Journal of Neutron Research - Volume 11, issue 3

Authors: Weber, J.K.R. | Benmore, C.J. | Tangeman, J.A. | Siewenie, J. | Hiera, K.J.

Article Type: Research Article

Abstract: The total structure factors, S(Q) of 50:50 mole% CaO:Al2 O3 - and 67:33 mole% SrO:Al2 O3 -composition liquids have been determined by neutron diffraction. Measurements were made on laser beam-heated liquids at 2000–2100 K held in an aerodynamic levitator. Pure vanadium levitation nozzles were used. Reduction of the nozzle wall thickness decreased attenuation of scattered neutrons to give a two-fold increase in signal intensity. The liquids are comprised of predominantly 4-coordinated aluminum and 6- and higher-coordinated group II metal ions.

Keywords: Liquid structure, levitation, containerless, neutron diffraction, aluminates

DOI: 10.1080/1023816031000099746

Citation: Journal of Neutron Research, vol. 11, no. 3, pp. 113-121, 2003

Authors: Colognesi, D. | Andreani, C. | Degiorgi, E.

Article Type: Research Article

Abstract: We have studied two “ice-like” systems, H2 S and HCl, which, despite their molecular simplicity, exhibit a rich polymorphism in solid phase. We performed incoherent neutron scattering measurements employing a new crystal-analyzer inverse-geometry neutron spectrometer, TOSCA-I. After a detailed data reduction procedure, we devised a technique aiming to estimate and remove the multi-phonon part of the spectra. Finally, the H-projected phonon densities of states, ZH (ω), were extracted and the respective H mean squared displacements, 〈u2 〉H , determined. These ZH (ω) show good statistical accuracy and resolution and represent an important benchmark for future lattice-dynamics simulations and phonon dispersion …curve measurements. Since some thermal softening of the phonon modes was visible in both H2 S and HCl, we tried to quantify this anharmonic effect through the zero-point proton mean squared displacement, 〈u2 inter 〉H,0 , and the zero-point proton mean kinetic energy, 〈Ek,inter 〉H,0 . Finally, approximate Grüneisen parameters for 〈u2 inter 〉H,0 and 〈Ek,inter 〉H,0 were calculated exploiting D2 S neutron diffraction data. Show more

Keywords: Hydrogen bonded solids, phonon density of states, incoherent inelastic neutron scattering, crystal-analyzer inverse-geometry spectrometer, hydrogen sulfide, hydrogen chloride

DOI: 10.1080/1023816031000140695

Citation: Journal of Neutron Research, vol. 11, no. 3, pp. 123-143, 2003

Authors: Ahmad, W. | Ahmad, M. | Rajput, M.U.

Article Type: Research Article

Abstract: The prompt gamma neutron activation analysis (PGNAA) facility at the Pakistan Research Reactor (PARR-I) has been used for elemental analysis of different kinds of materials. A high-efficiency, high-resolution gamma spectrometer based on a high-purity germanium detector is being employed in this study. The cadmium ratio of the incident neutron beam is 62 and the thermal neutron flux at the target position is about 1.5×106 n/cm2 /s. The system is usually operated in Compton suppression mode to enhance peak to background ratio in the lower energy region (<1.5 MeV). The gamma ray detector is calibrated with standard radioactive sources up …to 1.5 MeV. The aim of the present study is to determine the quantity of boron in reactor grade steels as well as in some other materials containing boron. The results of boron assessment in SS-304L and amorphous (Fe0.99 Mo0.01 )78 Si9 B13 alloy are also presented. Show more

Keywords: PGNAA, gamma spectroscopy, HPGe detectors, elemental analysis, boron, steel

DOI: 10.1080/10238160310001657808

Citation: Journal of Neutron Research, vol. 11, no. 3, pp. 145-152, 2003

Authors: Kameda, Y. | Sasaki, M. | Usuki, T. | Otomo, T. | Itoh, K. | Suzuya, K. | Fukunaga, T.

Article Type: Research Article

Abstract: Time-of-flight (TOF) neutron scattering measurements have been carried out for liquid null-H2 O, in which the average coherent scattering length of hydrogen atoms is zero. In order to determine the inelasticity effect depending on both the scattering angle and the neutron flight path ratio, γ[=ls /(l0 +ls ), l0 and ls denote the moderator-sample and sample-detector distances, respectively], neutron scattering measurements have been performed using three neutron spectrometers, HIT-II, RAT, and SWAN, installed at KENS, Tsukuba, Japan. The self-scattering intensity for the null-H2 O was derived by subtracting the known O–O partial structure factor from the observed scattering …cross-section. It has been revealed that the magnitude of the inelasticity distortion involved in the self-scattering term is still significant even at a smaller scattering angle than that expected from the first-order inelasticity correction formulas proposed in the literature. The inelasticity distortion in the self-scattering term is found to be preferably reduced by applying the small flight path ratio. An empirical but useful correction procedure for the inelasticity effect is developed using the self-scattering intensities observed for the null-H2 O. The present correction procedure is applied to the scattering cross-section observed for aqueous 3 mol% alanine solution which involves 20% H of exchangeable hydrogen atoms, and to the first-order difference function ΔH (Q) observed for 4 mol% lithium benzoate heavy water solutions in which H/D isotopic substitution has been applied for benzyl-hydrogen atoms within the benzoate ion. The results indicate that the present inelasticity correction procedure works satisfactorily for the scattering intensity from the aqueous solution containing H atoms. Show more

Keywords: Neutron diffraction, inelasticity effect, null-H2O, self-scattering, cross-section

DOI: 10.1080/10238160310001657817

Citation: Journal of Neutron Research, vol. 11, no. 3, pp. 153-163, 2003

Authors: Venturi, G. | Guarini, E. | Formisano, F. | Orecchini, A. | Cunsolo, A. | Petrillo, C. | Sacchetti, F. | Barocchi, F.

Article Type: Research Article

Abstract: Here we report on new results obtained by ad hoc developed McStas simulations of the time-of-flight thermal neutron Brillouin spectrometer BRISP, presently under construction at the ILL. In such a spectrometer a double-curvature focusing monochromator is combined with a multi-beam converging collimator. This configuration, first exploited for BRISP, has been carefully analyzed by developing new specific McStas codes which enable a reliable simulation of the real components, including the detailed features of the monochromator, the background disk-chopper and the honeycomb converging collimator. The present McStas calculations are also used as a guide to refine technical details, such as the optimal …arrangement of the crystals on the monochromator surface as a function of the measured mosaic spread. The simulation results are consistent with the expected estimates of both intensity and resolution, and show that BRISP can provide new opportunities for advanced investigations of the low-Q dynamics of disordered and magnetic systems. Show more

Keywords: Neutron scattering, instrumentation, Monte Carlo simulations, time-of-flight, small-angle spectrometer, McStas

DOI: 10.1080/1023816042000202199

Citation: Journal of Neutron Research, vol. 11, no. 3, pp. 165-178, 2003