New perspectives for neutron imaging through advanced event-mode data acquisition

Imaging using scintillators is a widespread and cost-effective approach in radiography. While different types of scintillator and sensor configurations exist, it can be stated that the detection efficiency and resolution of a scintillator-based system strongly depend on the scintillator material and its thickness. Recently developed event-driven detectors are capable of registering spots of light emitted by the scintillator after a particle interaction, allowing to reconstruct the Center-of-Mass of the interaction within the scintillator. This results in a more precise location of the event and therefore provides a pathway to overcome the scintillator thickness limitation and increase the effective spatial resolution of the system. Utilizing this principle, we present a detector capable of Time-of-Flight imaging with an adjustable field-of-view, ad-hoc binning and re-binning of data based on the requirements of the experiment including the possibility of particle discrimination via the analysis of the event shape in space and time. It is considered that this novel concept might replace regular cameras in neutron imaging detectors as it provides superior detection capabilities with the most recent results providing an increase by a factor 3 in image resolution and an increase by up to a factor of 7.5 in signal-to-noise for thermal neutron imaging.

Development of high intensity neutron source at the European Spallation Source

The European Spallation Source being constructed in Lund, Sweden will provide the user community with a neutron source of unprecedented brightness. By 2025, a suite of 15 instruments will be served by a high-brightness moderator system placed above the spallation target. The ESS infrastructure, consisting of the proton linac, the target station, and the instrument halls, allows for implementation of a second source below the spallation target. We propose to develop a second neutron source with a high-intensity moderator able to (1) deliver a larger total cold neutron flux, (2) provide high intensities at longer wavelengths in the spectral regions of Cold (4–10 Å), Very Cold (10–40 Å), and Ultra Cold (several 100 Å) neutrons, as opposed to Thermal and Cold neutrons delivered by the top moderator. Offering both unprecedented brilliance, flux, and spectral range in a single facility, this upgrade will make ESS the most versatile neutron source in the world and will further strengthen the leadership of Europe in neutron science. The new source will boost several areas of condensed matter research such as imaging and spin-echo, and will provide outstanding opportunities in fundamental physics investigations of the laws of nature at a precision unattainable anywhere else. At the heart of the proposed system is a volumetric liquid deuterium moderator. Based on proven technology, its performance will be optimized in a detailed engineering study. This moderator will be complemented by secondary sources to provide intense beams of Very- and Ultra-Cold Neutrons.

3D sub-pixel correlation length imaging

Quantitative 2D neutron dark-field-imaging with neutron grating interferometry has been used to characterize structures in the size range below the imaging resolution. We present the first 3D quantitative neutron dark-field imaging experiment. We characterize sub-pixel structure sizes below the imaging resolution in tomography by quantitatively analyzing the change in dark-field contrast with varying neutron wavelength. This proof of principle experiment uses a dedicated reference sample with four different solutions of microspheres, each with a different diameter. The result is a 3D tomogram featuring a real space scattering function in each voxel. The presented experiment is expected to mark the path for future material science research through the individual quantification of small-angle scattering structures in each voxel of a volume of a bulk inhomogeneous sample material.

Achromatic Non-Interferometric Single Grating Neutron Dark-Field Imaging

We demonstrate a simple single grating beam modulation technique, which enables the use of a highly intense neutron beam for differential phase and dark-field contrast imaging and thus spatially resolved structural correlation measurements in full analogy to interferometric methods. In contrast to these interferometric approaches our method is intrinsically achromatic and provides unprecedented flexibility in the choice of experimental parameters. In particular the method enables straight forward application of quantitative dark-field contrast imaging in time-of-flight mode at pulsed neutron sources. Utilizing merely a macroscopic absorption mask unparalleled length scales become accessible. We present results of quantitative dark-field contrast imaging combining microstructural small angle scattering analyses with real space imaging for a variety of materials.

Visualizing the heterogeneous breakdown of a fractal microstructure during compaction by neutron dark-field imaging

Structural properties of cohesive powders are dominated by their microstructural composition. Powders with a fractal microstructure show particularly interesting properties during compaction where a microstructural transition and a fractal breakdown happen before compaction and force transport. The study of this phenomenon has been challenging due to its long-range effect and the subsequent necessity to characterize these microstructural changes on a macroscopic scale. For the detailed investigation of the complex nature of powder compaction for various densification states along with the heterogeneous breakdown of the fractal microstructure we applied neutron dark-field imaging in combination with a variety of supporting techniques with various spatial resolutions, field-of-views and information depths. We used scanning electron microscopy to image the surface microstructure in a small field-of-view and X-ray tomography to image density variations in 3D with lower spatial resolution. Non-local spin-echo small-angle neutron scattering results are used to evaluate fitting models later used as input parameters for the neutron dark-field imaging data analysis. Finally, neutron dark-field imaging results in combination with supporting measurements using scanning electron microscopy, X-ray tomography and spin-echo small angle scattering allowed us to comprehensively study the heterogeneous transition from a fractal to a homogeneous microstructure of a cohesive powder in a quantitative manner.

A Monte Carlo approach for scattering correction towards quantitative neutron imaging of polycrystals

The development of neutron imaging from a qualitative inspection tool towards a quantitative technique in materials science has increased the requirements for accuracy significantly. Quantifying the thickness or the density of polycrystalline samples with high accuracy using neutron imaging has two main problems: (i) the scattering from the sample creates artefacts on the image and (ii) there is a lack of specific reference attenuation coefficients. This work presents experimental and simulation results to explain and approach these problems. Firstly, a series of neutron radiography and tomography experiments of iron, copper and vanadium are performed and serve as a reference. These materials were selected because they attenuate neutrons mainly through coherent (Fe and Cu) and incoherent (V) scattering. Secondly, an ad hoc Monte Carlo model was developed, based on beamline, sample and detector parameters, in order to simulate experiments, understand the physics involved and interpret the experimental data. The model, developed in the McStas framework, uses a priori information about the sample geometry and crystalline structure, as well as beamline settings, such as spectrum, geometry and detector type. The validity of the simulations is then verified with experimental results for the two problems that motivated this work: (i) the scattering distribution in transmission imaging and (ii) the calculated attenuation coefficients.

Unlocking high spatial resolution in neutron imaging through an add-on fibre optics taper

The demand for high resolution neutron imaging has been steadily increasing over the past years. The number of facilities offering cutting edge resolution is however limited, due to (i) the design complexity of an optimized device able to reach a resolution in the order of ≈ 10 μm and (ii) limitations in available neutron flux. Here we propose a simple addition, based on a Fibre Optics Taper (FOT), that can be easily attached to an already existing scintillator-camera imaging detector in order to efficiently increase its spatial resolution and hence boost the capability of an instrument into high resolution applications.

Statistical uncertainty in the dark-field and transmission signal of grating interferometry

We present a framework to estimate the fundamental statistical uncertainty of grating interferometer experiments based on a Monte-Carlo method. Using the framework, we are able to determine the uncertainty of individual measurements as well as suggesting experimental protocols that minimise the statistical uncertainty for given overall exposure times. The method presented here is valid for both X-rays and neutrons and can be generalised for any modulation measurement.

BioRef II-Neutron reflectometry with relaxed resolution for fast, kinetic measurements at HZB

We present an upgrade to the time-of-flight neutron reflectometer BioRef at the research reactor BER II of the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB). Through the integration of an additional chopper into the existing setup, the available wavelength resolution is significantly extended. Now two distinct operation modes can be used: a high resolution mode with Δλ/λ ranging from 1% to 5%, which allows for the investigation of thick films up to 4000 Å, and a high flux mode with Δλ/λ = 7%-11%. In the high flux mode, reflectivity curves from 0.007 Å^-1 to 0.2 Å^-1 with three angular settings can be recorded in 7 min. For a single angular setting and its respective window in Q-space, a time resolution of even less than 4 min is reached. The different configurations are documented by respective measurements (a) on a Ni-Ti multilayer and (b) the swelling kinetics of a solid-supported phospholipid coating upon incubation in a polyelectrolyte solution.

Wavelength-dispersive dark-field contrast: micrometre structure resolution in neutron imaging with gratings

Dark-field imaging using grating interferometers has been proven to have a high potential for applications in engineering, magnetism, and soft matter and biophysics, as well as in medicine with both neutrons and X-rays. The access to spatially resolved small-angle scattering information in neutron dark-field imaging provides information about structures beyond direct spatial image resolution. The dark-field contrast modality is hence a valuable tool for materials science based on neutron imaging. This is underlined by the success of the method, despite its current limitation to qualitative scattering information. Here it is demonstrated how a wavelength-dispersive approach allows such drawbacks to be overcome by providing quantitative structure size information and hence can introduce novel possibilities and insights for materials science.

Quantification of the sensitivity range in neutron dark-field imaging

In neutron grating interferometry, the dark-field image visualizes the scattering properties of samples in the small-angle and ultra-small-angle scattering range. These angles correspond to correlation lengths from several hundred nanometers up to several tens of micrometers. In this article, we present an experimental study that demonstrates the potential of quantitative neutron dark-field imaging. The dark-field signal for scattering from different particle sizes and concentrations of mono-dispersive polystyrene particles in aqueous solution is compared to theoretical predictions and the good agreement between measurements and calculations underlines the quantitative nature of the measured values and reliability of the technique with neutrons.

Neutron guide optimisation for a time-of-flight neutron imaging instrument at the European Spallation Source

A neutron transport system for the planned imaging instrument ODIN at the future European Spallation Source (ESS) based on neutron optical components was designed and optimized. Different ways of prompt pulse suppression were studied. The spectral performance of the optimal neutron guide configuration is presented. In addition, the influence of the gaps in the guide system needed for the required chopper configuration was investigated. Given that the requirements for an imaging instrument located on a long guide system and hosting a complex chopper system are extremely demanding in terms of spectral and divergence needs, this study can be beneficial for a wide range of instruments in various ways.

The contribution of glutathione to the destabilizing effect of yeast on wheat dough

Any factor which impairs the development of the gluten network affects the gas retention capacity and the overall baking performance. This study aimed to examine why rising yeast concentrations (Saccharomyces cerevisiae) decrease the dough elasticity in an asymptotic manner. Since in 27 commercial fresh and dry yeasts up to 81 mg glutathione (GSH) per 1g dry sample were found. Through the addition of reduced GSH in dough without yeast, the extent of dough weakening was analysed. Indeed rheological measurements confirmed that yeast-equivalent levels of GSH had a softening effect and during 3h fermentation the weakening coefficient increased from 0.3% to 20.4% in a Rheofermentometer. The present results indicate that free -SH compounds, as represented by GSH, considerably contribute to the softening of dough through dead yeast cells.

BioRef: a versatile time-of-flight reflectometer for soft matter applications at Helmholtz-Zentrum Berlin

BioRef is a versatile novel time-of-flight reflectometer featuring a sample environment for in situ infrared spectroscopy at the reactor neutron source BER II of the Helmholtz Zentrum Berlin für Materialien und Energie (HZB). After two years of design and construction phase the instrument has recently undergone commissioning and is now available for specular and off-specular neutron reflectivity measurements. BioRef is especially dedicated to the investigation of soft matter systems and studies at the solid-liquid interface. Due to flexible resolution modes and variable addressable wavelength bands that allow for focusing onto a selected scattering vector range, BioRef enables a broad range of surface and interface investigations and even kinetic studies with subsecond time resolution. The instrumental settings can be tailored to the specific requirements of a wide range of applications. The performance is demonstrated by several reference measurements, and the unique option of in situ on-board infrared spectroscopy is illustrated by the example of a phase transition study in a lipid multilayer film.

Neutron dark-field tomography

We report how a grating interferometer yields neutron dark-field scatter images for tomographic investigations. The image contrast is based on ultrasmall-angle scattering. It provides otherwise inaccessible spatially resolved information about the distribution of micrometer and submicrometer sized structural formations. Three complementary sets of tomographic data corresponding to attenuation, differential phase, and small-angle scattering can be obtained from one measurement. The method is compatible with conventional imaging and provides significantly higher efficiency than existing techniques.

[Obstructive jaundice and acute pancreatitis due to an obstruction of the afferent loop after billroth-II-resection]

An obstruction of the afferent loop after Billroth-II-resection is an extremely rare late complication of this procedure. We report on a 76-year-old female patient with a history of Billroth-II-resection 11 years ago who was admitted due to acute pancreatitis and obstructive jaundice. Abdominal sonography lead to the suspicion of a dilated afferent loop, which could be proven by means of magnetic resonance imaging. A tumorous lesion as cause of the obstructive jaundice was not detectable. Intraoperatively a volvulus of the small intestine and strangling adhesions near the Braun's anastomosis were seen, causing the obstruction of the afferent loop. Following reposition of the small intestine and adhesiolysis the patient gained a quick relief of symptoms and the jaundice disappeared completely.

Synthesis of pentasaccharide core structures corresponding to the genus-specific lipopolysaccharide epitope of Chlamydia

The trisaccharides allyl O-(sodium 3-deoxy-alpha-D-manno-2-octulopyranosylonate)-(2-->6)-O-2-aceta mid o-2-deoxy- beta-D-glucopyranosyl-(1-->6)-2-acetamido-2-deoxy-alpha- and -beta-D-glucopyranoside (16a and 16b), the tetrasaccharides allyl O-(sodium 3-deoxy-alpha-D-manno-2-octulopyranosylonate)-(2-->4)-O-(sodium 3-deoxy-alpha-D-manno-2-octulopyranosylonate)-(2-->6)-O-2-aceta mid o-2-deoxy- beta-D-glucopyranosyl-(1-->6)-2-acetamido-2-deoxy-alpha- and -beta-D-glucopyranoside (19a and 19b), and the pentasaccharides allyl O-(sodium 3-deoxy-alpha-D-manno-2-octulopyranosylonate)-(2-->8)-O-(sodium 3-deoxy-alpha-D-manno-2-octulopyranosylonate)-(2-->4)-O-(sodium 3-deoxy-alpha-D-manno-2-octulopyranosylonate)-(2-->6)-O-2-aceta mid o-2-deoxy-bet a -D-glucopyranosyl-(1-->6)-2-acetamido-2-deoxy-alpha- and -beta-D-glucopyranoside (23a and 23b) were prepared. The glycosidic linkages were formed using 1,3,4,6-tetra-O-acetyl-2-chloroacetamido-2-deoxy-beta-D-glucopy ran ose (6) and FeCl3 as promoter as well as per-O-acetylated Kdo mono- and di-saccharide bromide derivatives (12 and 20) under Helferich conditions. The oligosaccharides, which correspond to dephosphorylated part-structures of enterobacterial and chlamydial lipopolysaccharides, were characterized by NMR spectroscopy as well as plasma desorption and matrix-assisted laser desorption mass spectrometry.

Synthesis of allyl O-[sodium(alpha-D-glycero-D-talo-2- octulopyranosyl)onate]-(2-->6)-2-acetamido-2-deoxy-beta-D-glucopyranosi de, a core constituent of the lipopolysaccharide from Acinetobacter calcoaceticus NCTC 10305

Reaction of methyl 2,6-anhydro-2,3-dideoxy-D-manno-2-octenoate 1 with 3-chloroperoxybenzoic acid gave the 2,3-anhydro derivative 2, which was converted into the per-O-acetylated anomeric methyl glycosides of D-glycero-D-galacto-2-octulopyranosylonic acid in good yield. Subsequent inversion of the configuration at C-3 and deprotection afforded sodium (methyl beta-D-glycero-D-talo-2-octulopyranosid)onate. Alternatively, 2 was transformed into methyl (alpha-D-glycero-D-talo-2- octulopyranosyl bromide(onate derivatives. Reaction with methanol or allyl 2-acetamido-2-deoxy- 3,4-O-(1,1,3,3-tetraisopropyldisiloxan-1,3-diyl)-beta-D-g lycopyranoside, promoted by silver triflate, gave good yields of the corresponding orthoester derivatives. Me3Si triflate-catalyzed orthoester rearrangement and removal of the protecting groups afforded sodium O-(methyl alpha-D-glycero- D-talo-2-octulopyranosid)onate and the disacchanide, allyl O-[sodium(alpha-D-glycero-D-talo-2- octulopyranosyl)onate]-(2-->6)-2-acetamido-2-deoxy-beta-D-gl ucopyranoside in high yield.

[Individual face masks as aids in quasi-3-D planning and completion of irradiation of tumors of the head and neck]

Apparatus for immobilizing the patient's head in an identically reproducible position is required, if the advantages of exact quasi-3-D-therapy planning are to be fully exploited for the irradiation of irregular target volumes in the head and neck area. The topics of this report are the production and application of individual thermoplastic masks in connection with special head supports for CT planning scans, simulation and irradiation.