Radial Collimator Research Articles

Sourcing and reducing sample environment background in low-temperature high-pressure neutron scattering experiments

Neutron scattering in high-pressure environments offers unique opportunities to measure the physical properties of matter but faces challenges due to low signal intensity and high background noise. In this study, Monte Carlo simulations were employed to identify background sources in low-temperature and high-pressure sample environments at the SINQ instrument CAMEA. Simulation results suggest that the piston pressure cell (PC) contributes significantly to the background noise in neutron scattering experiments. To counter this background, a compact radial neutron collimator was developed to reduce background in the sample environment, and its performance was evaluated experimentally. Measurements show that the collimator reduces the background generated by the PC effectively, especially for low q. Noise from the collimator was observed, and strategies to address this issue were discussed.

Development of 0.5 mm gauge size radial collimators for high-pressure neutron diffraction experiments at PLANET in J-PARC

Radial collimators with a 0.5 mm gauge size (GS) were specially designed for high-pressure neutron diffraction experiments. The performance and efficacy of these collimators, along with the 1.5 mm and 3.0 mm GS radial collimators, were investigated. The radial collimators with nominal GS of 0.75 mm, 1.5 mm, and 3.0 mm effectively exhibited GS of 0.50 mm, 1.07 mm, and 2.78 mm, respectively. The transmissions of all three radial collimators were deemed equivalent. The assessment using a Paris–Edinburgh (PE) press equipped with double-toroidal anvils and a diamond anvil cell (DAC) tailored for neutron diffraction revealed that the scattering intensity from the anvils was considerably minimized using the radial collimators and the sample-to-anvil signal ratio, as defined by the Bragg peak intensity ratio (IMgO220/IDiamond220), reached values of 0.5 and 2.0 for the PE press and DAC, respectively, when using the 0.5 mm GS radial collimators. These results indicate that the 0.5 mm GS radial collimators have been fabricated as intended and exhibit efficacy for the high-pressure-neutron diffraction experiments, specifically those exceeding 30 GPa, which cannot be reached with a PE press equipped with the standard double-toroidal anvils of a 1.5 mm cup diameter. Among those ever manufactured for neutron scattering experiments, the radial collimators display the smallest GS.

Design and performance of the high-resolution stress and texture neutron diffractometer HETU

The high-resolution stress and texture neutron diffractometer HETU at the China Mianyang Research Reactor is dedicated to measuring and analysing the residual stress and texture of engineering materials. The instrument can provide a high instrument resolution and a high neutron flux at the sample position. This article presents the HETU neutron optics design based on Monte Carlo simulation and the first assessment of its experimental performance. The technical parameters of the monochromators, slit system, radial collimators and detector were determined. A double-focusing silicon monochromator with (311) and (400) planes and a highly oriented pyrolytic graphite (HOPG) monochromator with (002) and (004) planes were selected to provide either high instrument resolution or high neutron flux modes. The highest instrument resolution of Δd/d = 1.65 × 10−3 is obtained when using Si(400), while the highest neutron flux at the sample position is 3.0 × 107 n s−1 cm−2 at the wavelength of 2.37 Å reflected by HOPG(004). The HETU diffractometer started operation in early 2022.

Residual stress measurement system of the general purpose powder diffractometer at CSNS

Neutron diffraction has become a well-established technique for the determination of residual stresses in various structural materials and bulk industrial products because of the unique deep penetration, three-dimensional mapping capability, and volume averaged bulk measurements characteristic of the scattering neutron beam. To conduct experiments in this research area, a residual stress measurement system was established on the general purpose powder diffractometer (GPPD) at the China Spallation Neutron Source (CSNS), which diffractometer now combines both powder diffraction and residual stress measurement conditions. The best d-space resolution of the diffractometer of medium-angle detector bank is Δd/d ≈ 0.33%. The gauge volume is precisely controlled by the four-blade slits, neutron Kirkpatrick–Baez (KB) mirror and radial collimators, and the general gauge volume is φ2*2 mm 3. The intelligent scanning positioning system established by GPPD achieves high-precision sample positioning, with an accuracy of up to 100μm. Until now, it has completed measurements on standard cycle samples of VAMAS shrink fit rings and plugs with known residual stress distributions, the results confirming the diffractometer’s high sensitivity and high accuracy to stress/strain gradients in materials or components. A large number of beam times are dedicated to user researches including residual stress studies of superalloys, high-entropy alloys, engineering steels, welds, and more. This demonstrates that the GPPD’s residual stress test system and the established test methods are feasible and effective.

Radial collimator performance and future collimator updates for the high-intensity total scattering diffractometer NOVA at J-PARC

The high-intensity neutron total scattering diffractometer NOVA at the Materials and Life Science Experimental Facility in the Japan Proton Accelerator Research Complex has a variety of sample environments. For background reduction, we manufactured and installed the radial collimator NOVARC with a gauge size of ∼32 mm. We evaluated its performance and succeeded in eliminating the unwanted scattering from the sample environment equipment and reducing the background signal to less than 4%. We also confirmed that G(r) data, which is important for pair distribution function analysis, is consistent with the one obtained at the sample environment with almost no background. In the future, we plan to combine NOVARC with a radial collimator manufactured using a 3D printer for measuring even smaller specimens or for extreme environments.

A flexible neutron spectrometer concept with a new ultra-high field steady-state vertical-bore magnet.

The proposed facility explores materials under ultra-high magnetic fields. By combining the power of high fields to tune materials and of neutron scattering to probe the resulting changes down to the atomic scale, this facility will enable transformative progress in the study of quantum materials and is named for the "TITAN" subset of Greek gods to reflect this transformation. TITAN will offer DC magnetic fields up to at least 20T. Exploiting the record brightness and bandwidth of the Second Target Station at the Spallation Neutron Source, TITAN will probe atomic-scale responses through high efficiency neutron spectroscopy up to 80meV energy transfer, high resolution diffraction, and small angle neutron scattering. Focusing neutron optics will maximize flux on accurately positioned samples, while radial collimation and optimized shielding and detection strategies will minimize backgrounds.

PIONEER, a high-resolution single-crystal polarized neutron diffractometer.

PIONEER is a high Q-resolution, single-crystal, polarized neutron diffractometer at the Second Target Station (STS), Oak Ridge National Laboratory. It will provide the unprecedented capability of measuring tiny crystals (0.001 mm3, i.e., x-ray diffraction size), ultra-thin films (10nm thickness), and weak structural and magnetic transitions. PIONEER benefits from the increased peak brightness of STS cold-neutron sources and uses advanced Montel mirrors that are able to deliver a focused beam with a high brilliance transfer, a homogeneous profile, and a low background. Monte Carlo simulations suggest that the optimized instrument has a high theoretical peak brilliance of 2.9 × 1012 n cm-2 sr-1 Å-1 s-1 at 2.5 Å at the sample position, within a 5 × 5mm2 region and a ±0.3° divergence range. The moderator-to-sample distance is 60m, providing a nominal wavelength band of 4.3 Å with a wavelength resolution better than 0.2% in the wavelength range of 1.0-6.0 Å. PIONEER is capable of characterizing large-scale periodic structures up to 200 Å. With a sample-to-detector distance of 0.8m, PIONEER accommodates various sample environments, including low/high temperature, high pressure, and high magnetic/electric field. A large cylindrical detector array (4.0 sr) with a radial collimator is planned to suppress the background scattering from sample environments. Bottom detector banks provide an additional 0.4 sr coverage or can be removed if needed to accommodate special sample environments. We present virtual experimental results to demonstrate the scientific performance of PIONEER in measuring tiny samples.

Neutron radial collimator using Zr–Gd alloy foil as collimating blade for engineering material diffractometer

In this study, 50-μm-thick Zr–Gd alloy foil was used as the collimating blade for a neutron radial collimator. Very thin Zr–Gd alloy foil presents excellent mechanical properties and low neutron transmission compared with a Mylar foil blade coated with gadolinium oxide (Gd2O3). The tensile strength of the 50-μm Zr–80Gd alloy foil is 135 MPa with a 4% thick tolerance, whereas the tensile strength for the 100-μm Mylar foil blade is 50 MPa with a 10% thick tolerance. The neutron transmission for 50-μm-thick Zr–80Gd alloy foil is 35.352% (1-Å neutron), which performs better than the Mylar foil blade because of the high content of gadolinium. Considering the blade thickness, the gauge volume width for different blade thicknesses was calculated analytically and optimized using McStas. The neutronic properties of a 2-mm gauge volume radial collimator with 240 blades of 50-μm Zr–80Gd alloy foils were simulated using MCNPX. The neutron-to-gamma ratio at the detector surface of the Zr–Gd alloy was higher than that of the Mylar foil blade. The transmission of the radial collimator was 93.6%, and a 2-mm gauge volume was simulated. The construction of a radial collimator using the Zr–Gd alloy blades is in progress. This shows that the Zr–Gd alloy foil provides a new type of high-quality neutron radial collimator blade.

Conceptual design of a radial collimator for MIRACLES, the time-of-flight backscattering spectrometer at the European Spallation Source

A parametrized conceptual design for a radial collimator in a neutron backscattering instrument is presented, with application to the characteristic geometry of the MIRACLES spectrometer, that will be constructed at the European Spallation Source (ESS). The analytic development of this design has considered both the forward scattering (sample-analyzer) and backscattering (analyzer-detectors) pathways. All the characteristic dimensions (internal and external radii, slit angle) and figures of merit (such as transmission and estimated background reduction) of the device are calculated as a function of the focal points. Finally, the estimated performance of the final concept has been validated by Monte Carlo simulations.

3D Printing with Mixed Powders of Boron Carbide and Al Alloy

Laser additive manufacturing with mixed powders of boron carbide and aluminum alloy is investigated. Parameters such as laser power, scan speed, scan pattern, and hatching space are systematically evaluated and optimized to obtain the desired density and porosity. These results show that the AM part contains 20 wt% boron carbide and 80 wt% aluminum alloy, which are well mixed and synthesized during the melting process. Its mechanical properties are close to those of aluminum. A thin-wall structure based two dimensional and three dimensional radial collimators were fabricated with well-controlled geometry for neutron scattering measurement.

The upgraded Polaris powder diffractometer at the ISIS neutron source.

This paper describes the design and operation of the Polaris time-of-flight powder neutron diffractometer at the ISIS pulsed spallation neutron source, Rutherford Appleton Laboratory, UK. Following a major upgrade to the diffractometer in 2010-2011, its detector provision now comprises five large ZnS scintillator-based banks, covering an angular range of 6° ≤ 2θ ≤ 168°, with only minimal gaps between each bank. These detectors have a substantially increased solid angle coverage (Ω ∼ 5.67 sr) compared to the previous instrument (Ω ∼ 0.82 sr), resulting in increases in count rate of between 2× and 10×, depending on 2θ angle. The benefits arising from the high count rates achieved are illustrated using selected examples of experiments studying small sample volumes and performing rapid, time-resolved investigations. In addition, the enhanced capabilities of the diffractometer in the areas of in situ studies (which are facilitated by the installation of a novel design of radial collimator around the sample position and by a complementary programme of advanced sample environment developments) and in total scattering studies (to probe the nature of short-range atomic correlations within disordered crystalline solids) are demonstrated.

Design of a radial collimator for the SEQUOIA direct geometry chopper spectrometer

The SEQUOIA direct geometry chopper spectrometer at the Spallation Neutron Source is considering acquisition of a radial collimator. We present here Monte-Carlo calculations examining the proposed collimator's performance. Through comparison of calculations with and without sample environments in place, one can determine appropriate parameters to use in the collimator design. The numerical results provide enough detail to determine the angular collimation for the radial collimator.

A novel 3D printed radial collimator for x-ray diffraction.

We demonstrate the use of a 3D printed radial collimator in X-ray powder diffraction and surface sensitive grazing incidence X-ray diffraction. We find a significant improvement in the overall signal to background ratio of up to 100 and a suppression of more than a factor 3 · 105 for undesirable Bragg reflections generated by the X-ray "transparent" windows of the sample environment. The background reduction and the removal of the high intensity signals from the windows, which limit the detector's dynamic range, enable significantly higher sensitivity in experiments within sample environments such as vacuum chambers and gas- or liquid-cells. Details of the additively manufactured steel collimator geometry, alignment strategies using X-ray fluorescence, and data analysis are also briefly discussed. The flexibility and affordability of 3D prints enable designs optimized for specific detectors and sample environments, without compromising the degrees of freedom of the diffractometer.

Performances of oscillating radial collimator for the Fermi chopper spectrometer 4SEASONS at J-PARC

A novel operation pattern is introduced into the oscillating radial collimator for the Fermi chopper spectrometer 4SEASONS at the Materials and Life Science Experimental Facility in J-PARC. This pattern is shown to suppress shadows originating from shielding blades of the radial collimator. We also report the transmission property of the oscillating radial collimator for 4SEASONS, based on an investigation of the scattered intensities from polycrystalline samples of different diameter.

Energy research with neutrons (ErwiN) and installation of a fast neutron powder diffraction option at the MLZ, Germany.

The need for rapid data collection and studies of small sample volumes in the range of cubic millimetres are the main driving forces for the concept of a new high-throughput monochromatic diffraction instrument at the Heinz Maier-Leibnitz Zentrum (MLZ), Germany. A large region of reciprocal space will be accessed by a detector with sufficient dynamic range and microsecond time resolution, while allowing for a variety of complementary sample environments. The medium-resolution neutron powder diffraction option for 'energy research with neutrons' (ErwiN) at the high-flux FRM II neutron source at the MLZ is foreseen to meet future demand. ErwiN will address studies of energy-related systems and materials with respect to their structure and uniformity by means of bulk and spatially resolved neutron powder diffraction. A set of experimental options will be implemented, enabling time-resolved studies, rapid parametric measurements as a function of external parameters and studies of small samples using an adapted radial collimator. The proposed powder diffraction option ErwiN will bridge the gap in functionality between the high-resolution powder diffractometer SPODI and the time-of-flight diffractometers POWTEX and SAPHiR at the MLZ.

MPISI: The neutron strain scanner materials probe for internal strain investigations at the SAFARI-1 research reactor

A modern neutron strain scanner instrument with crystallographic texture measurement capability has been established at the SAFARI-1 research reactor. This instrument, MPISI, has been benchmarked against the VAMAS Ring-and-Plug specimen, as well as in high spatial resolution mode using sub-millimeter beams. It is equipped with a double focused Si-multiwafer monochromator, sturdy high-precision sample manipulation stages, adjustable primary and secondary beam apertures interchangeable with radial collimators (RCs) on the secondary beam side and a 300 × 300 mm2 position sensitive neutron area detector. The RCs facilitate measurement of large specimens and interfaces. Variation in monochromator horizontal curvature allows optimization of the intensity (texture), resolution (peak broadening), or Figure-of-Merit (strain) with an achievable resolution of Δd/d ∼ 3 × 10−3. An Android based Wi-Fi hand-held control module in conjunction with lasers and theodolites aid with sample positioning and alignment. Data acquisition and control has been standardised on the SINQ Instrument Control Software. In-house developed data reduction software enables: flat field correction, geometric correction, vertical integration, data normalization, peak and entry-curve fitting, as well as multi-dimensional data visualization. Acquiring data against statistical criteria rather than time improves the overall instrument utilisation efficiency.

Background optimization for the neutron time-of-flight spectrometer NEAT

The neutron time-of-flight spectrometer NEAT at BER II is currently undergoing a major upgrade where an important aspect is the prevention of parasitic scattering to enhance the signal-to-noise ratio. Here, we discuss the impact of shielding to suppress parasitic scattering from two identified sources of background: the sample environment and detector tubes. By means of Monte Carlo simulations and a modification of the analytical model of Copley et al. [Copley and Cook, 1994], the visibility functions of instrument parts are computed for different shielding configurations. According to three selection criteria, namely suppression of background, transmission and detection limit, the parameters of an oscillating radial collimator are optimized for NEAT's default setup. Moreover, different configurations of detector shielding are discussed to prevent cross-talk within the radial detector system.

A combined radial collimator and cooled beryllium filter for neutron scattering

A flexible, combined, radial collimator and beryllium (Be) filter have been designed and manufactured at the Paul Scherrer Institut (PSI), Switzerland. The Be is integrated in the radial collimator by placing thin Be slices between the collimator lamellas. The filter/collimator is mounted within a vacuum vessel and dry cooled. The flexible design allows for different degrees of collimation and for different Be lengths. Results of measurements carried out at the BOA beamline at PSI are presented. These experiments include rotation scans determining the focal full width half maximum (FWHM), transmission measurements, test of different collimator lamellas and performance tests of the cooling of the filter. This new combined device will be a crucial part of the CAMEA spectrometer at SINQ, PSI.

On the design and experimental realization of a multislit-based very small angle neutron scattering instrument at the European Spallation Source

This article reports the design of a versatile multislit-based very small angle neutron scattering (VSANS) instrument working either as a dedicated instrument or as an add-on for any small-angle neutron scattering machine like the proposed SANS instrument, SKADI, at the future European Spallation Source. The use of multiple slits as a VSANS collimator for the time-of-flight techniques has been validated using McStas simulations. Various instrument configurations to achieve different minimum wavevector transfers in scattering experiments are proposed. The flexibility of the multislit VSANS instrument concept is demonstrated by showing the possibility of instrument length scaling for the first time, allowing access to varying minimum wavevector transfers with the same multislit setup. These options can provide smooth access to minimum wavevector transfers lower than ∼4 × 10−5 Å−1 and an overlapping of wavevector coverage with normal SANS mode, e.g. with the SKADI wavevector range of 10−3–1.1 Å−1. Such an angularly well defined and intense neutron beam will allow faster SANS studies of objects larger than 1 µm. Calculations have also been carried out for a radial collimator as an alternative to the multislit collimator setup. This extends the SANS Q range by an order of magnitude to 1 × 10−4 Å−1 with much simpler alignment. The multislit idea has been realized experimentally by building a prototype at Laboratoire Leon Brillouin, Saclay, with cross-talk-free geometry. Feasibility studies were carried out by making VSANS measurements with single- and multislit collimators, and the results are compared with multiple-pinhole geometry using classical SANS analysis tools.

Six-axis multi-anvil press for high-pressure, high-temperature neutron diffraction experiments.

We developed a six-axis multi-anvil press, ATSUHIME, for high-pressure and high-temperature in situ time-of-flight neutron powder diffraction experiments. The press has six orthogonally oriented hydraulic rams that operate individually to compress a cubic sample assembly. Experiments indicate that the press can generate pressures up to 9.3 GPa and temperatures up to 2000 K using a 6-6-type cell assembly, with available sample volume of about 50 mm(3). Using a 6-8-type cell assembly, the available conditions expand to 16 GPa and 1273 K. Because the six-axis press has no guide blocks, there is sufficient space around the sample to use the aperture for diffraction and place an incident slit, radial collimators, and a neutron imaging camera close to the sample. Combination of the six-axis press and the collimation devices realized high-quality diffraction pattern with no contamination from the heater or the sample container surrounding the sample. This press constitutes a new tool for using neutron diffraction to study the structures of crystals and liquids under high pressures and temperatures.