J. Dawidowski

On the analysis of deep inelastic neutron scattering experiments for light nuclei

We analyze different procedures for data processing in deep inelastic neutron scattering experiments focussing our attention on experiments performed on light nuclei. We first examine experiments in which the desired information is obtained from the observed peak areas in the particular case of mixtures of light and heavy water. In the second part we examine the procedure to obtain an effective temperature from the experimental peaks. As a consequence of the results emerging from both cases we trace the limits of validity of the convolution formalism usually employed, and propose a different treatment of the experimental data for this kind of measurements.

Multiple scattering and attenuation corrections in Deep Inelastic Neutron Scattering experiments

Multiple scattering and attenuation corrections in Deep Inelastic Neutron Scattering experiments are analyzed. The theoretical basis of the method is stated, and a Monte Carlo procedure to perform the calculation is presented. The results are compared with experimental data. The importance of the accuracy in the description of the experimental parameters is tested, and the implications of the present results on the data analysis procedures is examined.

Enhanced plastic neutron shielding for thermal and epithermal neutrons

We describe a compound made of paraffin and boron carbide (boraffin) deviced to enhance epithermal neutron shielding. The compound is easily prepared and is specially suited to be adapted to particular surfaces. Transmission experiments show a favourable comparison with a commercial rubber-boron carbide compound in the epithermal range. A detector shielding built with this material is described and the achieved background reduction experimentally determined is shown.

Analysis of multiple scattering and multiphonon contributions in inelastic neutron scattering experiments

Abstract We present a method of analysis of inelastic neutron scattering (INS) experiments aiming at obtaining the density of phonon states in an absolute scale, as well as a reliable value of the mean-square displacement of the atoms. This method requires the measurement of the neutron total cross section of the sample as a function of energy, which provides a normalization condition for the INS experiment, as well as a value of the mean-square displacement. The method is applied in the case of an incoherent neutron scattering system, viz. the Ti–52wt.% Zr alloy. The applicability of this method to the study of metal alloys and other systems is discussed.

Multiple scattering and inelasticity distortions in neutron scattering from an infinite plane slab

Abstract Multiple scattering and inelasticity effects in neutron scattering by a gaseous sample with an infinite plane slab geometry is studied as a function of the scattering angle for a perpendicular monochromatic incident beam. The importance of inelasticity effects in the treatment of the multiple scattering problem is shown. Monte Carlo simulations as well as approximate calculations are presented, and a correction procedure is proposed for the situation considered.

Performance of the second Deep Inelastic Neutron Scatering spectrometer at the Bariloche electron LINAC

We report on the new Deep Inelastic Neutron Scattering detector bank recently implemented at the Bariloche electron LINAC. We show the characterization and calibration process carried out, which comprises the determinarion of the detector bank efficiency, and the evaluation of the performance of the filter difference technique. As part of the benchmarking process, polyethylene spectra were measured and analyzed, and the scattering cross sections for carbon and hydrogen were determined in the process. With the addition of this new detector bank to the existing one, we evaluate the combined capacity of the two banks.

Data Processing Steps in Neutron Diffraction: From the Raw Data to the Differential Cross Section

Neutron diffraction is a well established tool to investigate the structure of matter in a wide range of disciplines including Physics, Chemistry, Materials Sciences, Life Sciences, Earth Sciences and Engineering. One of its most required applications is the refinement of structures for which a considerable instrumental development has been devoted. In particular, the improvement of the instrumental resolution has been hitherto one of the main concerns in the development of the technique. In other words, most of the efforts in the instrumental development and methods has been devoted to improve the abscissas of the experimental scale (angle or momentum transfer), while on the other hand, the final results in ordinates are normally left in arbitrary units, since most of the applications do not require an absolute normalization.

Structure factor determination of deuterated 1- and 2-propanol using diffraction experiments with polarization analysis

We present the experimental structure factors of deuterated 1- and 2-propanol as determined at the Spin Polarized Hot Neutron Beam Facility (D3) of the Institut Laue Langevin. Polarized neutron scattering with polarization analysis has the advantage of experimentally separating the coherent and incoherent scattering intensities. Using a linear combination of non-spin-flip and spin-flip diffractograms, one can determine the coherent intensity, related to the structure factor. The corrections of experimental data for multiple scattering, attenuation and inelasticity are carried out using a Monte Carlo (MC) simulation code developed for this kind of experiments. This (hybrid) MC method is based on the combination of a modelled energy exchange and the experimental angular distribution. The good agreement observed between our simulations and the experimental results, confirms the goodness of this model. We also compare our results with experimental data from other authors and we stress the need of more experimental data in the low- region.

A Monte Carlo simulation code applied to diffraction experiments with polarization analysis

Neutron diffraction with polarization analysis is a very useful technique to separate the coherent and incoherent contributions to the scattering cross section. This experimental technique allows the direct measurement of the spin-flip and non spin-flip contributions, which in turn are related to the coherent and incoherent contributions by simple linear combinations. Nevertheless, the correction procedures to obtain the single coherent elastic scattering are tricky. We present a method, based on Monte Carlo simulation, that allows one performing these corrections in a wide variety of coherent and incoherent samples. In this work, we have applied this method to the study of heavy water, for which we obtained the interference structure factor. We describe the experimental setup to perform the measurements in a reactor source and we detail the experimental protocol allowing the determination of the non spin-flip and spin-flip diffractograms.

Proposal for instruments at small and medium size neutron facilities

The deployment of small and medium intensity regional neutron sources facilitates the availability of neutron techniques to a wider users community. With a minimum set of instruments it is possible to cover a variety of applications. Based on the experience gained with the use of the Bariloche Electron Linear Accelerator (Argentina), we propose a few basic instruments that are suitable to be installed at a small or medium scale neutron facility.