ISIS Neutron Research Articles

Non-invasive detection of hazardous materials with a thermal-to-epithermal neutron station: a feasibility study towards practical application

The growing scale of the devastation that even a single terrorist attack can cause requires more effective methods for the detection of hazardous materials. In particular, there are no solutions for effectively monitoring threats at sea, both for the off-shore infrastructure and ports. Currently, state-of-the-art detection methods determine the density distribution and the shapes of tested subjects but only allow for a limited degree of substance identification. This work aims to present a feasibility study of the possible usage of several methods available on the thermal-to-epithermal neutron station, VESUVIO, at the ISIS neutron and muon spallation source, UK, for the detection of hazardous materials. To this end, we present the results of a series of experiments performed concurrently employing neutron transmission and Compton scattering using melamine, a commonly used explosive surrogate, in order to determine its signal characteristics and limits of detection and quantitation. The experiments are supported by first-principles modelling, providing detailed scrutiny of the material structure and the nuclear dynamics behind the neutron scattering observables.

The muon beam monitor for the FAMU experiment: design, simulation, test, and operation

FAMU is an INFN-led muonic atom physics experiment based at the RIKEN-RAL muon facility at the ISIS Neutron and Muon Source (United Kingdom). The aim of FAMU is to measure the hyperfine splitting in muonic hydrogen to determine the value of the proton Zemach radius with an accuracy better than 1%. The experiment has a scintillating-fibre hodoscope for beam monitoring and data normalisation. In order to carry out muon flux estimation, low-rate measurements were performed to extract the single-muon average deposited charge. Then, detector simulation in Geant4 and FLUKA allowed a thorough understanding of the single-muon response function, which is crucial for determining the muon flux. This work presents the design features of the FAMU beam monitor, along with the simulation and absolute calibration measurements in order to enable flux determination and enable data normalisation.

Mapping the elemental distribution in archaeological findings through advanced Neutron Resonance Transmission Imaging

This work highlights recent application of energy-selective neutron imaging at the ISIS Neutron and Muon Source, specifically focusing on the development of Neutron Resonance Transmission Imaging (NRTI) at the INES instrument. NRTI is a nuclear technique based on resonant neutron absorption reaction, which combines the sensitivity to elemental and isotopic composition with detailed morphological information, using the epithermal portion of the neutron flux available on the INES instrument at the ISIS facility. Unlike standard neutron radiography and tomography methods, NRTI preserves detailed time and energy information for each detector pixel, enabling enhanced visualisation of elemental distribution inside an object’s volume, with the potential for quantitative elemental analysis. These features combined with the non-destructiveness of NRTI make the method promising for applications in the field of Cultural Heritage, especially when it is employed in a multi-technique approach to provide complementary information about the composition and the crystalline structure of archaeological artefacts. A study related to Heritage Science is presented to demonstrate the effectiveness of NRTI in non-destructive investigations of inhomogeneous artefacts, specifically focusing on the excavation finds related to the first evidence of ancient brass production in Milan, Italy, during Roman times.

Embracing neurodiversity in neutron science

Adam Berlie is a muon instrument scientist at the ISIS Neutron and Muon Source in the UK, having done postdocs in China and Australia. He talks about his career so far, what it’s like to be a neurodivergent researcher, and his role as chair of the UKRI Disability Matters network.

Nanocomposite materials as observed by mass-selective neutron spectroscopy

Abstract This work provides a current, critical view of the application of MAss-selective Neutron SpEctroscopy (MANSE) to nanocomposite materials. MANSE is a unique technique made possible owing to the existence of the pulsed neutron sources. At present, the only operating MANSE spectrometer in the world, VESUVIO, is located at the ISIS Neutron and Muon Source in the UK. We start by providing a brief description of the neutron Compton scattering, the anatomy of a mass-selective neutron spectrometer, and the experimental data treatment. We continue by briefly outlining the main quantum mechanical concepts, models and approximations relevant both to the ab initio prediction and experimental measurement of main MANSE observables. Next, we present several recent exemplars chosen to highlight the use of MANSE in the field of nanocomposites. Our examples include, in chronological order, encapsulated nanoparticles in amorphous silica gel, bioactive glass-ionomer cement, Cu-Ti-C composites, and sodium carboxymethyl starch-based binders in the presence of a mineral matrix. We close by providing our view of the ongoing and future challenges and opportunities in the mass-selective neutron investigation of NQEs in nanocomposite materials.

The Implementation of MuDirac in Geant4: A Preliminary Approach to the Improvement of the Simulation of the Muonic Atom Cascade Process

Muonic Atom X-ray Emission spectroscopy (µ-XES) is a novel elemental technique that exploits the high-energy X-rays emitted from the muonic atom cascade process to characterize materials. At the ISIS Neutron and Muon Source, the technique is performed at Port4 of the RIKEN-RAL facility, with a user demand that is increasing every year. To cope with this demand, it is necessary to continue to improve the method, either for the hardware (detectors, acquisition, etc.) or software (data analysis and interpretation). In both cases, Monte Carlo codes play an important role: with a simulation, it is possible to reproduce the experimental setup and provide a reliable quantitative analysis. In this work, we investigate the capabilities of GEANT4 for such applications. From the results, we observed that the generation of X-rays, especially the kα and kβ transition for high Z atoms, are not in agreement with the experimental ones. A solution to this issue, other than an attempt with a small modification of the GEANT4 cascade class, could be provided by a database of transition energy calculated by a Dirac equation software called MuDirac. The software, developed by the UKRI scientific computing department and the ISIS muon group, can compute all the transition energy for a given nuclide. Here, preliminary results of the implementation of the MuDirac database in GEANT4 are reported.

How can Neutron Imaging contribute to Heritage Science? An overview at the ISIS Neutron and Muon Source

Heritage Science HS spans a large variety of objects and materials, as well as anything that has historic, artistic, anthropological, and natural significance. This paper aims to bridge the gap between the physical and natural sciences and the humanities, and divulge neutron imaging techniques to a wider community. Here we give an introduction of the neutron imaging capabilities at the ISIS Neutron and Muon Source (UK), and a brief overview of some research activities in HS carried out at the facility in recent years, from neutron tomography to elemental imaging.

CO2-mineralization and carbonation reactor rig: Design and validation for in situ neutron scattering experiments-Engineering and lessons learned.

CO2 mineralization via aqueous Mg/Ca/Na-carbonate (MgCO3/CaCO3/Na2CO3) formation represents a huge opportunity for the utilization of captured CO2. However, large-scale mineralization is hindered by slow kinetics due to the highly hydrated character of the cations in aqueous solutions (Mg2+ in particular). Reaction conditions can be optimized to accelerate carbonation kinetics, for example, by the inclusion of additives that promote competitive dehydration of Mg2+ and subsequent agglomeration, nucleation, and crystallization. For tracking mineralization and these reaction steps, neutron scattering presents unprecedented advantages over traditional techniques for time-resolved in situ measurements. However, a setup providing continuous solution circulation to ensure reactant system homogeneity for industrially relevant CO2-mineralization is currently not available for use on neutron beamlines. We, therefore, undertook the design, construction, testing and implementation of such a self-contained reactor rig for use on selected neutron beamlines at the ISIS Neutron and Muon Source (Harwell, UK). The design ensured robust attachment via suspension from the covering Tomkinson flange to stabilize the reactor assembly and all fittings (~25 kg), as well as facilitating precise alignment of the entire reactor and sample (test) cell with respect to beam dimension and direction. The assembly successfully accomplished the principal tasks of providing a continuous flow of the reaction mixture (~500 mL) for homogeneity, quantitative control of CO2 flux into the mixture, and temperature and pressure regulation throughout the reaction and measurements. The design is discussed, with emphasis placed on the reactor, including its geometry, components, and all technical specifications. Descriptions of the off-beamline bench tests, safety, and functionality, as well as the installation on beamlines and trial experimental procedure, are provided, together with representative raw neutron scattering results.

The Vittoria Alata from Brescia: a combined neutron techniques and SEM-EDS approach to the study of the alloy of a bronze Roman statue

The “Vittoria Alata” (Winged Victory) from Brescia, dated around the 1st Century BCE, is one of the most well-known Roman bronzes discovered in Italy. The statue has recently undergone a restoration coordinated by the Opificio delle Pietre Dure di Firenze (OPD) that offered a unique opportunity for a thorough investigation on its manufacturing methods and previous non-documented repair/restauration interventions. In this paper, we present the results of the study of the metal alloy, obtained by neutron techniques and Scanning Electron Microscope analysis (SEM-EDS), on 24 samples of mm-size from various parts of the statue and on a cm-size feather fragment, believed to have detached from the right wing. Time of Flight Neutron Diffraction (ToF-ND) and Neutron Imaging (NI) measurements were performed at the ISIS neutron and muon source, Rutherford Appleton Laboratory, UK; SEM-EDS analysis were carried out at the OPD Scientific Laboratory, Florence, IT. The representativeness of ToF-ND on millimetric samples was confirmed by comparing the results obtained on several large, irradiated areas (few cm2) of an entire bronze frame fragment from the same excavation context with the ones on a millimetric sample taken from the same frame. This investigation led to the characterization of the alloys used for the different parts of the statue and to identify meaningful details on the manufacturing method.

Study of the effective temperatures of two neutron moderating materials: Ethane and triphenylmethane

We studied the effective temperatures of hydrogen and carbon in solid ethane at 80 K and triphenylmethane at 22 K at the VESUVIO spectrometer (ISIS Neutron and Muon Source, Rutherford Appleton Laboratory, UK), using the Deep Inelastic Neutron Scattering (DINS) and Neutron Transmission techniques. The systems are of potential application as moderators for the design of cold neutron sources. We discuss in detail the process of data analysis and parameter fitting, in which we introduced improved algorithms. The results were compared with density functional theory calculations, which yield compatible results. The importance of these determinations for their applications to Nuclear Engineering calculations is highlighted. The results of the effective temperatures obtained are supported by comparisons with the total cross sections measured simultaneously with DINS in this experiment.

Analysis of a neutron-induced conversion electron spectrum of gadolinium

A 100-nm-thick gadolinium layer deposited on a pixelated silicon sensor was activated in a neutron field to measure the internal conversion electron (ICE) spectrum generated by neutron capture products of 155Gd and 157Gd. The experiment was performed at the ISIS neutron and muon facility, using a bespoke version of the HEXITEC spectroscopic imaging camera. Signals originating from internal conversion electrons, Auger electrons, x rays and gamma rays up to 150 keV were identified. The ICE spectrum has an energy resolution of 1.8–1.9 keV at 72 keV and shows peaks from the K, L, M, N+ ICEs of the 79.51 keV and 88.967 keV 2+-0+ gamma transitions from the first excited states in 158Gd and 156Gd, respectively, as well as the K ICEs of the 4+-2+ transitions at 181.931 keV and 199.213 keV from the respective second excited states. Spectrum analysis was performed using a convolution of a Gaussian with exponential functions at the low and high energy side as the peak shaping function. Relative ICE intensities were derived from the fitted peak areas and compared with internal conversion coefficient (ICC) values calculated from the BrIcc database. Relative to the dominant L shell contribution, the K ICE intensity conforms to BrIcc and the M, N, O+ ICE intensities are somewhat higher than expected.

Material limits: the biggest challenges hindering clean hydrogen

The key to unlocking hydrogen's net-zero potential is finding better materials to produce, use and store H2. Professor Martin Owen Jones from ISIS Neutron and Muon Source pinpoints the latest research advances in this area.

Modelling of The New Engineering Diffractometer eMAP at ISIS Target Station 2

eMAP is a new proposed high flux medium-resolution time-of-flight engineering diffractometer that will be built at ISIS Target Station 2. Monte Carlo simulations were performed to optimise the neutron guide to maximise brilliance transfer. eMAP features great flexibility in tuning for flux or resolution. The diffractometer achieves a figure of merit that surpasses the ENGIN-X diffractometer at ISIS by more than a factor 10. The new instrument will bring additional capacity and advanced stress measurement capabilities to the engineering diffraction user programme at the ISIS Neutron and Muon Source.

Overview of planned upgrade to the secondary spectrometer of TOSCA

We describe a proposed upgrade to the indirect-geometry broad-band chemical spectrometer TOSCA at the ISIS Neutron and Muon Source, UK. By replacing the secondary spectrometer of the instrument, we expect a gain in detected intensity of an order of magnitude, improved spectral resolution over the entire energy range of the instrument and an improved signal-to-noise ratio. The new secondary spectrometer consists of 14 analyser modules, each constituted of a large, curved pyrolytic graphite analyser, a beryllium filter and a position-sensitive detector system. We present the prospective design and expected performance of the new analyser module as calculated from ray-tracing simulations. The improved performance will develop the instrument capabilities to tackle new and challenging experiments and ensure that TOSCA remains highly competitive in the years to come.

On the spectral resolution of the broad-band indirect-geometry time-of-flight neutron spectrometer TOSCA

We present a detailed description of the spectral resolution of the TOSCA spectrometer at the ISIS Neutron and Muon Source. We compare an analytical model of the resolution, a numerical model based on ray-tracing simulations and experimental data derived from measurements of the 2,5-diiodothiophene standard. The analytical description is derived by error propagation on the energy transfer equation and accurately accounts for the dimensions of each of the component of the instrument and their neutron scattering or absorption depth-profiles. We obtain excellent agreement between the analytical and numerical descriptions for the ideal time-focusing geometry of TOSCA and also between the simulations of a more realistic model of the instrument and the experimental data. This study provides several insights into the critical contributions to the instrument performance that are directly useful for the proposed upgrade of TOSCA, but also relevant for other broad-band crystal-analyser spectrometers.

SHERPA: A Spectrometer with High Energy Resolution and Polarisation Analysis

SHERPA is a proposed quasielastic neutron spectrometer with polarisation analysis, intended to replace the ageing Iris instrument at the ISIS neutron and muon source. In this paper we present a concept of the instrument along with Monte-Carlo simulations and analysis of possible instrument location. We expect greatly increased count rate compared to Iris (expected from 49 to 660 × Iris) in unpolarised mode and dedicated polarisation analysis capabilities at a more modest count rate increase (~5-70 × Iris). This huge gain in the count rate would be achieved from the combination of three factors: modern neutron guide with high-m coating, and prismatic effect and larger solid angle coverage at the energy analyser. Such an instrument would be the first of its kind and has incredible potential to revolutionise quasielastic neutron scattering technique through the separation of the coherent and incoherent scattering contributions.

Response of nuclear track detector CR-39 to low energy muons

The effectiveness of the PolyAllyl Diglycol Carbonate (PADC) etched solid state nuclear track detector (SSNTD), commonly known as CR-39, as a muon detector is assessed. CR-39 is successfully used to detect higher rest mass particles such as neutrons and protons, and is, for example, widely used in neutron dosimetry applications. CR-39 is generally accepted as being less suitable to detect lower rest mass particles such as muons, and especially electrons, due mostly to their reduced momenta and consequently, reduced stopping power. However, there has been some evidence that CR-39 may have application in the detection of cosmic ray muons. Monte Carlo simulations indicate that CR-39 can detect muons with energies up to 2.8 MeV. Experimental data to demonstrate the ability of CR-39 to detect muons was acquired using the MuSR spectrometer station at the ISIS Neutron and Muon Source. Pits deposited in CR-39 generated by positive muons from the beamline have been characterised and compared with pits deposited by protons and neutrons from other sources. The extent to which a CR-39 SSNTD can discriminate muons from particles with different momenta and rest masses is discussed.

Progress in neutron techniques: towards improved polymer electrolyte membranes for energy devices

Design and implementation of advanced membrane formulations for selective transport of ions and molecular species are critical for creating the next generations of fuel cells and separation devices. It is necessary to understand the detailed transport mechanisms over time- and length-scales relevant to the device operation, both in laboratory models and in working systems under realistic operational conditions. Neutron scattering techniques including quasi-elastic neutron scattering, reflectivity and imaging are implemented at beamline stations at reactor and spallation source facilities worldwide. With the advent of new and improved instrument design, detector methodology, source characteristics and data analysis protocols, these neutron scattering techniques are emerging as a primary tool for research to design, evaluate and implement advanced membrane technologies for fuel cell and separation devices. Here we describe these techniques and their development and implementation at the ILL reactor source (Institut Laue-Langevin, Grenoble, France) and ISIS Neutron and Muon Spallation source (Harwell Science and Technology Campus, UK) as examples. We also mention similar developments under way at other facilities worldwide, and describe approaches such as combining optical with neutron Raman scattering and x-ray absorption with neutron imaging and tomography, and carrying out such experiments in specialised fuel cells designed to mimic as closely possible actual operando conditions. These experiments and research projects will play a key role in enabling and testing new membrane formulations for efficient and sustainable energy production/conversion and separations technologies.

First Tests of a New Facility for Device-Level, Board-Level and System-Level Neutron Irradiation of Microelectronics

The very limited availability of fast neutron facilities, particularly in Europe, for testing of microelectronics has motivated the construction of ChipIr, a new beamline at the ISIS neutron and muon source in the UK. ChipIr has been designed for Single Event Effect testing at the device-level, board-level and system-level which requires a beam of uniform intensity over a selectable area in the order of hundreds of cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Measurements of the beam uniformity are presented in this paper. A memory chip of interest for space applications, based on SRAMs and developed by ESA for monitoring of radiation fields, has been used for a comparative characterization of the beam. Consistent results have been found, giving confidence on the intensity and shape of the fast neutron spectrum of ChipIr.

Observing Formation of the Solid Electrolyte Interface By Operando Neutron Reflectivity

To realise the widespread implementation of future generations of lithium ion batteries (LIBs) in electric vehicles, significant improvements in the lifetime and power density are required. One of the most important aspects in achieving a long battery lifetime is the formation of an effective solid electrolyte interphase (SEI) layer on the anode. This layer forms mostly within the first few charge/discharge cycles by the decomposition of electrolyte components at the electrode/electrolyte interface. Although the importance of the SEI is well accepted, much dispute remains regarding its chemical composition, thickness, morphology and formation/decomposition mechanisms. This is largely due to a lack of characterisation techniques that can accurately probe the electrode-electrolyte interface with nm-scale surface sensitivity under realistic cycling conditions. As a result, most efforts to characterise the SEI have involved ex situ samples, the preparation of which may alter the SEI layer composition. Therefore, in order to gain the most accurate information, there has been a great drive to perform in situ and operando measurements.Neutron techniques offer several advantages for characterising the processes occurring in LIBs, particularly as the negative scattering length of Lithium gives a high sensitivity to changes in the lithium environment, which is not the case with X-ray techniques. Neutron reflectometry (NR) is one of the few techniques with which the nm-scale structure of buried electrode-electrolyte interfaces in a cell can be observed during electrochemical cycling.1 A number of previous studies have investigated thin film silicon or carbon electrodes, but these have typically been carried out across a limited potential range due to concerns about restructuring due to significant lithiation that could otherwise hinder interpretation of the neutron reflectivity data.2-4 To overcome this limitation we have recently used a nickel working electrode (anode) which, given its zero capacity for lithium insertion, does not alter in structure during electrochemical cycling. Here we directly observe the growth of the SEI layer on a nickel anode as a function of potential (2.00-0.05 V) during the first cycle by using our operando cell developed at ISIS Neutron and Muon Source. During the first lithiation cycle (decreasing potential), we observe the growth of a lithium-rich layer directly in contact with the nickel and another, more organic, layer on top of this lithium-rich layer. We are able to track the evolution of these layers with potential, and characterise their chemical composition using additional X-ray Photoelectron Spectroscopy measurements performed on both cycled nickel and commercial graphite electrodes for comparison.