make it very difficult to find an effective residual interaction capable of reproducing simultaneously the quasielastic peak of both the longitudinal and transverse responses. By means of a simplified model it is illustrated that the residual interaction used in a ring approximation must fulfil some restrictions in order to qualitatively reproduce the full RPA results.

Disorder-Induced Polaron Formation in the Magnetoresistive PerovskiteLa0.54Ba0.46MnO3

Neutron studies of the effect of A-site chemical disorder on the ferromagnetic transition and spin dynamics for the magnetoresistive perovskite La0.54Ba0.46MnO3 are reported. The low temperature spin waves reveal that disorder reduces exchange interactions by only 9%. The development of a quasielastic peak in the spectrum below TC and long-time relaxation of the order parameter indicate that the transition is discontinuous in the disordered sample, while it appears continuous for the ordered sample. These results strongly suggest that chemical disorder lowers the energy for polaron formation in manganese perovskites, and is the origin of the dramatic 50 K reduction in TC.

Measurement of the ExclusiveH3e(e,e′p)Reaction Below the Quasielastic Peak

New, high-precision measurements of the H3e(e,e′p) reaction using the A1 Collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at energy transfers below the quasielastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on the plane wave impulse approximation were observed in both the two- and three-body breakup channels. Full Faddeev-type calculations account for some of the observed excess cross-section, but significant differences remain.Received 27 March 2002DOI:https://doi.org/10.1103/PhysRevLett.93.132301©2004 American Physical Society

Reply to "Comment on 'Collective dynamics in liquid lithium, sodium, and aluminum' ".

Phys. Rev. E 70, 013201 (2004)]] have raised certain objections to physical interpretation of the parameters of the model proposed by us earlier [Phys. Rev. E 67, 012201 (2003)]]. We have found that heat diffusion term enters into processes which are responsible for the quasielastic peak of the dynamical structure factor. An attempt has been made to study the role played by atomic and electronic contributions to thermal conductivity for studying atomic density-density correlation function.

Influence of medium modified angular distributions and mean field on the quasielastic and inelastic peaks of neutrons induced by1.2GeVprotons on targets with27⩽A⩽232

An analysis of the quasielastic and inelastic peaks of neutrons induced by 1.2 GeV protons on targets with 27{<=}A{<=}232 is presented using the ultrarelativistic quantum molecular dynamics (UrQMD) model. Two distinct contributions of the nuclear medium are studied in the UrQMD framework, referred to as 'in-medium' and 'mean field' effects. The former only includes modifications to the NN-elastic and NN{yields}N{delta} angular distributions as well as changes to the {delta}-mass distribution. The latter incorporates the (QMD) interaction potential between nucleons. It is shown that in-medium effect produces an important role for enhancing the quasi-inelastic peak, while the mean field effect enhances the intensity of both peaks and becomes important in the quasielastic region. The introduction of both effects in the UrQMD calculations improves the intensity and location of the quasielastic and inelastic peaks. A rather smooth dependence of the integrated cross sections of the quasielastic and inelastic peaks on the mass number at both angles is also found and shown to be in qualitative agreement with the UrQMD incorporating these two effects.

Quasielastic and low vibrational lineshapes in atom–surface diffusion

The diffusion and low frequency vibrational motions of atoms and molecules onsurfaces can be measured by means of quasielastic helium atom scattering. In thispaper, we discuss and investigate different analytical approximations, based on thetheory of stochastic processes, to the dynamic structure factor, considering thetwo motions on an equal footing. Special emphasis is put on the nature of thecorresponding lineshapes, explained in terms of the motional narrowing effect. We alsodiscuss the influence of the diffusional and vibrational coupling and several ways ofexperimentally separating the two types of contributions to the dynamic structure factor.In particular, we propose that the so-called inelastic focusing singularity fromatom–surface scattering controls the lineshapes of quasielastic and vibrational peaks.

Role of 2p–2h MEC excitations in superscaling

Following recent studies of inclusive electron scattering from nuclei at high energies which focused on two-nucleon emission mediated by meson-exchange currents, in this work the superscaling behavior of such contributions is investigated. Comparisons are made with existing data below the quasielastic peak where at high momentum transfers scaling of the second kind is known to be excellent and scaling of the first kind is good, in the proximity of the peak where both 1p–1h and 2p–2h contributions come into play, and above the peak where inelasticity becomes important and one finds scaling violations of the two kinds.

Effects of isospin and energy dependences of the nuclear mean field in spallation reactions

In many applications of the intranuclear-cascade (INC) model to spallation reactions, all nucleons in the target are assumed to move in a common potential well. However, the potential depth should depend upon nucleon isospin and energy. The present paper describes the first results obtained after the introduction of these features in the Liege INCL3 model. It is shown that such modifications change cascade particle multiplicities significantly but total particle multiplicities are only slightly altered. Nucleon inclusive cross-sections are not modified significantly, except in the region of the quasi-elastic peaks. In particular, the centroid of the peak in neutron double differential cross-sections relative to proton-induced reactions can be sizeably shifted toward larger energy losses, as is observed experimentally. Implications of these results are discussed.

Polarization transfer and spin response functions of theH2(p⃗,n⃗)reaction at345MeV

Differential cross sections and a complete set of polarization observables have been measured in the quasielastic $^{2}\mathrm{H}(p,n)$ reaction at a bombarding energy of $345\phantom{\rule{0.3em}{0ex}}\text{MeV}$ and laboratory scattering angles of $16\ifmmode^\circ\else\textdegree\fi{}$, $22\ifmmode^\circ\else\textdegree\fi{}$, and $27\ifmmode^\circ\else\textdegree\fi{}$. The data are compared with plane-wave impulse approximation calculations employing an optimal factorization approximation. The agreement between the experimental and theoretical results validates these approximations in the present momentum- and energy-transfer regions. The experimental spin-longitudinal and spin-transverse response functions, ${R}_{L}$ and ${R}_{T}$, respectively, are deduced from the data. The obtained ${R}_{T}$ is consistent with that obtained from the quasielastic electron scattering. The theoretical calculations with the Reid soft core potential give good descriptions for ${R}_{L}$ and ${R}_{T}$, whereas the latter is slightly underestimated around the quasielastic peak.

Magnetic effects in resonant X-ray emission spectroscopy

A theoretical description for L α and L β emission spectra recorded at different excitation photon energies gives the main spectral lines: a normal emission peak, with the constant energy, and a quasi-elastic peak that moves in energy scale when the incident photon energy changes. The intensity of the quasi-elastic peak is strongly controlled by valence electron excitations due to core-hole effects. Characteristic shake-up processes give rise to double lines in spectra. Applications of resonant inelastic soft X-ray scattering for studying magnetic systems are discussed. Emission spectra (as well as absorption spectra) show the magnetic dichroism when they are excited by the polarized incident X-ray radiation. But, the emission experiments contain information on the local magnetic moment values on excited atoms even in the case of depolarized incident radiation and in disordered magnetic states. The integral intensities ratio for L β / L α lines in transition metal oxides are analyzed from this point of view. The similarity of experimental X-ray fluorescent spectra with emission spectra received by electron impacts allow us to conclude that in 3d-element compounds the high-energy electron impact transfers the 2p-electron into valence states with considerable probability.

First-order transition in the itinerant ferromagnetCoS1.9Se0.1

Undoped CoS$_2$ is an isotropic itinerant ferromagnet with a continuous or nearly continuous phase transition at $T_{\rm C} = 122$ K. In the doped CoS$_{1.9}$Se$_{0.1}$ system, the Curie temperature is lowered to $T_{\rm C} = 90$ K, and the transition becomes clearly first order in nature. In particular we find a discontinuous evolution of the spin dynamics as well as strong time relaxation in the ferromagnetic Bragg intensity and small angle neutron scattering in vicinity of the ferromagnetic transition. In the ordered state the long-wavelength spin excitations were found to be conventional ferromagnetic spin-waves with negligible spin-wave gap ($ < 0.04$ meV), indicating that this system is also an excellent isotropic (soft) ferromagnet. In a wide temperature range up to $0.9T_{\rm C}$, the spin-wave stiffness $D(T)$ follows the prediction of the two-magnon interaction theory, $D(T) = D(0)(1 - AT^{5/2})$, with $D(0) = 131.7 \pm 2.8$ meV-\AA$^{2}$. The stiffness, however, does not collapse as $T \to T_{\rm C}$ from below. Instead a quasielastic central peak abruptly develops in the excitation spectrum, quite similar to results found in the colossal magnetoresistance oxides such as (La-Ca)MnO$_3$.

Influence of the periodic potential shape on the Fokker–Planck dynamics

The influence of the periodic potential structure on the diffusion mechanism of a Brownian particle is studied using the Fokker–Planck equation. The equation is solved numerically by the matrix continued fraction method in order to calculate relevant correlation functions. In particular, jump length probability, diffusion coefficient and the half-width of the quasi-elastic peak of the dynamical structure factor S( q, ω) are fully studied in a wide range of physical parameters for two forms of periodic potential (bistable and metastable potential). There is some difference between results provided by these two potential models, indicating that dynamical properties are very sensitive to the structure of the periodic potential, especially in the low friction regime.

The 2p–2h electromagnetic response in the quasielastic peak and beyond

The contribution to the nuclear transverse response function R T arising from two particle–two hole (2p–2h) states excited through the action of electromagnetic meson exchange currents (MEC) is computed in a fully relativistic framework. The MEC considered are those carried by the pion and by Δ degrees of freedom, the latter being viewed as a virtual nucleonic resonance. The calculation is performed in the relativistic Fermi gas model in which Lorentz covariance can be maintained. All 2p–2h many-body diagrams containing two pionic lines that contribute to R T are taken into account and the relative impact of the various components of the MEC on R T is addressed. The non-relativistic limit of the MEC contributions is also discussed and compared with the relativistic results to explore the role played by relativity in obtaining the 2p–2h nuclear response.

Interpretation of the neutron double-differential cross sections in the interactions ofp+Al,Fe, and Zr at 1.2 GeV using the ultrarelativistic quantum molecular dynamics model

The ultrarelativistic quantum molecular dynamics (UrQMD) model is incorporated with a statistical decay model aiming to describe the neutron double global-differential cross sections of $p+\mathrm{Al},$ Fe, and Zr at 1.2 GeV. Good agreement is generally obtained with the default UrQMD parameters. In particular, the UrQMD calculation with a momentum dependent Pauli potential improves the intensity of the quasielastic peak in neutron double-differential cross sections. The lower and higher energy parts of the neutron spectra at backward angles are found to be sensitive to meson-meson and meson-baryon interactions. The influence of sequential evaporation and simultaneous multifragmentation disintegration mechanisms on the neutron spectra is also investigated. It is shown that the statistical multifragmentation model is more suited for the description of the lower part of the neutron energy spectra.

Microscopic dynamics of liquid aluminum oxide.

Collective excitations have been observed in liquid aluminum oxide at high temperatures by combining a containerless sample environment with inelastic x-ray scattering. The excitation spectra show a well-defined triplet peak structure at lower wave vectors Q (1 to 6 nanometers-1) and a single quasi-elastic peak at higher Q. The high-Q spectra are well described by kinetic theory. The low-Q spectra require a frequency-dependent viscosity and provide previously unknown experimental constraints on the behavior of liquids at the interface between atomistic and continuum theory.

Diffusion of Brownian particles: dependence on the structure of the periodic potentials

We present here a study of the diffusive motion of a particle submerged in bistable and metastable periodic potentials within the framework of the Brownian motion theory. This is done through an investigation of the quasi-elastic peak in the dynamic structure factor S s( q, ω). Its width is found to contain valuable information on the mechanism for the diffusion process. For this study, we use the Fokker-Planck equation, which is solved numerically by the matrix-continued fraction method (MCFM) for wide system parameters' range and for the both types of potentials. It is the purpose of the present work to study how the transport properties of the system are modified by going from bistable to metastable periodic potential. Our finding results indicate large difference between transport properties in bistable and metastable potentials essentially at low temperature. In fact, in the former case, the mechanism process results from a combination of inter-cell liquid-like and intra-cells hopping motion of the particle. While for the second case, the diffusive process consists only of hopping motion, with different jump lengths, inside and between the cells. So, in metastable potential, a simple jump model describes the diffusive motion quite well. Further, a direct comparison between the numerical diffusion coefficient D and the analytical approximation for both potential shapes in the intermediate friction limit is presented and discussed.