E. M. Schooneveld

Strain imaging by Bragg edge neutron transmission

The Bragg edges appearing in the transmitted time-of-flight spectra of polycrystalline materials have been recorded using a two-dimensional array of detectors. Subsequent analysis has enabled maps of the elastic strain to be produced.

YAP scintillators for resonant detection of epithermal neutrons at pulsed neutron sources

Recent studies indicate the resonance detector (RD) technique as an interesting approach for neutron spectroscopy in the electron volt energy region. This work summarizes the results of a series of experiments where RD consisting of YAlO3 (YAP) scintillators were used to detect scattered neutrons with energy in the range 1–200 eV. The response of YAP scintillators to radiative capture γ emission from a 238U analyzer foil was characterized in a series of experiments performed on the VESUVIO spectrometer at the ISIS pulsed neutron source. In these experiments a biparametric data acquisition allowed the simultaneous measurements of both neutron time-of-flight and γ pulse height (energy) spectra. The analysis of the γ pulse height and neutron time of flight spectra permitted to identify and distinguish the signal and background components. These measurements showed that a significant improvement in the signal-to-background ratio can be achieved by setting a lower level discrimination on the pulse height at ab...

Neutron resonance spectroscopy for the characterization of materials and objects

The resonance structure in neutron induced reaction cross sections can be used to determine the elemental compositions of materials or objects. The occurrence of resonances is the basis of neutron resonance capture analysis (NRCA) and neutron resonance transmission analysis (NRTA). NRCA and NRTA are fully non-destructive methods to determine the bulk elemental composition without the need of any sample preparation and resulting in a negligible residual activity. They have been applied to determine the elemental composition of archaeological objects and to characterize reference materials used for cross section measurements. For imaging applications a position sensitive neutron detector has been developed within the ANCIENT CHARM project. The detector is based on a 10 × 10 array of 6Li-glass scintillators mounted on a pitch of 2.5 mm, resulting in a 25 × 25 mm2 active area. The detector has been tested at the time-of-flight facility GELINA and used at the ISIS spallation source to study cultural heritage objects.

Single-crystal diamond detector for time-resolved measurements of a pulsed fast-neutron beam

A fast-neutron detector for time-resolved beam measurements at spallation neutron sources is presented. The device features a p-type/intrinsic/metal Schottky barrier structure where the active (intrinsic) detection layer is a 150 μm thick single-crystal diamond obtained by chemical-vapour deposition. Coupling to fast front-end electronics preserves the excellent timing properties of the device as demonstrated in tests performed at the ISIS spallation neutron source in UK. The device represents a novel approach in the field of pulsed fast-neutrons spectroscopic techniques. It will find immediate application in localized (mm resolution) fast-neutron fluence measurements required by neutron irradiation experiments at ISIS also envisaging its use for spectrum measurements.

A resonant detector for high-energy inelastic neutron scattering experiments

Results on the application of the resonant detector (RD) for epithermal neutron scattering in an unexplored kinematical region are presented. The RD is based on resonance radiative neutron capture for energy analysis of the scattered neutrons in an inverse geometry time of flight spectrometer. Application of the RD to detection of epithermal neutrons at very low scattering angles allows access to an unexplored scattering kinematical region, the High-energy Inelastic Neutron Scattering (HINS) region, of low wave vector (3A−1<q<10A−1) and high energy transfers (0.1eV<ω<10eV). Results of HINS measurements from polycrystalline ice are presented.

Fission diamond detectors for fast-neutron ToF spectroscopy

A novel type of fast-neutron (energy En>1 MeV) counter is presented. It is made of a fissionable natural-uranium foil faced to an intrinsic single-crystal diamond that detects the neutron-induced fission fragments escaping the uranium sheet. The fast response of the diamond is a key feature for its use at pulsed spallation neutron sources for applications in beam monitoring and spectrum measurements with mm spatial resolution. This is an important issue to be addressed in the development of beam lines dedicated to the investigation of the so-called single-event effects in electronics, such as the ChipIr instrument designed for the ISIS spallation source in the UK. Tests of the device at the ROTAX beam line at ISIS have shown its potentiality for the proposed application.

DINS measurements on VESUVIO in the Resonance Detector configuration: proton mean kinetic energy in water

Deep Inelastic Neutron Scattering (DINS) measurements have been performed on a liquid water sample at two different temperatures and pressures. The experiments were carried out using the VESUVIO spectrometer at the ISIS spallation neutron source. This experiment represents the first DINS measurement from water using the Resonance Detector configuration, employing yttrium-aluminum-perovskite scintillator and a 238U analyzer foil. The maximum energy of the scattered neutrons was about 70 eV, allowing to access an extended kinematic space with energy and wave vector transfers at the proton recoil peak in the range 1 eV ≤ ω ≤ 20 eV and 25 A−1 ≤ q ≤ 90 A−1, respectively. Comparison with DINS measurements on water performed in the standard Resonance Filter configuration indicates the potential advantages offered by the use of Resonance Detector approach for DINS measurements at forward scattering angles.

Foil cycling technique for the VESUVIO spectrometer operating in the resonance detector configuration

This article reports a novel experimental technique, namely, the foil cycling technique, developed on the VESUVIO spectrometer (ISIS spallation source) operating in the resonance detector configuration. It is shown that with a proper use of two foils of the same neutron absorbing material it is possible, in a double energy analysis process, to narrow the width of the instrumental resolution of a spectrometer operating in the resonance detector configuration and to achieve an effective subtraction of the neutron and gamma backgrounds. Preliminary experimental results, obtained from deep inelastic neutron scattering measurements on lead, zirconium hydride, and deuterium chloride samples, are presented.

A New Position-Sensitive Transmission Detector for Epithermal Neutron Imaging

A new neutron resonant transmission (NRT) detector for epithermal neutron imaging has been designed and built for the ANCIENT CHARM project, which is developing a set of complementary neutron imaging methods for analysis of cultural heritage objects. One of the techniques being exploited is NRT with the aim of performing bulk elemental analysis. The 16-pixel prototype NRT detector consists of independent crystals of 2 × 2 mm pixel size, which allow for 2D position-sensitive transmission measurements with epithermal neutrons. First results obtained at the ISIS pulsed spallation neutron source are presented.

Materials analysis opportunities on the new neutron imaging facility IMAT@ISIS

A new neutron imaging and diffraction facility, called IMAT, is currently being commissioned at the ISIS pulsed neutron spallation source. IMAT will take advantage of neutron time-of-flight measurement techniques for flexible neutron energy selection and effective energy discrimination. The instrument will be completed and commissioned within the next few months, after neutrons have been recently delivered to the sample area. From 2016 IMAT will enable white-beam neutron radiography and tomography as well as energy-dependent neutron imaging. The facility will offer a spatial resolution down to 50 microns for a field of view of up to 400 cm2. IMAT will be operated as a user facility for material science applications and will be open for developments of time-of-flight imaging methods.