ISIS Pulsed Neutron Research Articles

Development of a multi-layer high-efficiency GEM-based neutron detector for spallation sources

Neutron detection is nowadays mostly based on 3He gas detectors, but its shortage and the continuous upgrades of the neutron facilities require new devices to perform experiments with maximum performances. This work presents a new detector based on the Gas Electron Multiplier (GEM) combined with several boron layers. This detector combines the features of GEM technology with the properties of boron as a neutron converter and the device is produced to sustain high neutron fluxes with high detection efficiency. The detector has been characterised at the ISIS Pulsed Neutron and Muon Source (UK). Based on the analysis of our results, the detector has shown a good response to thermal and epithermal neutrons reaching a detection efficiency of 16% at 1.8 Å (25 meV). The good detection efficiency (even increasable with the addition of further boron GEM foils) and the good time resolution, make the detector a unique device for the neutron techniques. In particular, its use can easily be envisaged in techniques involving neutron transmission measurements, that require high fluxes impinging on the detectors, with the added bonus of a 2D-resolved capability due to the padded anode.

Real-time pulse shape discrimination for neutron scattering science using EJ-270

A detector for neutron scattering applications utilizing the 6Li loaded pulse shape discrimination scintillator EJ-270 was developed. The detector utilises a pulse shape discrimination algorithm developed for high-count rate applications implemented in FPGA to enable real time operation. The implemented algorithm we call Tail Sum was specifically developed for high-rate thermal neutron detection and implemented into a 2 channel 500 MSps 14-bit ADC with a Xilinx Kintex 7 K325T FPGA. The detector consisted of a 48 mm diameter × 15 mm thick cylinder of EJ-270 mounted on a Hamamatsu R6231-100 PMT and an E1198-2 base at -1000 V. The performance of the system was evaluated using a moderated 241Am-Be mixed radionuclide source, a figure of merit of 1.605 ± 0.007 was measured. The γ-ray sensitivity of the system was measured using a 60Co source and found to be 3.23 × 10-6 ± 7 × 10-8. The high neutron count rate capability of the system was tested on the Emma instrument at the ISIS pulsed neutron and muon source based at the Rutherford Appleton Laboratory, a peak count rate of 5 × 105 neutrons per second was measured on a single channel and was found to have no statistically significant deviation from the expected count-rate.

Hydrogen Detection Limits and Instrument Sensitivity of High-Resolution Broadband Neutron Spectrometers.

The limits of detection (LOD) and quantitation (LOQ) in the mass domain, for broadband vibrational spectroscopy with neutrons on the TOSCA spectrometer at the ISIS Pulsed Neutron and Muon Source (UK), have been studied. The well-known 3σ and 10σ approaches are used through a specifically developed analytical procedure that is based on the calculation of the integrated spectral intensities in selected energy-transfer ranges, as a function of mass of standard reference materials and calibrants, such as ZrH2, 2,5-diiodothiophene, and low-density polyethylene. The analysis shows that the blank, that is, the instrument setup without the analyte, plays a critical role in the measurement performance, especially for small specimen quantities. The results point that TOSCA enables detection of 128 μmol (LODH) and quantitation of 428 μmol (LOQH) of elemental hydrogen analytes in ZrH2. The determined values for this and other standards allow for the assessment of the calibration curve design and instrument sensitivity and define a method to be used for inelastic neutron scattering spectrometers such as TOSCA, or VESPA, the new beamline under construction at the European Spallation Source in Lund (Sweden).

Neutron-based techniques for archaeometry: characterization of a Sardinian boat model

Sardinian metallurgy produced samples of high artistic and historical value. In particular, ship models are rare and unmatched examples of the mastery reached by Sardinian metallurgists and their production process deserves an in-depth analysis of all the phases involved in the making. In this work, we examined a Sardinian boat model to obtain information about its composition, microstructure and manufacturing technique. The object is a small bronze ship model that was found near the Nuraghe Colovros, located in north-east Sardinia (Italy). It was analysed by means of neutron imaging and neutron diffraction experiments at the ISIS Pulsed Neutron and Muon Source laboratory (Harwell, UK). Neutron techniques are relatively new in the field of archaeometry, but they are a very effective tool for the study of archaeological objects: they permit to survey complete artefacts, determine compositions and structures, assess the conservation status and address questions of effective use and casting techniques. This type of data can add new and different insights to existing archaeological information, especially where sampling is not permitted. The outcome of the study reveals a peculiar approach to the manufacturing of the boat model.

Apparatus for simultaneous dynamic light scattering-small angle neutron scattering investigations of dynamics and structure in soft matter.

Dynamic Light Scattering (DLS) and Small-Angle Neutron Scattering (SANS) are two key tools to probe the dynamic and static structure factors, respectively, in soft matter. Usually, DLS and SANS measurements are performed separately, in different laboratories, on different samples, and at different times. However, this methodology has particular disadvantages for a large variety of soft materials, which exhibit a high sensitivity to small changes in fundamental parameters, such as waiting times, concentration, pH, and ionic strength. Here, we report on a new portable DLS-SANS apparatus that allows one to simultaneously measure both the microscopic dynamics (through DLS) and the static structure (through SANS) on the same sample. The apparatus has been constructed as a collaboration between two laboratories, each an expert in one of the scattering methods, and was commissioned on the LOQ and ZOOM SANS instruments at the ISIS Pulsed Neutron and Muon Source, U.K.

Determination of effective temperatures of hydrogenated and deuterated alcohols using the VESUVIO spectrometer

We studied the effective temperatures of hydrogen and deuterium in normal 1-propanol, 2-propanol and n-butanol and fully deuterated 2-propanol and n-butanol at the VESUVIO spectrometer (ISIS Pulsed Neutron and Muon Source, Rutherford Appleton Laboratory, UK). We found that the effective temperature of H (D) is about 3.9 (2.9) times higher than room temperature, where the experiments were performed. The results from the present analysis were compared to the results from the standard data treatment available in the MANTID software for DINS data, and to results from Molecular Dynamics simulations. We find that the final results obtained following these independent routes agree within few points per cent. We also provide a detailed discussion on how to handle experimental backgrounds, the need to analyze groups of detectors to increase the signal-to-background ratio, and we suggest a range of scattering angles for which the analysis is more robust.

High count rate pulse shape discrimination algorithms for neutron scattering facilities

The performance of EJ-270, a 6Li loaded pulse shape discriminating plastic scintillator was tested for use in applications with high thermal and epithermal neutron fluxes such as neutron scattering facilities. The short decay time of EJ-270 make it of interest for high count rate applications. To realize this, 4 PSD algorithms were tested. The algorithms were selected based on the potential for high rate applications and simplicity. These algorithms were the charge integration method with and without the addition of a digital low pass filter, a measurement of the time to 10% of peak amplitude and a method we call the “tail sum” which utilizes a digital low pass filter and sums a small number of samples in the tail of each pulse. These algorithms were benchmarked using the figure of merit, the γ-sensitivity and potential rate capability. The charge integration method gave the highest figure of merit of 1.37 using a long window of 272.5 ns but had a γ-sensitivity of 2×10−6 which was poorer than the tail sum algorithm. The tail sum algorithm was able to achieve a figure of merit of 1.36 with a window of 250 ns and a γ-sensitivity on the order of 10−7. Reducing the integration windows to match the fastest algorithm of time to 10% resulted in the tail sum outperforming the other algorithms with a figure of merit of 1.26 and a γ-sensitivity of 6×10−7. The short charge integration method and tail-sum were compared on the EMMA beamline at the ISIS pulsed neutron and muon source. The tails sum demonstrated better separation between the γ-rays and thermal neutron at an incident peak neutron rate of 9.6×105 neutrons per second.

Measurement of neutron total cross sections at the VESUVIO spectrometer

In this article we examine the procedures to determine total cross sections from neutron transmission experiments performed at the time-of-flight spectrometer VESUVIO (ISIS Pulsed Neutron and Muon Source, at the Rutherford Appleton Laboratory, UK). On the one hand we present a newly developed Python-based algorithm, running within the Mantid analysis environment, to obtain neutron total cross sections as a function of the incident neutron energy, employing the information recorded by the transmission monitor. We describe its basic operating principles and parameters, as well as its user interface, which is applied to a specific example of data processing on a set of graphite samples of different manufacturing processes. On the other hand, we discuss a series of features and recent upgrades that make VESUVIO the instrument of choice for accurate and broad-band thermal neutron cross section measurements.

Chemometrics tools for Advanced Spectroscopic Analyses

Any system is described by several variables, often in the form of hidden information, able to describe and explain functional mechanisms for the majority of the processes which can be evaluated analytically only when we consider entire complex datasets. The relationship between those variables is the key to identify and quantify correlations among the parameters describing the data in a strictly model-free manner. In chemometrics one uses mathematical and statistical methods to improve the understanding of chemical information through the correlation of physical parameters or properties to analytical instrument data. This approach is currently used across chemistry, materials science, biology, with a growing impact is the field of spectroscopy. This paper presents the ability of chemometric technique applied to Advanced Spectroscopic Analyses, examples include spectroscopic data collected from both the High- resolution neutron Spectrometer TOSCA, operating at the ISIS pulsed Neutron and Muon Source (UK) and X-ray fluorescence (XRF) spectroscopy. This work demonstrates the high-resolution of the Principal Component Analysis (PCA) to a spectroscopic data-set dealing with the determination of marker bands from Inelastic Neutron Scattering (INS) spectra of a large data- set, the presence of a probably additional transition phase of one globular molecule and evidencing the metallic nature of the black/brownish inscriptions on daily-use textiles used in ancient Egypt. This study will pave the way for the analysis of multi-parametric, high-throughput INS data, now within reach using state-of-the-art chemical neutron spectrometers such as VESPA.

FLUKA simulations and benchmark measurements of the YAP(Ce) scintillators installed on the VESUVIO spectrometer

We present experimental results and FLUKA Monte-Carlo simulations reproducing the counting efficiency and the energy resolution of the cerium-activated yttrium-aluminium-perovskite photon detectors installed on the VESUVIO neutron spectrometer at the ISIS Pulsed Neutron and Muon Source. In particular, we investigate the performance of these detectors in the energy range between 100 keV and 300 keV. In this range, the γ-emission of the 197Au resonant analyser foils, installed on VESUVIO to select the energy of scattered neutrons, is predominant. Such photons are currently discarded by the low-level discrimination threshold of the acquisition electronics set to 600 keV. Here, we model the detector crystals for a series of thickness values, and we discuss how 2-cm-thick crystals would significantly reduce the acquisition times with respect to the 6-mm-thick crystals employed at present. Additionally, we show how the signal-to-background ratio can be substantially enhanced by shielding the scintillators with 0.5-mm-thick Pb foils. We finally discuss the improved detection performance on a model sample of interest for Cultural-Heritage applications.

Cu-based alloys as a benchmark for T-PGAA quantitative analysis at spallation neutron sources

In this paper, we present, for the first time, a quantitative analysis carried out using time-resolved prompt gamma activation analysis (T-PGAA), a technique currently under development at the ISIS pulsed Neutron and Muon Source in Oxfordshire.

Developments towards Bragg edge imaging on the IMAT beamline at the ISIS pulsed neutron and muon source: BEAn software

The BEAn (Bragg Edge Analysis) software has been developed as a toolkit for analysis of Bragg edges and strain maps from data obtained at the time-of-flight imaging instrument IMAT or other compatible instruments. The code is built primarily using Python 3 and the Qt framework, and includes tools useful for neutron imaging such as principal component analysis. This paper introduces BEAn and its features, briefly discuses the scientific concepts behind them, and concludes with planned future work on the code.

Preface

The 12th International Conference on Polarised Neutrons for Condensed Matter Investigations (PNCMI 2018) was held from 3rd-6th July 2018 at Milton Hill near Abingdon, UK. 105 registered participants attended the conference which benefitted from unusually glorious summer weather in the peaceful surroundings of the house. This biennial meeting was inaugurated in Dubna (Russia) in 1996 and since then has been the main forum for condensed matter researchers and polarized neutron instrument scientists to get together to discuss current scientific and technical challenges in the field of polarized neutron scattering, as well as highlighting recent achievements and challenges.The PNCMI 2018 conference programme continued this tradition of providing a broad overview of both cutting edge science enabled by polarised neutron methods and technical developments that push the boundaries of neutron science. Of the many scientific highlights from the conference presented in this volume of proceedings, the paper of Prof. Stephen Lovesey (Rutherford Appleton Laboratory, UK) et al. on the discovery of unusual time- and parity-odd multipoles (anapoles) in a long-studied actinide intermetallic deserves particular mention, as does the fine work of Dr. Stephane Raymond (CEA-Grenoble, France) et al., which shows an unusual cancellation of the magnetic and nuclear intensities in the excitation spectrum of a magnetocaloric material. A particular standout technical achievement is presented in a paper by Dr Stephan Sponar (TU Wien, Austria) and co-workers on the ongoing development of a compact interferometer to study a previously contentious “which-way” measurement of neutron trajectories, highlighting the strength of polarised neutrons as a quantum mechanical probe.PNCMI 2018 was preceded by a polarised neutron summer school on the two days prior to the conference, organised by staff at the ISIS pulsed Neutron and Muon source of the STFC-Rutherford Appleton Laboratory. 15 PhD students attended lectures presented by Prof. Ken Andersen (European Spallation Source, Sweden), Dr. Jörg Voigt (FZ-Jülich, Germany), Dr. Joe Paddison (University of Cambridge, UK) and ISIS polarized neutron instrument scientists. Practical sessions on ISIS instruments included; polarised neutron reflection, 3He spin filters, and polarised single crystal diffraction. One of the great successes of PNCMI 2018 was the large attendance by an international cohort of PhD students and their very impressive contributions to the conference programme. The PhD poster prizes (sponsored by Oxford Instruments, UK) were awarded to Niels Geerits (TU Wien, Austria / TU Delft, Netherlands) presenting a novel time-of-flight-MIEZE spectrometer, and Gesara Bimashofer (Paul Scherrer Institut, Switzerland) for a polarized neutron reflectometry study of lithium-intercalated manganite thin-films. The future of polarized neutron scattering is in very safe and capable hands.The organisers would like to take this opportunity to gratefully acknowledge the support of the international advisory committee and the conference sponsors; ISIS (UK), Oxford Instruments (UK), The Institute of Physics (UK), The European Spallation Source (Sweden), Swiss Neutronics (Switzerland), Ansto (Australia) and the Institut Laue-Langevin (France). Special thanks are due to staff at Milton Hill for their hard work during the conference, and to Claire Garland of the Institute of Physics and her team for their excellent organizational support.The next International Conference on Polarised Neutrons for Condensed Matter Investigations will take place in Maryland in 2020 and will hosted by the NIST Center for Neutron Research (NCNR).Ross Stewart (Conference Chair)Gøran Nilsen (Editor)Rob Dalgliesh (Editor)

Optimization of detection strategies for epithermal neutron spectroscopy using photon-sensitive detectors.

In this work, we discuss an improved detection procedure for the photon-sensitive yttrium-aluminum-perovskite detectors installed on the VESUVIO spectrometer at the ISIS pulsed neutron and muon source. By decreasing the low-level energy threshold of detected photons, we observe an increased count rate up to a factor ∼3, and a decrease of relative error bars and noise of ∼40% and 35%, respectively, for deep inelastic neutron scattering measurements. In addition, we demonstrate how the reported optimization may increase the accuracy in the line shape analysis of neutron Compton profiles, as well as in the application of the mean-force approach to detect the anisotropy and anharmonicity in the single-particle local potential. We envisage that such an upgrade of the detection procedure would have a substantial impact on the VESUVIO scientific programme based on deep inelastic neutron scattering investigations.

Solid State Battery Cells for in Operandi Diffusion Measurements Using µ+sr Spectroscopy

Solid state lithium ion batteries (SSBs) have been widely tipped to revolutionise energy storage technology. The combination of increased safety, longer lifetime, larger electrochemical potential window and higher energy density offered has led to sustained global research into their development. One important aspect of that development is the dynamics of ion diffusion, particularly through the bulk solid electrolyte but also at the electrode/electrolyte interface. Ion diffusion rates can limit how fast batteries can be charged/discharged, with charge movement across the electrode/electrolyte boundary especially key in SSBs, which can experience poor interfacial contact. An increased understanding of microscopic level ion behaviour at these boundaries will prove valuable, but has so far been elusive with techniques such as NMR and impedance spectroscopy yielding inconsistent results.1,2 Muon spin relaxation (µ+SR) spectroscopy is a relatively new technique used to investigate Li+ migration mechanisms, using spin-polarised positive muons created using a synchrotron. The muons can be controlled to stop at any point within a battery, acting as an atomic scale probe of charge movement in a particular area within the crystal structure. This occurs as an implanted muon’s spin is perturbed by the magnetic field of nearby diffusing ions. After an average lifetime of 2.2 µs the muon will decay into a positron, emitted preferentially along the direction of the muon spin at the instant of decay. Detection of the asymmetry of emitted positrons gives a time evolution of the muon ensemble’s spin polarisation, yielding information on ion diffusion dynamics and activation energies. µ+SR has been proven a successful technique to study in situ batteries, producing accurate measurements that are consistent with first-principle calculations.2,3 This research will focus on the study of the promising solid-state battery electrolyte material Al-doped LLZO (Li7La3Zr2O12), using µ+SR spectroscopy as a reliable and reproducible probe. The anode and cathode materials used will be Li4Ti5O12 and LiCoO2 to complete the cell. This cell will be tested in situ from room temperature to around 80ºC on the EMU beamline at ISIS Pulsed Neutron and Muon Source. Any insights gained will be translated back to design principles to optimise battery performance. Power Source, 2014, 268, 153–162Mater. Chem. A, 2017, 5, 8653Mater. Chem. A, 2016, 4, 1729Phys. Scr., 2013, 88, 068509

Validation of a new data-analysis software for multiple-peak analysis of γ spectra at ISIS pulsed Neutron and Muon Source

Abstract In this work, we present a multi-peak fitting code in order to establish a new protocol for the analysis of γ spectra at ISIS pulsed Neutron and Muon Source. The protocol, relying on the ROOT framework developed at CERN, has been tailored for the analysis of two specific gamma emitters – 241Am and 133Ba – and its results have been compared to those generated by Hypermet PC, a dedicated software package specifically devoted to the analysis of neutron induced γ -ray spectra and of widespread use since late 1990s. This new fitting procedure is scheduled for integration into the software for time-resolved prompt-gamma activation analysis, T-PGAA, currently under development at ISIS. T-PGAA allows for the simultaneous acquisition of photon energy and neutron time of flight, respectively, when prompt gamma rays are emitted by a sample after neutron absorption, essentially combining neutron resonance capture analysis (NRCA) and prompt gamma activation analysis (PGAA).

Upgrade to the MAPS neutron time-of-flight chopper spectrometer.

The MAPS direct geometry time-of-flight chopper spectrometer at the ISIS pulsed neutron and muon source has been in operation since 1999, and its novel use of a large array of position-sensitive neutron detectors paved the way for a later generations of chopper spectrometers around the world. Almost two decades of experience of user operations on MAPS, together with lessons learned from the operation of new generation instruments, led to a decision to perform three parallel upgrades to the instrument. These were to replace the primary beamline collimation with supermirror neutron guides, to install a disk chopper, and to modify the geometry of the poisoning in the water moderator viewed by MAPS. Together, these upgrades were expected to increase the neutron flux substantially, to allow more flexible use of repetition rate multiplication and to reduce some sources of background. Here, we report the details of these upgrades and compare the performance of the instrument before and after their installation as well as to Monte Carlo simulations. These illustrate that the instrument is performing in line with, and in some respects in excess of, expectations. It is anticipated that the improvement in performance will have a significant impact on the capabilities of the instrument. A few examples of scientific commissioning are presented to illustrate some of the possibilities.

Muons at ISIS.

For the last 30 years, muon experiments at ISIS pulsed neutron and muon facility at the Rutherford Appleton Laboratory, Oxfordshire have been making a significant contribution to a number of scientific fields. The muon facilities at ISIS consist of eight experimental areas. The European Commission Muon facility consists of three experimental areas with a fixed momentum (28 MeV c-1). The RIKEN-RAL facility has a variable momentum (17-90 MeV c-1) and a choice of negative or positive muons delivering muons to four experimental areas. There is also an area recently used for a muon ionization cooling experiment. In this paper, the ISIS pulsed muon facilities are reviewed, including the beam characteristics that could be useful for muography experiments.This article is part of the Theo Murphy meeting issue 'Cosmic-ray muography'.

Neutron resonance capture analysis and chemometric tools: an integrated approach

A joint approach based on the Neutron Resonance Capture Analysis (NRCA) integrated by chemometric tools namely Principal Component Analysis (PCA) is used to determine the semi-quantitative isotopic composition of a large set of Sumerian pottery. Here, we present NRCA results from the experimental campaign carried out on the INES beamline at the ISIS pulsed neutron and muon source (Rutherford Appleton Laboratory, UK). The potteries come from the archaeological site still under excavation of Abu Tbeirah, a 3rd millennium BCE site located in Southern Iraq, in the S-E periphery of the city of Nasiriyah. NRCA allows to determine the presence and the relative isotopic amounts, while the Principal Component Analysis distinguishes the elements/isotopes linked to the raw materials from the decay products due to contaminants that affect the potteries under investigation.

Data analysis of neutron Compton scattering experiments using MANTID

The VESUVIO spectrometer at the ISIS pulsed neutron and muon source is an epithermal and thermal neutron station requiring a software suite able to tackle the analysis of experimental data from several neutron techniques. We present an update on the tools available within the MANTID environment for the treatment of neutron Compton scattering data, and we discuss new strategies for the analysis of neutron Compton profiles and momentum distributions that provide robustness to the scientific studies based on this technique.