Neutron Diffraction Facility Research Articles

Experimental cross section of the 164Dy(n,γ)165Dy reaction at the neutron energy of 0.0372 eV using Neutron Diffraction Facility

Abstract The neutron capture cross section for the 164Dy(n,γ)165Dy reaction at 0.0372 eV energy was measured using the horizontal channel (Neutron Diffraction Facility) of Es-Salam nuclear research reactor in Birine-Algeria. The Neutron Activation Analysis (NAA) technique using 197Au(n,γ)198Au as reference reaction was adopted. The γ ray spectra for the Dy2O3 target powder and two thin gold foil were detected for the Germanium Hyper Pure coupled in the Genie 2000 data acquisition software. A resulting σ-value (2198.5 ± 94) b was measured for the thermal neutron cross section after correcting the thermal neutron self-shielding and γ attenuation effects. The measured value was then compared to the evaluated cross sections reported in two different libraries of neutron databases ENDF/B-VIII.0 and JEFF-3.3. The measured data at 0.0372 eV has been extrapolated to the energy of 0.0253 eV assuming 1/ν dependence in the thermal energy region and the result was compared with the fully measured values reported in the literature.

The design and optimization of a radiation shield for the Tehran Research Reactor's neutron diffraction facility

In this paper, a novel optimal radiation shield for the Tehran research reactor's neutron powder diffraction facility was designed to reduce undesirable neutron and gamma dose rates. A layer-by-layer methodology was considered based on the design approach to achieve a dose rate of less than 30 μSv/hr. MCNPX was used for this purpose as a Monte Carlo radiation transport code. A combination of neutron and gamma absorbers and moderators was employed to create this shield. The results indicated that the shield's six distinct layers met the design objective, totaling 65 cm in thickness. This newly designed shield comprises 15 cm paraffin, 15 cm Portland iron concrete, another 15 cm paraffin, 5 cm solid boric acid, another 10 cm Portland iron concrete, and 10 cm lead. The neutron and photon dose rates are 9.35 and 12.81 μSv/hr, respectively, which is one-sixteenth and one-third of the current facility shield. Validation of the simulation was accomplished by comparing the results for the current shield to experimental data.

Modeling of the Kinetics of Strain‐Induced Martensite Transformation and the Transformation‐Induced Plasticity Effect in a Lean‐Alloyed Metastable Austenitic Stainless Steel

This article investigates the influence of temperature and strain on second‐phase transformation strengthening and the resulting mechanical properties in a lean AISI 301LN austenitic stainless steel within a temperature range of −60 to 180 °C. The volume fraction of martensite evolved is determined using nondestructive magnetic Ferritescope measurements that are adjusted by using a calibration factor of 1.7, which is established using the saturation magnetization measurements, X‐ray, and neutron diffraction measurements. The kinetics of strain‐induced martensite transformation (SIMT) as a function of strain and temperature is accurately described by a set of modified constitutive Boltzmann sigmoidal equations at temperatures below 75 °C. For this steel, the Md (30/50) temperature is determined as 61 °C. The absolute Md temperature is established as ≈109 °C, and no athermal transformation to martensite is observed upon cooling to −270 °C using cryogenic neutron diffraction facilities. Extended JMAK analysis of the transformation is used to shed light on the mechanism of martensitic transformation. It is found that the transformation‐induced plasticity (TRIP) effect due to SIMT is at a maximum at 75 °C, which is the maximum elongation temperature (MET) and calculations are performed regarding alloy development which will reduce the MET to room temperature.

Neutron beam characterization for the Moroccan TRIGA Mark II reactor

The TRIGA Mark II research reactor is equipped with four horizontal beam tubes and one thermal column. The tangential (NB1) and Percy (NB2) beam tube, which are the subject of this study, are dedicated to Prompt Gamma Neutron Activation Analysis and Neutron Imaging, and (Neutron Diffraction) facilities, respectively. A preliminary neutron characterization is needed for each beam tube. Basic beam parameters, including neutron flux, were measured with threshold activation detectors for the two beam tubes (NB1, NB2). Activity measurement through gamma spectrometry was performed with a high-purity germanium detector to evaluate the neutron flux through multiple analyses of activation detectors. The results were compared with those obtained using an approximated Monte Carlo simulation model for the reactor. A comparison between the experimental and simulated results revealed a good level of agreement.

TAAM: a reliable and user friendly tool for hydrogen-atom location using routine X-ray diffraction data.

Hydrogen is present in almost all of the molecules in living things. It is very reactive and forms bonds with most of the elements, terminating their valences and enhancing their chemistry. X-ray diffraction is the most common method for structure determination. It depends on scattering of X-rays from electron density, which means the single electron of hydrogen is difficult to detect. Generally, neutron diffraction data are used to determine the accurate position of hydrogen atoms. However, the requirement for good quality single crystals, costly maintenance and the limited number of neutron diffraction facilities means that these kind of results are rarely available. Here it is shown that the use of Transferable Aspherical Atom Model (TAAM) instead of Independent Atom Model (IAM) in routine structure refinement with X-ray data is another possible solution which largely improves the precision and accuracy of X-H bond lengths and makes them comparable to averaged neutron bond lengths. TAAM, built from a pseudoatom databank, was used to determine the X-H bond lengths on 75 data sets for organic molecule crystals. TAAM parametrizations available in the modified University of Buffalo Databank (UBDB) of pseudoatoms applied through the DiSCaMB software library were used. The averaged bond lengths determined by TAAM refinements with X-ray diffraction data of atomic resolution (dmin ≤ 0.83 Å) showed very good agreement with neutron data, mostly within one single sample standard deviation, much like Hirshfeld atom refinement (HAR). Atomic displacements for both hydrogen and non-hydrogen atoms obtained from the refinements systematically differed from IAM results. Overall TAAM gave better fits to experimental data of standard resolution compared to IAM. The research was accompanied with development of software aimed at providing user-friendly tools to use aspherical atom models in refinement of organic molecules at speeds comparable to routine refinements based on spherical atom model.

Numerical neutron attenuation correction for partially-illuminated powder samples

Chemical phase quantification from neutron diffraction measurements relies on accurate Bragg peak intensities at all diffraction angles. Amongst others these intensities are influenced by the total distance that the neutron beam has traversed through the sample in reaching the contributing volume segment and the distance from the contributing volume segment to the outer edge of the sample in the direction of the neutron detector. Since the total path length is dependent on the diffraction angle, gauge volume position inside the sample, as well as the sample dimensions and shape, the measured diffraction pattern should be corrected to account for this non-constant attenuation effect. Results show that in highly attenuation materials this can influence refined parameters during chemical phase quantification. A module was designed and integrated into the data reduction system ScanManipulator used at the neutron diffraction facility at the SAFARI-1 research reactor. The correction technique can further be used to accurately determine diffraction patterns obtained from position-resolved neutron diffraction experiments.

Materials analysis opportunities on the new neutron imaging facility IMAT@ISIS

A new neutron imaging and diffraction facility, called IMAT, is currently being commissioned at the ISIS pulsed neutron spallation source. IMAT will take advantage of neutron time-of-flight measurement techniques for flexible neutron energy selection and effective energy discrimination. The instrument will be completed and commissioned within the next few months, after neutrons have been recently delivered to the sample area. From 2016 IMAT will enable white-beam neutron radiography and tomography as well as energy-dependent neutron imaging. The facility will offer a spatial resolution down to 50 microns for a field of view of up to 400 cm2. IMAT will be operated as a user facility for material science applications and will be open for developments of time-of-flight imaging methods.

Upgrading the Neutron Radiography Facility in South Africa (SANRAD): Concrete Shielding Design Characteristics

A common denominator of all neutron radiography (NRAD) facilities worldwide is that the perimeter of the experimental chamber of the facility is a radiation shielding structure which,in some cases, also includes flight tube and filter chamber structures. These chambers are normally both located on the beam port floor outside the biological shielding of the neutron source. The main function of the NRAD-shielding structure isto maintain a radiological safe working environment in the entire beam hall according to standards set by individual national radiological safety regulations. In addition, the shielding's integrity and capability should not allow, during NRAD operations, an increase in radiation levels in the beam port hall and thus negatively affectadjacent scientific facilities (e.g. neutron diffraction facilities).As a bonus, the shielding for the NRAD facility should also prevent radiation scattering towards the detector plane and doing so, thus increase thecapability of obtaining better quantitative results. This paper addresses Monte Carlo neutron-particletransport simulations to theoretically optimize the shielding capabilities of the biological barrierfor the SANRAD facility at the SAFARI-1 nuclear research reactor in South Africa. The experimental process to develop the shielding, based on the principles of the ANTARES facility, is described. After casting, the homogeneity distribution of these concrete mix materials is found to be near perfect and first order experimental radiation shielding characteristicsthrough film badge (TLD) exposure show acceptable values and trends in neutron- and gamma-ray attenuation.

Modelling of an imaging beamline at the ISIS pulsed neutron source

A combined neutron imaging and neutron diffractionfacility, IMAT, is currently being built at the pulsed neutron spallationsource ISIS in the U.K. A supermirror neutron guide is required to combineimaging and diffraction modes at the sample position in order to obtainsuitable time of flight resolutions for energy selective imaging anddiffraction experiments. IMAT will make use of a straight neutron guide andwe consider here the optimization of the supermirror guide dimensions andcharacterisation of the resulting beam characteristics, including thehomogeneity of the flux distribution in space and energy and the average andpeak neutron fluxes. These investigations take into account some main designcriteria: to maximise the neutron flux, to minimise geometrical artefacts inthe open beam image at the sample position and to obtain a good energyresolution whilst retaining a large neutron bandwidth. All of these aredesirable beam characteristics for the proposed imaging and diffractionanalysis modes of IMAT.

R&D Efforts Towards High Field Accelerator Magnets at KEK

KEK has emphasized efforts to develop the RHQ-Nb3Al superconductor and a 13 T sub-scale magnet towards the LHC upgrade in last years. In addition, relevant R&D regarding radiation resistance has been carried out. For realization of higher field magnets beyond 15 T, thorough understanding of strain behavior of HTS and A15 superconductors is truly desired. KEK has launched a new research subject on stress/strain sensitivity of HTS and A15 superconductors in collaboration with the neutron diffraction facility at J-PARC and the High Field Laboratory in Tohoku University.

A Benchmark Study on Casting Residual Stress

A benchmark study was undertaken for casting residual stress measurements through neutron diffraction, which was subsequently used to validate the accuracy of simulation prediction. The “stress lattice” specimen geometry was designed such that subsequent castings would generate adequate residual stresses during solidification and cooling of ductile cast iron, without any cracks. The residual stresses in the cast specimen were measured using neutron diffraction. Considering the difficulty in accessing the neutron diffraction facility, these measurements can be considered as a benchmark for casting simulation validations. Simulations were performed using the identical specimen geometry and casting conditions for predictions of residual stresses. The simulation predictions were found to agree well with the experimentally measured residual stresses. The experimentally validated model can be subsequently used to predict residual stresses in different cast components. This enables incorporation of the residual stresses at the design phase along with external loads for accurate predictions of fatigue and fracture performance of the cast components.

Development of a cryogenic load frame for a neutron diffractometer

Strain measurements under loading at cryogenic temperatures are much requested for investigation of the stress/strain effect on the critical current for composite superconductors. In order to provide in-situ measurements of the lattice strain, a cryogenic load frame with a GM refrigerator has been developed, which is suitable for the neutron diffraction facility RESA equipped at JRR-3 in JAEA. The lowest temperature of 4.8 K was achieved, while the capacity of the load frame was 10 kN. Using the present cryogenic load frame, plane spacing measurement was performed under loading for two specified samples of 316 stainless steel and engineering Y–Ba–Cu–O (YBCO) coated conductor. The relation between applied stress/strain and lattice strain has been made clear in a wide range of temperatures.

Evaluation of substructure parameters by peak profile analysis of high-resolution neutron diffraction spectra

The peak profile shape analysis has been preferentially used in the evaluation of X-ray and synchrotron powder diffraction pattern. However, neutron diffraction facilities of new generation frequently offer the instrumental resolution high enough to efficiently study the effects of broadening of neutron diffraction profiles. The present paper describes the procedure for a detailed evaluation of Bragg peak shape based on the method of transformed model fitting (TMF) which has been recently developed particularly for the treatment of neutron diffraction profiles. Microstructure modeling is performed in the reciprocal space and the convolution of the model with the instrumental resolution curve is fitted to the profiles recorded in the diffraction experiment.

NET TG1: Residual stress analysis on a single bead weld on a steel plate using neutron diffraction at the new engineering instrument ‘STRESS-SPEC’

Non-destructive analysis of phase specific residual stresses and textures is only possible by diffraction methods. The new neutron diffractometer STRESS-SPEC was installed at FRM-II in Munich, Germany, for this purpose. It is designed to be equally applied to texture and residual stress analyses by virtue of its flexible configuration. The results of measurements on a single bead on plate weld within the framework of the European Network on Neutron Techniques Standardisation for Structural Integrity (NET) are presented here, in order to demonstrate the reliability and accuracy of the instrument by comparing previous results from other neutron diffraction facilities by using a Bayesian statistical approach.

Residual Strain Measurement of C/C-SiC Tubes at High Temperature

As part of the European project “high and ultrahigh temperature heat exchangers” (HITHEX) the prediction and experimental assessment of the lifetime behaviour, characterisation and qualification of particular CMC materials, including carbon fibre reinforced carbonsiliconcarbides (C/C-SiC), has been executed. Part of the programme of the HITHEX project was the measurement of the strain development within the C/C-SiC tubular specimens from room to high temperature, the results of which are presented here. Residual strains have been determined in several specimens by neutron diffraction at the High Flux Reactor (HFR) of the Joint Research Centre in Petten, The Netherlands. At the HFR two facilities are available for residual strain investigations. Both instruments were utilised in the investigations. The first facility at beam tube HB5, the combined stress and powder diffractometer, employs a constant neutron wavelength of 0.257 nm, and the second facility at HB4, the Large Component Neutron diffraction facility, LCNDF, has a flexible wavelength. The installation of a vacuum furnace has enabled the residual strain measurement of specimens at high temperature on HB4. The furnace had to fulfil three main criteria for the investigation of these specimens; high-temperature, good neutron penetration and negligible oxidation of the specimens. The ceramic specimens, which have outer and inner diameters of 50 and 40 mm, respectively, and a length of 100 mm have been measured to temperatures of up to 1450°C. Measurements were carried out in two directions on the SiC phase of several specimens, i.e. in the radial and tangential (hoop) directions. The implications of these results with respect to the structural integrity assessment of these components at high temperatures are discussed.

Neutron diffraction facilities for structural studies of crystals and fibres

Neutron diffraction facilities for structural studies of crystals and fibres

Structure determination and phase analysis by the use of neutron diffraction

Neutron diffraction has proven to be an indispensable and highly significant tool since its development 60 years ago. The neutron has unique properties that yield distinct information unavailable otherwise. Chief among these properties is the relative uniformity of the neutron scattering power of atoms across the periodic table, allowing the accurate structure determination of materials composed of widely differing atomic-number species. As sources get more powerful and computers get faster; the complexity of structures that can be solved ever increases such that protein structures with thousands of unique atomic positions can be determined. This paper reviews the state of the art in neutron diffraction experiments and facilities available to researchers.

Residual Stress Analyses Based on Neutron Diffraction in Double-V Butt Welded Steel Plates *

Residual stress measurements on a double-V butt weld joining two plates of nominally identical stainless steel have been performed using two neutron diffractometers. Sections of 270, 30 and 4 mm length cut from an original welded plate of 2.5 m length and 400 mm width were investigated using the large component neutron diffraction facility (LCNDF), at beam tube HB4, and the recently recommissioned combined powder and stress diffractometer, at beam tube HB5, at the high flux reactor (HFR) of the European Commission in Petten. Strains and stresses have been mapped in specimens of all three sizes testing the weld longitudinal, welding transverse and plate normal directions. The test results show a significant stress relaxation due to specimen cutting only in the direction normal to the cuts, e.g. from 270 to 30 mm length reduced the weld longitudinal stresses by 50%. In the other two in-plane directions the stresses were found largely unaltered.

Residual Stress Measurements in Thick Structural Weldments by Means of Neutron Diffraction*

Welding residual stresses in large structural components are a major concern with respect to their performance and lifetime. In large structures reasonable thermal stress relief treatment is usually impossible due to the component size. On the other hand, prediction of welding stresses by numerical modelling has not yet proven to be generally reliable, while the experimental determination of such stresses remains a demanding task. At the High Flux Reactor (HFR), Petten, a new residual stress diffractometer has been installed recently capable of handling of components up to 1000 kg - the Large Component Neutron Diffraction Facility (LCNDF). It has facilitated residual stress measurements in two large welded components, of which results are presented here. The first component represents a bi-metallic weld in form of a pipe of 25 mm wall thickness. Three dimensional measurements of residual stress are discussed in detail. The second specimen is a 66 mm wall thickness austenitic steel nuclear piping weld. Results on relief of strain within the weld through post weld heat treatment (PWHT) are presented. Additionally results obtained earlier at former CRNL (CAN) on a section of a thick nuclear piping weld are presented in order to illustrate the variation in the reference lattice parameter trough the weld and the heat affected zone (HAZ). These results clearly show the necessity to determine the reference parameters for each location in all measurement directions by means of measurements in small coupons free of macro-stresses.

Neutron diffraction facilities at the high flux reactor, Petten

The High Flux Reactor in Petten is equipped with twelve beam tubes for the extraction of thermal neutrons for applications in materials and medical science. Beam tubes HB4 and HB5 are equipped with diffractometers for residual stress and powder investigations. Recently at HB4 the Large Component Neutron Diffraction Facility has been installed. It is a unique facility with respect to its capability of handling heavy components up to 1000 kg in residual stress testing. Its basic features are described and the first applications on thick piping welds are shown. The diffractometer at HB5 can be set up for powder and stress measurements. Recent applications include temperature dependent measurements on phase transitions in intermetallic compounds and on Li ion energy storage materials.