Excitation of levels by inelastic neutron scattering

A scintillation spectrometer in ring geometry was used to study the gamma rays accompanying the inelastic scattering of fast neutrons on Na, Mg, Mn, Fe and I. The energies of the gamma rays were in most cases arranged into the cascade decay schemes of excited nuclei. Some of the transitions, which had not yet been described, were also found. These are the lines (2147±21) keV for Mg²⁵, (2135±22) keV, (2750±40) keV, (3040±50) keV and (3200±50) keV for Mn⁵⁵ and a series of other gamma rays emitted during the interaction of fast neutrons with I¹²⁷, which are given in the paper.

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-, Na, Mg, Mn, Fe I. - . , , . (2147±21) keV y Mg²⁵, (2135±22) keV, (2750±40) keV, (3040±50) keV (3200±50) keV y Mn⁵⁵ -, c I¹²⁷, .

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In conclusion the authors thank Z. Janout for contributing to the experimental work, J. Vrzal for the design of some of the apparatus, and F. trba, lecturer at the Faculty of Technical and Nuclear Physics, for help during the measurements. Thanks go to members of the accelerator laboratory staff of the Institute of Nuclear Research J. SchÄferling, J. Filípek and particularly J. Jirou, and to J. Zikmund from the same institute for valuable advice and help in the chemical problems connected with the measurements.     

Crystal fields and pressure dependence of spin dynamics in CeAg measured by inelastic neutron scattering

We have studied polycrystalline CeAg and LaAg by inelastic neutron scattering at various temperatures betweenT=2 and 300 K and at different hydrostatic pressures up to 2.3GPa (23kbar). We point out the difficulties in the interpretation of the magnetic part of the measured spectra of CeAg at zero pressure and compare our results and interpretation with previous neutron scattering experiments. Applying pressure we find a broadening of the magnetic quasielastic line, i.e. the Ce³⁺ ion becomes more unstable. We observe still a strong temperature dependence, which means there is no indication of a classical intermediate-valent behaviour of the Ce ions up to 2.3 GPa.     

Crystal field splitting of Pr3+ in PrAl2 investigated by inelastic neutron scattering

We report the.results of an experimental determination of the crystal field splitting of Pr³⁺ in PrAl₂ by means of inelastic neutron scattering. For the crystal field parameters we obtain B₄ = (47.2 ± 4.0) × 10^?4 meV and B₆ = ? (156 ± 12) × 10^?6 meV.     

Phonon eigenvectors in Si determined by inelastic neutron scattering

We have determined the eigenvectors of longitudinal phonons with wavevectors in the direction in Si at 12 K from inelastic neutron scattering intensities. The eigenvectors obtained from different model and quantum-mechanical calculations are at variance. Comparison of experimental and theoretical results shows that of the various theoretical predictions the ones from the bond-charge model are in best agreement with experiment. Internal-strain constants from these models and from experiment are compared.     

The determination of crystal field levels in the intermetallic compound HoRh by inelastic neutron scattering

Inelastic neutron time of flight measurements have been carried out on the intermetallic compound HoRh at different temperatures. Well resolved transitions between crystal field levels were observed at 4.0 and 9.7 meV. The complete crystal field level scheme was deduced and the crystal field parameters were found to be A₄⁰ 〈r⁴〉 = ?10.98 meV and A₆⁰ 〈r⁶〉 = ?1.59 meV. These values deviate considerably from point charge estimates.     

Cross section of inelastic polarized neutron scattering by superconducting rings

A general expression for the cross section of inelastic magnetic scattering of cold polarized neutrons by superconducting rings has been derived. In this scattering process, the metastable superconducting current changes via quantum jumps corresponding to a decrease in the number of fluxoids in the superconducting ring by one or several units and the change in the energy of the ring is transferred to the kinetic energy of the scattered neutron. For rings from type-II superconductors with a thickness smaller than the field penetration depth but larger than the electron mean free path, the cross sections of inelastic scattering with neutron spin flip have been obtained for the first time. The possibility of increasing the cross section of neutron scattering by a system of rings has been discussed.     

Lattice dynamics of cubic PbTiO3 by inelastic neutron scattering

High-temperature dispersion relations of the phonon modes in a cubic PbTiO₃ single crystal have been investigated along the [ξ 0 0] and [ξ ξ 0] directions by inelastic neutron scattering. Above T _c, the phonon dispersions are only temperature-dependent close to the Brillouin zone centre where the mode softening comes through. The measurements indicate large cubic anisotropy of the elastic tensor and relatively low anisotropy of the soft mode dispersion. The differences from an earlier inelastic neutron scattering study are discussed.     

Collective dynamics of lipid membranes studied by inelastic neutron scattering

We have studied the collective short wavelength dynamics in deuterated 1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine (DMPC) bilayers by inelastic neutron scattering. The corresponding dispersion relation variant Planck's over 2pi omega(Q) is presented for the gel and the fluid phase of this model system. The temperature dependence of the inelastic excitations indicates a phase coexistence between the two phases over a broad range and leads to a different assignment of excitations from that reported in a preceding inelastic x-ray scattering study [Phys. Rev. Lett. 86, 740 (2001)]]. As a consequence, we find that the minimum in the dispersion relation is actually deeper in the gel than in the fluid phase. Finally, we can clearly identify an additional nondispersive (optical) mode predicted by molecular dynamics simulations [Phys. Rev. Lett. 87, 238101 (2001)]].     

Elastic constants in RbI,determined by inelastic neutron scattering

Long-wavelength acoustic phonons have been studied in the whole (100)-plane of RbI at 295 K by means of inelastic neutron scattering. The raw data have been corrected for resolution effects taking into account the curvature of the dispersion surface and variations of the mode eigenvectors. The shifts of the neutron groups due to these resolution effects are discussed in detail. The analysis of the experimental results gives for the zero sound elastic constantsc ₁₁=28.15±0.5,c ₁₂=3.7±0.5 andc ₄₄=2.85±0.1 10¹⁰ dyn/cm². A comparison with first sound elastic constants taken from ultrasonic measurements yields significant differences between the high and low frequency elastic constantsc ₁₁ andc=(c ₁₁–c ₁₂)/2. The differences calculated from recent theories are in agreement with the experimental results for the elastic constantsc ₁₁,c ₄₄ andc, but not forc ₁₂. The dispersion surface in the (100)-plane is also shown for some out-of-symmetry data and compared with ultrasonic data as well as with theoretical results.Research supported by BMFT     

Hydrodynamic effects in bicontinuous microemulsions measured by inelastic neutron scattering

The dynamical properties of bicontinuous microemulsions have been studied with neutron spin echo spectroscopy around length scales corresponding to the correlation peak q₀. Comparison of samples with different contrasts for neutrons shed light on the two modes dominated either by variation of the oil/water difference or surfactant concentration in the hydrodynamic regime. The results have been compared to theoretical predictions of the relaxation rates of bicontinuous microemulsions by Nonomura and Ohta [M. Nonomura, T. Ohta, J. Chem. Phys. 110, 7516 (1999)]. The influence of modification of the surfactant layer bending constants in the microemulsion by addition of homopolymers (polyethylenepropylene: PEP_X and polyethyleneoxide: PEO_X, X=5 kg/mol), dissolved in the oil phase and water, has been investigated.     

The spectroscopy of 13C by inelastic proton scattering

At 135 MeV incident energy, differential proton scattering cross sections have been measured for many states of ¹³C, up to 23 MeV in excitation. These data are supplemented by analysing power data for states up to 10 MeV in excitation, measured at 119 MeV incident energy. Distorted wave analysis using a density-dependent form of the nucleon-nucleon interaction has provided a thorough assessment of the model predictions of the nuclear structure of many of these excited states.     

Study of hydrogen chemisorbed on Raney-nickel by neutron inelastic spectroscopy

The motion of chemisorbed hydrogen on the Raney-nickel surface was studied by neutron inelastic spectroscopy. The peaks found at low energy transfers (below 320 cm^?1) are nearly identical to the spectrum of lattice frequencies of pure nickel. This means that each hydrogen atom is bound to only one nickel atom. The mean square amplitude of the bound proton was found to exceed that of nickel by 0.04 ± 0.02 Ų. A broad band found at 1120 cm^?1 (800 cm^?1 in the case of deuterium) is attributed to motions of hydrogen atoms relative to the nickel surface. An interpretation of this band is given in terms of harmonic approximation. An analysis of the shape of the elastic line has shown that no broadening could be detected with our instrument. This leads to an upper limit for the diffusion constant of the protons, D<5×10^?7 cm²/s, at room temperature.     

Zero- and first-sound damping in NaF observed by inelastic neutron scattering

The frequency and temperature dependence of the damping of transverse acoustic modes with 0.06 ? q/q_max ? 0.25 in NaF was determined by means of inelastic neutron scattering. The results clearly show a transition from the Akhiezer to the Landau-Rumer regime.     

Dynamics of supercooled confined water measured by deep inelastic neutron scattering

In this paper, we present the results of deep inelastic neutron scattering (DINS) measurements on supercooled water confined within the pores (average pore diameter ~ 20 Å) of a disordered hydrophilic silica matrix obtained through hydrolysis and polycondensation of the alkoxide precursor Tetra-Methyl-Ortho-Silicate via the sol-gel method. Experiments were performed at two temperatures (250 K and 210 K, i.e., before and after the putative liquid–liquid transition of supercooled confined water) on a “wet” sample with hydration h ~ 40% w/w, which is high enough to have water-filled pores but low enough to avoid water crystallization. A virtually “dry” sample at h ~ 7% was also investigated to measure the contribution of the silica matrix to the neutron scattering signal. As is well known, DINS measurements allow the determination of the mean kinetic energy and the momentum distribution of the hydrogen atoms in the system and therefore, allow researchers to probe the local structure of supercooled confined water. The main result obtained is that at 210 K the hydrogen mean kinetic energy is equal or even slightly higher than at 250 K. This is at odds with the predictions of a semiempirical harmonic model recently proposed to describe the temperature dependence of the kinetic energy of hydrogen in water. This is a new and very interesting result, which suggests that at 210 K, the water hydrogens experience a stiffer intermolecular potential than at 250 K. This is in agreement with the liquid–liquid transition hypothesis.     

Probing hole-induced ferromagnetic exchange in magnetic semiconductors by inelastic neutron scattering

The effect of hole doping on the exchange coupling of the nearest neighbor (NN) Mn pairs in Zn(1-x)MnxTe is probed by inelastic neutron scattering. The difference in the NN exchange energy DeltaJ1 in the presence and in the absence of the holes is determined. The obtained value of DeltaJ1 is in good agreement with the predictions of the Zener/RKKY model, even on the insulator side of the metal-insulator transition.