Velocity Selector Research Articles

Quality assessment of the wide-angle detection option planned at the high-intensity/extended Q-range SANS diffractometer KWS-2 combining experiments and McStas simulations.

For a reliable characterization of materials and systems featuring multiple structural levels, a broad length scale from a few ångström to hundreds of nanometres must be analyzed and an extended Q range must be covered in X-ray and neutron scattering experiments. For certain samples or effects, it is advantageous to perform such characterization with a single instrument. Neutrons offer the unique advantage of contrast variation and matching by D-labeling, which is of great value in the characterization of natural or synthetic polymers. Some time-of-flight small-angle neutron scattering (TOF-SANS) instruments at neutron spallation sources can cover an extended Q range by using a broad wavelength band and a multitude of detectors. The detectors are arranged to cover a wide range of scattering angles with a resolution that allows both large-scale morphology and crystalline structure to be resolved simultaneously. However, for such analyses, the SANS instruments at steady-state sources operating in conventional monochromatic pinhole mode rely on additional wide-angle neutron scattering (WANS) detectors. The resolution must be tuned via a system of choppers and a TOF data acquisition option to reliably measure the atomic to mesoscale structures. The KWS-2 SANS diffractometer at Jülich Centre for Neutron Science allows the exploration of a wide Q range using conventional pinhole and lens focusing modes and an adjustable resolution Δλ/λ between 2 and 20%. This is achieved through the use of a versatile mechanical velocity selector combined with a variable slit opening and rotation frequency chopper. The installation of WANS detectors planned on the instrument required a detailed analysis of the quality of the data measured over a wide angular range with variable resolution. This article presents an assessment of the WANS performance by comparison with a McStas [Willendrup, Farhi & Lefmann (2004). Physica B, 350, E735-E737] simulation of ideal experimental conditions at the instrument.

Incident beamline design for a modern cold triple axis spectrometer at the High Flux Isotope Reactor

A modern cold triple axis spectrometer is being planned for the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Here, we describe the design of an incident beamline that will put a flux of ∼108ncm2s on a sample with an area of 2 cm × 2 cm. It takes current physical constraints at HFIR into account and it can accommodate both single and multiplexed analyzer-detector secondary spectrometers and large superconducting magnets. The proposed incident beamline includes a multi-channel guide with horizontal focusing, a neutron velocity selector, components to facilitate an incident beam polarization option, and a double-focusing pyrolytic graphite monochromator. This work describes the process of optimizing the guide system and monochromator and summarizes the expected performance of the incident beamline for non-polarized operation.

Design and validation of a neutron double crystal monochromator for ICON

Many applications using neutron imaging for materials science use diffraction-based contrast to explore and understand the condition of the samples. Diffraction-based methods require wavelength resolution. The neutron imaging instrument ICON at Paul Scherrer Institut has, until recently, only provided this functionality using a velocity selector. We designed a new double crystal monochromator (DCM) for the conditions at ICON as an option to meet the wavelength resolution demands of specific advanced methods such as diffraction contrast neutron imaging. The DCM can also be combined with the velocity selector. The device uses two pyrolitic graphite crystals as active components, allowing the selection of wavelengths in the interval 2–6 Å. This wavelength interval covers the main applications for wavelength-selective imaging considered at ICON. The device is designed for installation near the instrument shutter system. This position has the advantage that the effective field of view is maximized at the experiment position due to the beam divergence of the ICON. On the other hand, this position means that the beam displacement relative to the initial beam is relatively short. Thus, shielding is vital for the installation. We describe the device design and show the results from the first characterization experiments.

ASTOR: the imaging beamline of the Argentine Neutron Beam Laboratory

The ASTOR instrument is a state-of-the-art neutron imaging instrument being developed by LAHN (Laboratorio Argentino de Haces de Neutrones or Argentinian Laboratory of Neutron Beams) to be installed on one of the cold neutron beams of the 30MW open pool reactor RA-10, currently under construction at the outskirts of Buenos Aires. ASTOR will have direct view to a D2 cold source and will include a primary collimator at 2.5m from its surface. Its design includes a beam conformation room with a set of exchangeable secondary collimators to further collimate the beam, and several devices (solid state filters, a velocity selector and a double crystal monochromator) to tailor the energy spectrum for specific applications. Downstream the beam, it will have an experimental room with ample space for objects and samples, and L/D ratios in the range 120-1500 with calculated fluxes of 3.7x108 n/cm2s and 2.4x106 n/cm2s respectively (E<25meV) and a maximum field of view of 25x25 cm2. It will also count with two rectangular pinholes to obtain increased resolution in one dimension without substantially decreasing the flux.

Monte Carlo simulations of LUOSHU: a new 46-meter small-angle neutron scattering instrument in China

The LUOSHU small-angle neutron scattering spectrometer is one of the neutron scattering instruments under construction at China Mianyang Research Reactor. Quantitative characterization of nanoparticles is now in a higher demand for research interests in material science, physics, chemistry, biology. Therefore, as a general-purpose small-angle scattering spectrometer, LUOSHU is aimed to provide a large accessible Q range, flexible resolution and sufficient neutron flux. Monte Carlo simulations have been performed on LUOSHU from the neutron source to sample platform to optimize the parameters of the bender part, collimation system, and the velocity selector. And the instrument layout is optimized base on the simulation results. Finally, the maximum neutron intensity of the neutron beam at the sample stage can reach 1.01 × 107 N·s-1·cm-2 and its divergence is 0.63.

Extending MIEZE spectroscopy towards thermal wavelengths.

A modulation of intensity with zero effort (MIEZE) setup is proposed for high-resolution neutron spectroscopy at momentum transfers up to 3 Å-1, energy transfers up to 20 meV and an energy resolution in the microelectronvolt range using both thermal and cold neutrons. MIEZE has two prominent advantages compared with classical neutron spin echo. The first is the possibility to investigate spin-depolarizing samples or samples in strong magnetic fields without loss of signal amplitude and intensity. This allows for the study of spin fluctuations in ferromagnets, and facilitates the study of samples with strong spin-incoherent scattering. The second advantage is that multi-analyzer setups can be implemented with comparatively little effort. The use of thermal neutrons increases the range of validity of the spin-echo approximation towards shorter spin-echo times. In turn, the thermal MIEZE option for greater ranges (TIGER) closes the gap between classical neutron spin-echo spectroscopy and conventional high-resolution neutron spectroscopy techniques such as triple-axis, time-of-flight and back-scattering. To illustrate the feasibility of TIGER, this paper presents the details of its implementation at the RESEDA beamline at FRM II by means of an additional velocity selector, polarizer and analyzer.

Cold neutron triple-axis spectrometer (Cold TAS) at HANARO

A cold neutron triple-axis spectrometer (Cold TAS) has been installed in HANARO at the Korea Atomic Energy Research Institute, South Korea. It has been designed for high-resolution inelastic-neutron-scattering (INS) measurements of spin and lattice dynamics using a neutron velocity selector (NVS) for incident cold neutrons. We evaluated the wavelength resolution and harmonics filtration of the NVS and verified the vertical focusing effects of the pyrolytic-graphite crystal monochromator. The beam flux at the sample position and the spectrometer resolution, which are key factors in INS experiments, attained the typical TAS specification. Finally, we exemplified INS spectra to show the current performance of the high-resolution mode and magnetic-excitation measurements.

A concept of a broadband inverted geometry spectrometer for the Second Target Station at the Spallation Neutron Source.

BWAVES is an acronym for Broadband Wide-Angle VElocity Selector spectrometer, indicating that a novel WAVES (Wide-Angle VElocity Selector) device will be used to select the velocity/wavelength of the detected neutrons after they are scattered by the sample. We describe a conceptual design of BWAVES, a time-of-flight broadband inverted-geometry neutron spectrometer for the Second Target Station at the Spallation Neutron Source operated by Oak Ridge National Laboratory. Being the first inverted geometry spectrometer where the energy of the detected neutrons can be chosen by a WAVES device mechanically, irrespective of the limitations imposed by the crystal analyzers or filters, BWAVES will feature a uniquely broad, continuous dynamic range of measurable energy transfers, spanning 4.5 decades. This will enable measurements of both vibrational and relaxational excitations within the same, continuous scattering spectra. Novel approaches that are necessary for the implementation of a WAVES device at the BWAVES spectrometer will result in a spectrometer with the design and characteristics much different from those displayed by the neutron spectrometers in existence today.

Broadband Wide-Angle VElocity Selector (BWAVES) neutron spectrometer designed for the SNS Second Target Station

A recently proposed wide-angle velocity selector (WAVES) device for choosing the velocity of detected neutrons after they have been scattered by the sample paves the way for inverted geometry neutron spectrometers with continuously adjustable final neutron wavelength. BWAVES broadband inverted geometry spectrometer proposed for the Second Target Station at the Spallation Neutron Source at Oak Ridge National Laboratory is designed using WAVES to simultaneously probe dynamic processes spanning 4.5 decades in time (energy transfer). This makes BWAVES a uniquely flexible instrument which can be viewed as either a quasielasitc neutron scattering (QENS) spectrometer with a practically unlimited (overlapping with the vibrational excitations) range of energy transfers, or a broadband inelastic vibrational neutron spectrometer with QENS capabilities, including a range of accessible momentum transfer (Q) and a sufficiently high energy resolution at the elastic line. The new capabilities offered by BWAVES will expand the application of neutron scattering in ways not possible with existing neutron spectrometers.

Multiple scattering and resolution effects in small-angle neutron scattering experiments calculated and corrected by the software package MuScatt.

This article deals with multiple scattering effects that are important for the method of small-angle neutron scattering (SANS). It considers three channels for the coherent elastic, the incoherent elastic and the incoherent inelastic scattering processes. The first channel contains the desired information on the experiment. Its multiple scattering effects can be desmeared, as shown in the later sections of the article. The other two channels display a nearly constant background as a function of the scattering angle. The incoherent elastic scattering is treated by the theory of Chandrasekhar, allowing for multiple scattering even at large scattering angles. The transfer to a single representative thermalized wavelength by the inelastic scattering - as a simplification - is assumed to happen by a single scattering event. Once the transition to this altered wavelength has happened, further incoherent multiple scattering is considered. The first part of the paper deals with the multiple scattering effects of light water. In the later part of the article, deconvolution algorithms for multiple scattering and instrumental resolution of the elastic coherent signal as implemented in the program MuScatt are described. All of these considerations are interesting for both reactor-based instruments with velocity selectors and time-of-flight SANS instruments and may improve the reliability of the data treatment.

Sensitivity analysis of the transmission factor and resolution of a multiblade neutron velocity selector to the various parameters

The neutron velocity selector is a device used to produce a monochromatic neutron beam with continuous flux. The purpose of the present study is to investigate the sensitivity of the transmission factor and resolution of a multiblade neutron velocity selector to the various parameters using the McStas software. To this end, two instruments were created using the Arm, Progress_bar, Source_simple, DivMonitor, L_monitor, Guide_channeled and V_selector components of the McStas software. The used V_selector component to simulate the multiblade neutron velocity selector was created by considering three assumptions: 1. The absorption of colliding neutrons to selector blades, 2. No interaction of the neutron with input and output windows of the selector, and 3. The absorption of neutrons that pass through selector blades, but do not reach the output window of the selector due to great divergence.As a result of the simulations, the transmission factor and resolution of the multiblade selector for the case that the neutron beam entered into the selector have a uniform angular distribution with divergence 6'. The calculated transmission factor and resolution are 94.29 ± 0.05 and 10.52 ± 0.01, respectively. A comparison of these results with the reported experimental values in the reference paper shows that the relative error of the transmission factor and resolution are (0.31± 0.05) % and (5.2± 0.05) %, respectively.

A Ioffe Trap Magnet for the Project 8 Atom Trapping Demonstrator

The goal of the Project 8 experiment (B. Monreal and J. Formaggio, 2009) is to measure the absolute neutrino mass using tritium, which involves precisely measuring the energies of the beta-decay electrons in the high-energy tail of the spectrum (A. A. Esfahani et al. , 2017). The experimental installation of Project 8 Atom Trapping Demonstrator requires a magnet with rather unusual field properties. The magnet has to contain within the cold mass a large volume enclosed by a continuous, uninterrupted boundary higher than 2 T, whereas the field in a substantial volume inside this boundary has to be of the order of 10−4 T or less. A 1-T solenoid field provides the background field necessary for the detection of the beta-decay electrons (A. A. Esfahani et al. , 2019). A proposed toroidal magnet system [a Ioffe-Pritchard trap (T. Bergeman et al. , 1987)] comprised of specially shaped multiple racetrack windings with opposing polarities satisfies these unusual requirements. The magnet is made of NbTi wire and expected to be conduction cooled. Manufacturability issues are addressed as well as the effect of tolerances on the field quality. The design includes additional topological features providing a low-field duct for interfacing with the peripheral coils of the velocity and state selector.

Testing and evaluation of velocity selector control system of small angle neutron scattering spectrometer

Testing and evaluation of velocity selector control system of small angle neutron scattering (SANS) spectrometer has been done. It applied a unit of speed control variable AC, Optidrive Invertek Drives. This system is designed to be manually controlled and computerized. To control the Optidrive in manual mode, it can be done by keypad on the unit. The Optidrives can be controlled using computer by connecting the unit into a computer via USB port and OptiTools Studio software. Optidrive Invertek Drives need alternative current (AC) voltage one phase 220 volt with three phase out 220 volt. This out voltage is used as voltage source for moving the motor of disk in SANS neutron velocity selector. The speed of the disk in SANS neutron velocity selector is changed by adjusting the frequency from the Optidrive Invertek Drives. The numbers of speed of the disk determine the neutron wavelength passed through SANS neutron velocity selector. It is observed that every increasing frequency of 1 Hz, it will increase the disk speed by 59.929 rpm. The calibration that has been done for this system using silver behenate, obtain wavelength of the neutrons dependent to the disk speed. They are 3.10, 3.09, 3.41, 3.76, 4.23, 4.71, and 5.39 Å for disk speed 6500, 6000, 5500, 5000, 4500, 4000, and 3500 rpm respectively.

A series of neutron time of flight method applications on the China Advanced Research Reactor

The advantages of time of flight method enable it to be widely used on stationary reactors. In this study, we reported several typical applications of time of flight method on the China Advanced Research Reactor (CARR). First, a new solution is designed to measure the beam characteristics including wavelengths, wavelength resolution rates and intensities of HOPG(002) monochromator for the unfiltered and filtered cases. Second, the changes in neutron wavelength spectra on the cross section of curved neutron guide CNGB end were examined and studied. It can be concluded that evident shape changes between neutron wavelength spectra along horizontal direction are mainly caused by the horizontal curving of curved neutron guide and dips at other wavelengths apart from 4 Å are mainly caused by small radius of curvature of curved neutron guide. Third, based on neutron velocity selector of small angle neutron scattering instrument at CARR, a calibration instrument is designed, and calibration experiments are conducted and simulated. The results indicate that the discrepancy between the experimental wavelength resolution rate and the theoretical one is caused by beam divergence linked with the critical reflection angle of neutron guide coating and the difference between experimental wavelength and the theoretical one is caused by the shape change of source neutron wavelength spectrum. These findings are reported here for the first time.

Upgrade of a small-angle neutron scattering spectrometer Suanni of China Mianyang Research Reactor

The small-angle neutron scattering spectrometer, SANS-Suanni, of the 20 MW China Mianyang Research Reactor (CMRR), was upgraded recently to improve its performance and anti-risk capability. The major modifications include: (i) installing a new mechanical velocity selector consisting of a rotor with helical slots; (ii) a replacement of the front of the detector tank to decrease the minimum sample-to-detector distance; (iii) installing a laser locator and a set of fixed lenses in collimator chamber. After the modifications, firstly, a higher maximum-q (qmax) can be achieved up to 6.3 nm−1. With the help of rotating the detector tank, qmax can be further increased to 10.5 nm−1. Secondly, a higher neutron flux at sample position up to 1.18 ×107 cm−2s−1 (at neutron wavelength of 0.53 nm) is obtained. Thirdly, a convenient and user-friendly beam center finding operation for environmental devices is available. The actual performance after the modifications is demonstrated with the measurements of standard samples.

QUOKKA, the pinhole small-angle neutron scattering instrument at the OPAL Research Reactor, Australia: design, performance, operation and scientific highlights

QUOKKA is a 40 m pinhole small-angle neutron scattering instrument in routine user operation at the OPAL research reactor at the Australian Nuclear Science and Technology Organisation. Operating with a neutron velocity selector enabling variable wavelength, QUOKKA has an adjustable collimation system providing source–sample distances of up to 20 m. Following the large-area sample position, a two-dimensional 1 m2 position-sensitive detector measures neutrons scattered from the sample over a secondary flight path of up to 20 m. Also offering incident beam polarization and analysis capability as well as lens focusing optics, QUOKKA has been designed as a general purpose SANS instrument to conduct research across a broad range of scientific disciplines, from structural biology to magnetism. As it has recently generated its first 100 publications through serving the needs of the domestic and international user communities, it is timely to detail a description of its as-built design, performance and operation as well as its scientific highlights. Scientific examples presented here reflect the Australian context, as do the industrial applications, many combined with innovative and unique sample environments.

Theory of Electromagnetism and Gravity —Modeling Earth as a Rotating Solenoid Coil

Presented in this manuscript are conventional electrical engineering tools to model the earth as a rotating electrical machine. Calculations using known parameters of the earth and measured field data has resulted in new understanding of the earth’s electrical system and gyroscopic rotation. The material makeup of the inner earth is better understood based on derived permeability and permittivity constants. The planet has been modeled as simple coils and then as a parallel impedance circuit which has led to fundamental insight into planetary speed control and RLC combination for Schumann Resonance of 7.83 Hz. Torque and Voltage Constants and the inverse Speed Constant are calculated using three methods and all compare favorably with Newton’s Gravitational Constant. A helical resonator is referenced and Schumann’s Resonant ideal frequency is calculated and compared with others idealism. A new theory of gravity based on particle velocity selector at the poles is postulated. Two equations are presented as the needed links between Faraday’s electromagnetism and Newtonian physics. Acceleration and Deceleration of earth is explained as a centripetal governor. A new equation for planetary attraction and the attraction of atomic matter is theorized. Rotation of the earth’s electrical coil is explained in terms of the Richardson effect. Electric power transfer from the sun to the planets is proposed via Flux Transfer Events. The impact of this evolving science of electromagnetic modeling of planets will be magnified as the theory is proven, and found to be useful for future generations of engineers and scientists who seek to discover our world and other planets.

Optimization of measurements at neutron reflectometers

New optimization criteria for a class of instruments, neutron reflectometers, are established by analysis of the reflectivity measurements. Luminosity of the reflectometer is defined as the neutron flux incident onto the sample surface on conditions that the measurement is made with a given momentum transfer resolution. The correct choice of the working wavelength and realization of measurements with optimum parameters of the neutron beam increase luminosity in several times. Standard schemes for the reflectivity measurements with monochromatic and white beams are considered. Optimization of the reflectivity measurements generally requires numerical calculations. Analytically, its potential is demonstrated by considering thermalized neutron beams. Such innovations as neutron-optical velocity selector, small-angle Soller collimators with traps for neutrons reflected from the channel walls and neutron fan beam time-of-flight technique are proposed to further increase the luminosity of reflectometers.

Neutron reflectometry: Filling Δq with neutrons

Luminosity of the reflectometer is defined as the neutron flux incident onto the sample surface for measurements made with a given momentum transfer resolution Δq. The filling of Δq with neutrons near a certain q depends not only on the source luminance and the source-sample tract transmittance, but also on the neutron beam tailoring. The correct choice of the working wavelength and measurements with optimum neutron beam parameters increase luminosity in several times. New optimization criteria for neutron reflectometers are suggested. Standard schemes of the reflectivity measurement with monochromatic and white beams are re-examined. Optimization of reflectivity measurements generally requires numerical calculations. Analytically, its potential is demonstrated by considering thermalized neutron beams. Such innovations as velocity selector on the basis of aperiodic multilayers, small angle Soller collimator with traps for neutrons reflected from the channel walls and fan beam time-of-flight technique are proposed to further increase the luminosity of reflectometers.

The upgrade of the cold neutron three-axis spectrometer IN12 at the ILL

After nearly 40years of successful operation the cold three-axis spectrometer IN12 at the Institut Laue-Langevin, Grenoble, France, has been relocated to a new position and the primary spectrometer has been upgraded. Latest modern optical components are employed. A new guide in combination with a virtual source concept and a double focusing monochromator guarantee highest flux. With its high unpolarized and polarized neutron flux IN12 allows for demanding experiments. A velocity selector in the guide ensures a clean beam and a very low background. A gain in flux of about an order of magnitude at the sample position has been achieved compared to the previous instrument and IN12׳s wavelength range now extends far into the warmish region.