Triple-axis Neutron Spectrometer Research Articles

Evaluation of the activation of the radiation shielding of the LaDiff neutron triple-axis-spectrometer at FRM-II by simulation/calculation

Neutron radiation is widely used for investigation of matter at research reactors and spallation sources. One undesired side-effect is the production of radioactive nuclides in structure materials of the instruments (e.g. mounting structures and radiation shieldings) due to neutron capture reactions. Hence the structure materials themselves become radiation sources. The knowledge of the activities after a certain time of operation is essential for determination of the accessibility, for modifications of the instrument, for reusing the material and for waste management. It is desirable to have these data in the design phase of the instrument. One possibility to obtain the data is a combination of simulation and calculation. In this paper the simulations/calculations for the LaDiff cold triple-axis neutron spectrometer project at FRM-II (research reactor Munich) are presented. The activities in the shielding house around the experimental area of the instrument made from stainless steel and lead are considered for the cases with and without boron-carbide cover and for different Sb-contents of the lead layer. The influence of the skyshine is also considered.

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.

Design of a neutron polarizing bender for a cold triple-axis spectrometer

We report on a design study for a supermirror based neutron polarizer for a cold neutron triple-axis spectrometer to be installed at the MLZ in Garching. The spectrometer will be located at a midway position of a neutron guide, with other non-polarized instruments following downstream, such that the neutron polarizer has to be installed in the monochromatic beam downstream but close to the monochromator inside the monochromator shielding. The polarizer operates in a wavelength band 2Å –6Å . The design is optimized by ray tracing simulations with the McStas software. We compare the performance of the conventional reflection and transmission type C-benders, V-bender (kink-polarizer), S-bender, and V-cavity. The latter two will only be briefly discussed here. We also propose a new design for a transmission C-bender with additional polarizing collimators.

Current Status of the Taiwanese Cold Triple Axis Spectrometer, SIKA, at ANSTO

SIKA, a new cold neutron triple-axis spectrometer, was built on the CG4 beam port at the OPAL reactor, ANSTO. Here we report the capabilities and current status of SIKA. A versatile instrument, SIKA, provides sample environments with temperature capacities from the dilution temperature below 50 mK to the 750 K; magnetic fields of up to 12 T, the well-developed control and analysis software based on SPICE. Several scientific examples demonstrating the proficiency of SIKA are reported, such as: observation of higher harmonics in the helical magnetic phase of MnP as an example of elastic magnetic scattering; measurement of the aluminum phonon dispersion with the estimated slope of the transverse acoustic phonon at 32.4 meV; the spin-wave dispersion in MnF2 along the c axis enabled determination of exchange parameters J1 = 0.0305 meV, J2 = –0.1534 meV and D = 0.1427 meV; and observation of one of the crystal field excitations from Pr3+ in the PrFeO3 powder.

Kunpeng: A cold neutron triple-axis spectrometer at CMRR in China

A new cold neutron triple axis spectrometer named Kunpeng at the China Mianyang Research Reactor (CMRR), Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics has been constructed and fully tested. It can be typically used to study magnetic excitations, spin and lattice dynamics in condensed matter physics. In this contribution we present its main features and the first experimental data to demonstrate its performance.

Commissioning of neutron triple-axis spectrometers at HANARO

We report the status of the cold neutron triple-axis spectrometer (Cold TAS) and thermal neutron triple-axis spectrometer (Thermal TAS) installed at HANARO. Cold TAS, whose specifications are standard across the world, is in the final phase of commissioning. Proper instrument operation was confirmed through a feasibility study of phonon measurements and data analyses with resolution convolution. In contrast, Thermal TAS is in the initial phase of commissioning, and improvement of the monochromator drum is now in progress from the viewpoint of radiation shielding. In addition, we report recent activities in the development of neutron basic elements, that is, film-coated Si-wafer collimators, which are promising for use in triple-axis spectroscopy, particularly in Cold TAS.

High-resolution phonon energy shift measurements with the inelastic neutron spin echo technique

The energy resolution of the conventional way of measuring a small change in a phonon dispersion curve using neutron scattering is restricted by the relatively coarse intrinsic resolution ellipsoid of the neutron triple-axis spectrometer (TAS). By implementing inelastic neutron spin echo on the host TAS using the Larmor precession of the neutron spin, the energy resolution of such measurements can be further improved without reducing the resolution ellipsoid. Measurements of the temperature-dependent phonon energy change are demonstrated using superconducting magnetic Wollaston prisms at the HB-1 instrument of the High-Flux Isotope Reactor at Oak Ridge National Laboratory, and the achievable resolution is <10 µeV.

Development of Data Acquisition and Measurement Software for Neutron Triple Axis Spectrometer at BATAN-Serpong, Indonesia

The Neutron Scattering Laboratory at the National Nuclear Energy Agency of Indonesia (BATAN) possesses several neutron beam instruments for materials science research. One of the instruments is a neutron triple-axis spectrometer (TAS). Due to the malfunction of the main computer, the original main control system had to be replaced with a new one. For this reason, a new data acquisition and measurement software program based on GNU C++ programming language was developed for restoring the spectrometer's functionality. However, using the resulting control system, triple-axis mode experiments were very difficult to perform and their types that can be performed were limited. In order to conduct the experiments more effectively and efficiently, several improvements in both hardware and software have been developed. The Visual Basic programming language was used in developing the data acquisition and measurement software that makes it possible for all motors to move simultaneously, so that the time spent for the experiments is reduced significantly. Also, programmable motor controller cards were used for driving all the 23 motors of the instrument. All the 23 axes can be controlled by clicking the appropriate buttons or inputting text command in the main window of the software's user interface. The software has also been used to perform an elastic experiment, as well as an inelastic experiment for investigating the phenomenon of phonon. The software developed is more user friendly than the older ones, since the spectrometer status and the experiment results can be displayed in real time at the windows, and it also makes experiments more effective and efficient since the experiments can be automated and run without any user intervention until the experiments finish. /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:; mso-padding-alt:0mm 5.4pt 0mm 5.4pt; mso-para-margin:0mm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:Calibri,sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:ＭＳ 明朝; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:Times New Roman; mso-bidi-theme-font:minor-bidi;}

A mechanical rotator for neutron scattering measurements.

We have designed and built a mechanical rotation system for use in single crystal neutron scattering experiments at low temperatures. The main motivation for this device is to facilitate the application of magnetic fields transverse to a primary training axis, using only a vertical cryomagnet. Development was done in the context of a triple-axis neutron spectrometer, but the design is such that it can be generalized to a number of different instruments or measurement techniques. Here, we discuss some of the experimental constraints motivating the design, followed by design specifics, preliminary experimental results, and a discussion of potential uses and future extension possibilities.

First Magnon of BATAN’s Neutron Triple-Axis Spectrometer

The National Nuclear Energy Agency of Indonesia (BATAN) has one dedicated spectrometer for inelastic neutron scattering experiments. The instrument is a thermal neutron triple-axis spectrometer known as SN1. SN1 was installed in 1992 in the experimental hall of G. A. Siwabessy Research Reactor, Serpong, Banten. Malfunctions of the hardware and software have prevented the instrument from performing inelastic scattering measurements since 1996. The 2011-2015 five years project has been initiated to revitalize and optimize the SN1. The project serves as a preparation for the utilization of SN1 for the investigation of lattice dynamics, spin wave and magnetic excitations in condensed matters that will be started in 2016. In 2013, SN1 has successfully been repaired and was able to measure phonon dispersion relation of available single crystals, i.e ., Cu, pyrolytic graphite (PG), Ge, and Al. In 2015, the first experiment on magnetic excitation to investigate magnon dispersion relation of a known Fe single crystal has been carried out. Standard methods of inelastic scattering measurements, i.e ., a constant-energy transfer h ω with either fixed final neutron energy E f = 14.7 meV or fixed incoming neutron energy E i = 30.59 meV, and a constant momentum transfer Q with fixed incoming neutron energy E i = 30.59 meV, were applied to measure the low-energy magnetic excitations. For fixed E f measurement, a 5-cm thick PG filter was set between the sample and the analyzer to eliminate λ /n harmonics. To limit the energy and momentum spreads of the beam, collimations of 40 minutes were applied before and after the sample. The spin waves were measured along the three principal symmetry directions of [00ζ ], [ζζ 0], and [ζζζ ]. The measured magnons were compared to values in reference and were found to be in a good agreement with them. With such accomplishments, we are convinced that SN1 is now ready for its inelastic scattering application and will become one of BATAN’s neutron instrument which is routinely utilized for materials characterization on lattice dynamics and magnetic excitations by local and foreign scientists. Besides reporting the SN1 first measured magnon, the current status of SN1 instrument development will also be presented briefly. Received: 31 October 2015 ; Revised: 27 April 2016 ; Accepted: 30 April 2016

Design of the cold neutron triple-axis spectrometer at the China Advanced Research Reactor

The design of the first cold neutron triple-axis spectrometer at the China Advanced Research Reactor is presented. Based on the Monte Carlo simulations using neutron ray-tracing program McStas, the parameters of major neutron optics in this instrument are optimized. The neutron flux at sample position is estimated to be 5.6 ×107n/cm2/s at neutron incident energy Ei=5meV when the reactor operates normally at the designed 60MW power. The performances of several neutron supermirror polarizing devices are compared and their critical parameters are optimized for this spectrometer. The polarization analysis will be realized with a flexible switch from the unpolarized experimental mode.

Inelastic neutron scattering and ab initio studies of cyclotrimethylenetrinitramine

As an important secondary explosive, cyclotrimethylenetrinitramine (RDX, C3H6O6N6) is extensively used in military and industrial applications due to its high energy density and low sensitivity to external stimulations. Considerable attention has been devoted to the study of the detonation initiation, with particular interest in the mechanism by which energy is transferred from a shock wave to the internal molecular vibrations so as to begin endothermic decomposition. During the whole process, phonons as the primary carriers of heat may play an important role. Experimentally, inelastic neutron scattering (INS) technique provides a means of studying the dynamics of motions of atoms and molecules in the crystal, especially in the low frequency region which contains most phonon lattice modes. In this work, neutron diffraction pattern of polycrystalline RDX under ambient condition has been measured and compared with the calculated results, showing reasonable agreement with and thus confirming the structure of RDX. Subsequently, the vibrational INS spectrum of RDX has been measured at T=10 K over the region of 10-104~cm-1 by using cold neutron triple-axis spectrometer. On the basis of the solid-state density functional calculations with the generalized gradient approximation (BLYP and BP functionals), it is possible to perform normal-mode analysis, which agrees with previous assignments. A total of 9 phonon lattice modes and 3 internal vibrations have been identified. Eight possible doorway modes may be predicted in the energy range between 100 and 148~cm-1, which arise from the combinations of phonon lattice modes 38.3, 40.3, 50.2, 61.5~cm-1 and fundamental vibrations 86.6, 88.6, 101.4~cm-1. The doorway modes are the proposed bridge by which the energy of initial shockwave can pass from the external degrees of freedom into those of the molecule. It is shown that all of these eight modes have fundamental vibrational components that consist of nitro-group deformation vibrations. This point is of particular importance and supports the theory that the initial bond broken in detonation is the NN bond. This work may shed light on the mechanism of detonation initiation from a microscopic viewpoint.

Neutron resonance spin-echo upgrade at the three-axis spectrometer FLEXX.

We describe the upgrade of the neutron resonance spin-echo setup at the cold neutron triple-axis spectrometer FLEXX at the BER II neutron source at the Helmholtz-Zentrum Berlin. The parameters of redesigned key components are discussed, including the radio frequency (RF) spin-flip coils, the magnetic shield, and the zero field coupling coils. The RF-flippers with larger beam windows allow for an improved neutron flux transfer from the source to the sample and further to the analyzer. The larger beam cross sections permit higher coil inclination angles and enable measurements on dispersive excitations with a larger slope of the dispersion. Due to the compact design of the spin-echo units in combination with the increased coil tilt angles, the accessible momentum-range in the Larmor diffraction mode is substantially enlarged. In combination with the redesigned components of the FLEXX spectrometer, including the guide, the S-bender polarizer, the double focusing monochromator, and a Heusler crystal analyzer, the count rate increased by a factor of 15.5, and the neutron beam polarization is enhanced. The improved performance extends the range of feasible experiments, both for inelastic scattering on excitation lifetimes in single crystals, and for high-resolution Larmor diffraction. The experimental characterization of the instrument components demonstrates the reliable performance of the new neutron resonance spin-echo option, now available for the scientific community at FLEXX.

The use of selected neutron absorption resonance filters to suppress spurious events on hot neutron spectrometers

Resonant absorption can be used as a filter for high energy neutron spectroscopy. Here we report the transmission of eight thin foil filters: erbium, indium, iridium, dysprosium, hafnium, gadolinium, cadmium and samarium, measured using neutron time-of-flight techniques over a range of energies (1meV to 10eV). Measured transmission is converted into energy-dependent absorption cross-section which compares closely to tabulated values. Each resonance is characterized from 91meV (samarium) to 2815meV (gadolinium) by Lorentzian fits. Possibilities for the use of neutron filters depending on the type of spurious background are discussed and the performance is simulated for a specific example of a hot neutron triple axis spectrometer experiment.

The upgraded cold neutron triple-axis spectrometer FLEXX – enhanced capabilities by new instrumental options

The upgrade of the cold neutron triple axis spectrometer FLEXX, a work-horse instrument for inelastic neutron scattering matching the sample environment capabilities at Helmholtz-Zentrum Berlin, has been successfully accomplished. Experiments confirmed an order of magnitude gain in flux now allowing for intensity demanding options to be fully exploited at FLEXX. In this article, we describe the layout and design of two newly available FLEXX instrument options in detail. The new Heusler analyzer gives an increase of the detected polarized neutron flux due to its superior focusing properties, significantly improving the feasibility of future polarized and neutron resonance spin echo experiments. The MultiFLEXX option provides simultaneous access to large regions in wavevector and energy space for inelastic excitations thus adding mapping capabilities to the spectrometer.

A novel neutron spin echo technique for measuring phonon linewidths using magnetic Wollaston prisms

A new method of implementing neutron spin echo measurement of phonon linewidths on a triple-axis neutron spectrometer is introduced, based on recently developed superconducting magnetic Wollaston prisms. Each arm of the spectrometer is composed of two Wollaston prisms with a rectangular field region between them. By introducing triangular and rectangular field regions, loci of constant spin echo phase can be manipulated easily to achieve the so-called phonon focusing condition. Unlike the neutron resonance spin echo method, which is tuned by physically tilting the field boundaries, the new device can be tuned electromagnetically to achieve the phonon focusing condition. By adjusting the field configurations, the linewidths of phonon excitations with high energy and large group velocity can be measured. By employing superconducting films to define the various field regions, high neutron transmission and good neutron polarization efficiency can be obtained.

Surveying the higher dimensions of the aperiodic composite nonadecane/urea

We recently observed for the first time that there exist phase transitions where the structural changes correspond just to degrees of freedom hidden in the internal (super)space of an aperiodic material, here the composite nonadecane/urea [1]. A key factor in the discovery of this type of transition [2] was the examination of the diffraction pattern in 3D, only possible at the time on a four-circle triple-axis neutron spectrometer, the analyzer used in zero-energy transfer to reduce the background and improve resolution. Despite the greater accessibility in reciprocal space, the weak intensity of the superlattice reflections limited the volume of reciprocal space that could be explored. Modern neutron Laue diffractometers with large image-plate detectors permit rapid and extensive exploration of reciprocal space with high resolution in the two-dimensional projection and a wide dynamic range with negligible bleeding of intense diffraction spots [3]. Surveying nonadecane/urea with neutron Laue diffraction from 300K to 4K reveals further detail of the superspace-driven phase transition, notably an increase in misorientation in the plane perpendicular to the composite misfit axis, as well as a first-order transition to a new phase at lower temperature. These new observations shed further light on how nature can use the degrees of freedom hidden in the internal superspace to form states that cannot be envisaged in the usual 3D real space.

냉중성자 삼축분광장치의 차폐능 최적화 설계 및 선량 측정

A new cold neutron triple-axis spectrometer (Cold-TAS) was recently constructed at the 30 MWth research reactor, HANARO. The spectrometer, which is composed of neutron optical components and radiation shield, required a redesign of the segmented monochromator shield due to the lack of adequate support of its weight. To shed some weight, lowering the height of the segmented shield was suggested while adding more radiation shield to the top cover of the monochromator chamber. To investigate the radiological effect of such change, we performed MCNPX simulations of a few different configurations of the Cold-TAS monochromator shield and obtained neutron and photon intensities at 5 reference points just outside the shield. Reducing the 35% of the height of the segmented shield and locating lead 10 cm from the bottom of the top cover made of polyethylene was shown to perform just as well as the original configuration as radiation shield excepting gamma flux at two points. Using gamma map by MCNPX, it was checked that is distribution of gamma. Increased flux had direction to the top and it had longer distance from top of segmented shield. However, because of reducing the 35% of the height, height of dissipated gamma was lower than original geometry. Reducing the 35% of the height of the segmented shield and locating lead 10cm from the bottom of the top cover was selected. After changing geometry, radiation dose was measured by TLD for confirming tester`s safety at any condition. Neutron(0.21 ) and gamma(3.69 ) radiation dose were satisfied standard(6.25 ).

Gains from the upgrade of the cold neutron triple-axis spectrometer FLEXX at the BER-II reactor

The upgrade of the cold neutron triple-axis spectrometer FLEXX is described. We discuss the characterisation of the gains from the new primary spectrometer, including a larger guide and double focussing monochromator, and present measurements of the energy and momentum resolution and of the neutron flux of the instrument. We found an order of magnitude gain in intensity (at the cost of coarser momentum resolution), and that the incoherent elastic energy widths are measurably narrower than before the upgrade. The much improved count rate should allow the use of smaller single crystals samples and thus enable the upgraded FLEXX spectrometer to continue making leading edge measurements.

Inelastic neutron scattering study of the lattice dynamics of LaCoO3

The lattice dynamics of lanthanum cobaltite is investigated using the coherent inelastic neutron scattering technique in a temperature range from 10 to 536 K, in which two phase transitions are observed: a change in the Co spin state and a metal-insulator phase transition. The measurements were performed using an IN8 high flux thermal neutron triple-axis spectrometer (ILL, Grenoble). Temperature changes in the phonon dispersion curves caused by the rearrangement of the electron and spin subsystems are found.