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Possible options for modernization of the neutron beam forming system of the DN-6 diffractometer for the study of crystal and magnetic structures of microsamples at high pressures are being considered. It was demonstrated that for samples with the cross-section not exceeding 5 × 5 mm2 the most efficient option would be the use of an elliptical neutron guide. It allows to deliver neutrons for large distances from the source to samples with minimal losses using, as a rule, just one neutron reflection per dimension i.e. one at a side and one at top or bottom. For the present moment due to technical difficulties of such option realization, the simplified solution was proposed. At the end of the curved neutron guide it is planned to install a vertical plane focusing 7-meter-long parabolic section. Such a modernization will increase the neutron flux at the sample by a factor 1.5–3.5 and reduce respectively the typical measurement times.

The applicability of the modified kinematic approximation for simulation of the specular reflection and the diffraction of a neutron beam from regularly ordered nanostructured objects on the surface and in the surface material layer is analyzed. The obtained results are compared with those of the real experiment and simulation of the distorted-wave Born approximation (DWBA). The influence of various factors on the obtained results is analyzed. These factors include the effect of neutron-wave refraction at the interfaces between media, the spectrometer-resolution function, and renormalization of the results for a nonspecular scattering signal based on data obtained for a specular channel. It is shown that, in many cases, it is possible to obtain rather good agreement with the experimental data and with the results of calculations using DWBA methods and of calculations using the Parratt algorithm.

The sensitivity of the spin-echo small-angle neutron scattering technique based on magnetic fields that increase linearly with time is analyzed depending on the scattering geometry and the detector apperture. The application of sectoral collimators for the selection of scattering neutron trajectories is substantiated with the aim of improving the resolution and the corresponding effect on the data acquisition time is estimated.

The applicability of the modified kinematic approximation to describe the off-specular neutron scattering from interfaces between media is analyzed. It is demonstrated that in some cases one can expect not only a qualitative but also a quantitative agreement between the data and the results of experiments and calculations based on more accurate techniques. Diffuse scattering from rough surfaces and thin films with correlated and noncorrelated roughness of the upper and lower interfaces and the neutron diffraction by stripe magnetic domains and magnetic domains with a random size distribution (magnetic roughness) are considered as examples.

As neutron simulations packages are used for analysis of the expected performance for practically all newly built neutron instruments, possibilities for simulations with polarized neutrons have been relatively underdeveloped. During the last years we developed a new approach for the representation of time-dependent magnetic fields (both in magnitude and direction) for the VITESS simulation package. This allowed us to simulate the neutron spin dynamics in practically all polarized neutron devices (RF neutron flipper, adiabatic gradient RF flipper, the Drabkin resonator, etc.). In this article the above-mentioned VITESS instrument components (modules) will be presented and the simulated performance of a number of polarized neutron scattering instruments (NRSE, MIEZE, SESANS, etc.) will be demonstrated. Thus, we practically complete the polarized neutron suite of the VITESS, which seems sufficient for the simulation of performance of any existing polarized neutron scattering instrument. Future work will be concentrated on developments of dedicated sample modules (kernels) to allow for virtual experiments with VITESS.

We consider a new configuration for a neutron small angle scattering instrument at the pulsed IBR-2M reactor with a mixed (cold and thermal) moderator system. This system provides added-up spectra from the cold and thermal parts of the moderator. We have installed the spectrometer using a special collimation system formed by two parts: primary with neutron optics element (divergent neutron guide) and secondary (installed after the divergent neutron guide) with a multiple pinhole collimation system. Our efforts have the goal to obtain smaller Q min values (as well as higher resolution) with the possibilities to take advantage of an increased neutron flux compared with the present SANS spectrometer in the limited beam hall size. The Monte Carlo simulations will be used to choose and optimize the spectrometer and extraction system using VITESS software package.

Handling of polarization became very important in simulations of neutron scattering. One of the very comprehensive and open-source neutron simulation package, VITESS, has been intensely involved in polarized neutron simulations. Several examples will be shown here. Another similar package NISP also contains polarization tools. McStas has implemented an initial set of routines handling polarization, as our examples will also show.

The neutron spin-echo (NSE) method, that is the most powerful tool of high-resolution neutron spectroscopy, is known in two versions: with the long solenoids and short alternating fields. Here we consider an alternative version that makes use of spin flippers consisting of thin magnetic foils with an in-plane rotating magnetic field vector. MNCP simulations show the perfect performance of the NSE spectrometer build upon such flippers. Requirements to thin magnetic foils are estimated. Some possible applications of such technique are discussed. This approach can be considered as an alternative to the present-day NSE techniques.

Recent developments of the VITESS Monte Carlo software package for simulation of neutron scattering instruments allow for the computation of neutronic systems of very complex geometry. For example, the module ‘supermirror ensemble’ simulates a number of supermirror plane sections in any geometry, including spin dependent reflectivity and absorption. This module was intensively used in the optimisation of the bi-spectral extraction system for the new guide hall of BENSC at HMI. It was also used for simulations of beam splitter polarizing cavities at BENSC. Another example is the module ‘Fermi chopper’ which simulates real three-dimensional slit packages with no analytic approximations. It will also be shown that this latter module has been very successfully bench-marked with HET/ISIS experimental data and is consistent with analytic theory. Finally, we will present a sophisticated Monte Carlo simulation study of a time-focused pulsed source crystal analyzer spectrometer prototype, which is planned to be realized in a test at IPNS. A short account will be given of this example illustrating the high performance of the VITESS simulation package.

The neutron spin-echo (NSE) method, which is the most powerful tool of high-resolution neutron spectroscopy, is known in two versions: with the long solenoids and short alternating fields. Here we consider an alternative version that makes use of spin flippers consisting of thin magnetic foils (TMF) with an in-plane rotating magnetic field vector. MNCP simulations show the perfect performance of the NSE spectrometer build upon such flippers. The requirements for TMF are estimated. Some possible applications of such technique are discussed. This approach can be considered as an alternative to the present day NSE techniques.

Soller-type collimators with supermirror coating may be used for polarisation of neutron beams. The disadvantage of such devices is a high level of gamma background and fast neutrons in the case of pulsed neutron sources. In order to increase the neutron flux, the collimator was made convergent. Generally, benders make it possible to suppress the fast neutron and gamma background completely. The combination of a bender and a convergent Soller collimator (convergent or focusing bender) is proposed for polarisation of the neutron beam for future NSE spectrometers at the cold source of ESS. Simulations and optimisation of convergent benders as neutron polarisers for NSE spectrometers are presented. The VITESS software package proved to be a powerful tool for the optimisation of polarising devices.

Neutron guides are widely used to transport the neutrons from the moderator to the sample. Due to the constructive features of the ring corridor of the fast pulsed reactor IBR-2, the minimal distance between the moderator and the guide entrance is around 6 m. The main goal of the paper is to optimize the neutron optical system between the moderator and the entrance of the new neutron guides. Using Monte Carlo simulations we calculate the possible best gain of the neutron flux density at the guide exit. After the described optimization process, the optimal system is obtained. The recommendations for construction of the new beam line are provided too. Similar technique and the proposed system could be easily adapted for another similar beam line at the neutron sources.

The software package VITESS for the simulation of neutron scattering instruments is presented. The concept, the main features and the use of the program are described. The new features of version 2.5 are explained in detail. A survey of the existing modules is given. Particular emphasis is given to modules that are used to simulate optical components, such as 'supermirror ensemble', 'monochromator/analyser' or 'bender'. Examples of simulations of existing and planned instruments are presented, e.g. a powder diffractometer installed on a long pulse target station using wavelength frame multiplication. Simulation results of the existing instrument HET at ISIS are compared to experimental results. Furthermore, a view to the coming version 2.6 is presented. One of its features is discussed in detail: It will be possible to optimize parts of the instruments numerically. As a first application, focusing guides were optimized. General results of this method as well as results for a special instrument are shown. Finally, a general outlook to the planned developments of VITESS is presented.