Low Angle Detector Research Articles

A High-Granularity Timing Detector for the ATLAS Phase-II upgrade

The increase of the particle flux at the HL-LHC with instantaneous luminosities up to L=7.5 × 10 34 cm −2 s −1 will have a severe impact on the ATLAS detector reconstruction and trigger performance. The end-cap and forward region where the liquid Argon calorimeter has coarser granularity and the inner tracker has poorer momentum resolution will be particularly affected. A High Granularity Timing Detector will be installed in front of the liquid Argon end-cap calorimeters to help in charged-particle reconstruction and luminosity measurement. This low angle detector is introduced to augment the new all-silicon Inner Tracker in the pseudo-rapidity range from 2.4 to 4.0. Two silicon-sensor double-sided per end-cap will provide precision timing information for minimum-ionizing particles with a resolution as good as 30 ps per track in order to assign each particle to the correct vertex. Readout cells have a size of 1.3 mm × 1.3 mm, leading to a highly granular detector with 3.7 million channels. The Low Gain Avalanche Detectors technology has been chosen as sensor as it provides excellent timing performance. The requirements and overall specifications of the High Granularity Timing Detector are presented as well as the technical design and the project status. The on-going R&D effort carried out to study the sensors, the readout ASIC, and the other components, supported by laboratory and test beam results, are also presented.

Progress in High Resolution Chopper Spectrometer HRC by improving collimator and Fermi chopper

The High Resolution Chopper Spectrometer (HRC) is installed at the Japan Proton Accelerator Research Complex (J-PARC) and is utilized for a wide range of dynamical studies of materials over a wide energy-momentum space with high resolution. Neutron Brillouin scattering (NBS), i.e., inelastic neutron scattering close to the forward direction, can be performed with the HRC, because this instrument utilizes low angle detectors and high-energy neutrons which facilitates a high resolution. Since the solid angle of the detection area for NBS experiments is limited to very low scattering angles, improvements of the HRC are required to increase the neutron flux with reducing the background. Given the success of the HRC for NBS studies, the neutron intensities for NBS experiments have been improved by changing the detector layout, reducing deformation of the slit package during rotation of the Fermi chopper, and fabricating a longer collimator. At present, we have made further improvements. At around the incident neutron energy Ei = 100 meV, the neutron flux was significantly increased for an energy resolution of ΔE∕Ei = 2%, and the best energy resolution achieved was nearly 1% resolution with an acceptable neutron flux.

Comparison of Experiment and Simulation of the triple GEM-Based Fast Neutron Detector**Supported by the National Natural Science Foundation of China under Grant Nos 11135002, 11305232 and 11175076, and the Foundation of China Spallation Neutron Source: Study and Development of the High-performance and Low-angle Detector.

A detector for fast neutrons based on a 10 × 10 cm2 triple gas electron multiplier (GEM) device is developed and tested. A neutron converter, which is a high density polyethylene (HDPE) layer, is combined with the triple GEM detector cathode and placed inside the detector, in the path of the incident neutrons. The detector is tested by obtaining the energy deposition spectrum with an Am Be neutron source in the Institute of Modern Physics (IMP) at Lanzhou. In the present work we report the results of the tests and compare them with those of simulations. The transport of fast neutrons and their interactions with the different materials in the detector are simulated with the GEANT4 code, to understand the experimental results. The detector displays a clear response to the incident fast neutrons. However, an unexpected disagreement in the energy dependence of the response between the simulated and measured spectra is observed. The neutron sources used in our simulation include deuterium-tritium (DT, 14 MeV), deuterium-deuterium (DD, 2.45 MeV), and Am Be sources. The simulation results also show that among the secondary particles generated by the incident neutron, the main contributions to the total energy deposition are from recoil protons induced in hydrogen-rich HDPE or Kapton (GEM material), and activation photons induced by neutron interaction with Ar atoms. Their contributions account for 90% of the total energy deposition. In addition, the dependence of neutron deposited energy spectrum on the composition of the gas mixture is presented.

The extendedQ-range small-angle neutron scattering diffractometer at the SNS

The extendedQ-range small-angle neutron scattering diffractometer (EQ-SANS) at the Spallation Neutron Source (SNS), Oak Ridge, is designed for wide neutron momentum transfer (Q) coverage, high neutron beam intensity and good wavelength resolution. In addition, the design and construction of the instrument aim to achieve a maximum signal-to-noise ratio by minimizing the background. The instrument is located on the high-power target station at the SNS. One of the key components in the primary flight path is the neutron optics, consisting of a curved multichannel beam bender and sections of straight neutron guides. They are optimized to minimize neutron transport loss, thereby maximizing the available flux on the sample. They also enable the avoidance of a direct line of sight to the neutron moderator at downstream locations. The instrument has three bandwidth-limiting choppers. They allow a novel frame-skipping operation, which enables the EQ-SANS diffractometer to achieve a dynamicQrange equivalent to that of a similar machine on a 20 Hz source. The two-dimensional low-angle detector, based on3He tube technologies, offers very high counting rates and counting efficiency. Initial operations have shown that the instrument has achieved its design goals.

The very low angle detector for high-energy inelastic neutron scattering on the VESUVIO spectrometer

The Very Low Angle Detector (VLAD) bank has been installed on the VESUVIO spectrometer at the ISIS spallation neutron source. The new device allows for high-energy inelastic neutron scattering measurements, at energies above 1eV, maintaining the wave vector transfer lower than 10Å-1. This opens a still unexplored region of the kinematical (q,ω) space, enabling new and challenging experimental investigations in condensed matter. This paper describes the main instrumental features of the VLAD device, including instrument design, detector response, and calibration procedure.

Effects of tilt on high-resolution ADF-STEM imaging

A study of the effects of small-angle specimen tilt on high-resolution annular dark field images was carried out for scanning transmission electron microscopes with uncorrected and aberration-corrected probes using multislice simulations. The results indicate that even in the cases of specimen tilts of the order of 1 ∘ a factor of 2 reduction in the contrast of the high-resolution image should be expected. The effect holds for different orientations of the crystal. Calculations also indicate that as the tilted specimen gets thicker the contrast reduction increases. Images simulated with a low-angle annular dark field detector show that tilt effects are more pronounced in this case and suggest that these low-angle detectors can be used to correct specimen tilt during scanning transmission electron microscopes operation.

Investigation of high-energy inelastic neutron scattering from liquid water confined in silica xerogel

High-energy inelastic neutron scattering (HINS) employing epithermal neutrons is a new technique under development at the VESUVIO spectrometer at ISIS, aiming to access the high-energy and low wave-vector transfer region in neutron scattering experiments at eV energies. New neutron detectors have been developed for HINS based on the resonant detector (RD). These make use of the detection of prompt gammas after neutron absorption in an analyzer foil. The RD is used in the very low angle detector (VLAD) bank, which will extend the explored kinematical region to momentum transfer <10 Å −1, whilst still keeping energy transfer >300 meV. The final VLAD will cover the scattering range 1–5° and will be installed by the end of 2005. The results obtained with prototype VLAD detectors on polycrystalline ice and liquid water in silica xerogels provide a demonstration of the feasibility of the measurements under realistic conditions.

VLAD for epithermal neutron scattering experiments at large energy transfers

The Very Low Angle Detector (VLAD) bank will extend the kinematical region covered by today's epithermal neutron scattering experiments to low momentum transfer (<10 Å−1) together with large energy transfer <1 eV. Such kinematical region is so far unexplored and will allow for new experimental studies in condensed matter systems. VLAD is at present being commissioned on the VESUVIO spectrometer at the ISIS pulsed neutron source. It consists of an array of Resonant Detectors covering the scattering range 1°-4°. In this paper the design of VLAD is presented together with Montecarlo simulations of the detector performances. The results of tests made with prototype VLAD detectors are also presented, confirming the usefulness of the Resonance Detector for measurements at very low scattering angles.

The O–H stretching band in ice Ih derived via eV neutron spectroscopy on VESUVIO using the new very low angle detector bank

Strong demand exists for an experimental facility enabling new experimental investigations on condensed matter systems based on epithermal neutron scattering at high energy and low momentum transfers. This need will be met by the very low angle detector (VLAD) bank, to be installed on the VESUVIO spectrometer at the ISIS spallation neutron source. The equipment will operate in the scattering angular range 1°<2θ<5°. Scattering measurements from a polycrystalline ice sample using a VLAD prototype demonstrates the effectiveness of the detection technique adopted for the construction of the full detector array. The resulting density of states in ice is 9±2 atoms/cell, in agreement with previous measurements.

Development of the Very Low Angle Detector (VLAD) for detection of epithermal neutrons at low momentum transfers

New perspectives for epithermal neutron spectroscopy are opened up by the recent development of new instrumentation for inverse geometry time of flight spectrometers at pulsed neutron sources. One example is the Very Low Angle Detector (VLAD) bank which will be installed as an upgrade of the VESUVIO neutron spectrometer, at the ISIS pulsed neutron source. VLAD is developed for detecting epithermal neutrons in the 1-100 eV energy range at very low scattering angles (l°-5°). VLAD will extend the kinematical region covered by today's neutron scattering experiments to the region of low wave vector transfers ( - 1 ) and high energy transfers (>1 eV). Accessing such kinematical region will allow new experimental studies in condensed matter systems. The neutron detection is based on Resonance Detectors (RD), which consist of the combination of a resonance foil used as neutron-to-gamma converter and a photon detector. The results obtained with a prototype VLAD detector confirm the potential of this kind of experiments at scattering angles as low as 2°- 5°. GEANT4 simulations are used to address issues, such as detector cross talk, which arise with the construction of compact RD arrays.

Inelastic Neutron Scattering from CeOs4Sb12

Inelastic Neutron Scattering from CeOs₄Sb₁₂

Development of the very low angle detector for epithermal neutron scattering at low momentum transfers

The design and prototype tests of the Very Low Angle Detector (VLAD) for epithermal neutron scattering at low momentum transfers are presented. The detector will be installed on the VESUVIO spectrometer at the ISIS spallation neutron source for so-called High-energy Inelastic Neutron Scattering (HINS) experiments. It will consist of an array of Resonant Detectors (RD) covering the scattering range 1/spl deg/-5/spl deg/. The results of prototype tests with a reduced set of RD units demonstrate the feasibility of the measurement in the adverse environmental conditions of ISIS. Simulations of particle interactions using the GEANT4 code show that the envisaged detector design can meet the requirements in terms of efficiency, cross-talk between detection channels and neutron scattering events in the detector.

Resolution of the VESUVIO spectrometer for High-energy Inelastic Neutron Scattering experiments

New perspectives for epithermal neutron spectroscopy have been opened up as a result of the development of the Resonance Detector and its use on inverse geometry time-of-flight spectrometers at spallation sources. A special application of the Resonance Detector is the Very Low Angle Detector Bank (VLAD) for the VESUVIO spectrometer at ISIS, operating in the angular range 1 ∘ < 2 θ < 5 ∘ . This equipment allows High-energy Inelastic Neutron Scattering (HINS) measurements to be performed in the ( q , ω ) kinematical region at low wavevector ( q < 10 Å - 1 ) and high energy (unlimited) transfer ℏ ω > 500 meV , a regime so far inaccessible to experimental studies on condensed matter systems. The HINS measurements complement the Deep Inelastic Neutron Scattering (DINS) measurements performed on VESUVIO in the high wavevector q ( 20 Å - 1 < q < 250 Å - 1 ) and high energy transfer ( ℏ ω > 1 eV ) , where the short-time single-particle dynamics can be sampled. This paper will revise the main components of the resolution for HINS measurements of VESUVIO. Instrument performances and examples of applications for neutron scattering processes at high energy and at low wavevector transfer are discussed.

Development of new instrumentation for epithermal neutron scattering at very low angles

New perspectives for epithermal neutron spectroscopy are opened up by the recent developments of Resonance Detectors (RD) for inverse geometry time-of-flight spectrometers at pulsed neutron sources. The RD is based on the combination of an analyser foil used as neutron-to-gamma converter and a suitable photon detector. Here, we report on the state of the RD which is based on a YAP scintillator viewing a natural uranium analyser foil. The response of the YAP detector to the radiative capture γ emission from the uranium analyser foil has been characterized with a bi-parametric measurement of a reference Pb sample, which allowed 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 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 photon energy at about 600 keV. The first application of RD is the Very Low Angle Detector Bank (VLAD) which is planned to be installed in the next three years as an upgrade of the VESUVIO spectrometer, at the ISIS pulsed neutron source. VLAD will extend the ( q, ω) kinematical to low wave vector transfers ( q < 10 Å - 1 ) coupled to high-energy transfers ( ℏ ω > 1 eV ), which is still unexplored by neutron scattering experiments. The first measurements obtained on an ice sample with a VLAD prototype consisting of four RD units are presented here.

The resonant detector and its application to epithermal neutron spectroscopy

New perspectives for epithermal neutron spectroscopy are being opened by the development of the resonant detector (RD) and its use on inverse geometry time of flight spectrometers at spallation sources. The RD was first proposed in the 1980s and was recently brought to a performance level exceeding conventional neutron-sensitive Li-glass scintillator detectors. It features a photon counter coupled to a neutron analyzer foil. Resonant neutron absorption in the foil results in the emission of prompt gamma rays that are detected in the photon counter. The dimensions of the RD set the spatial resolution that can be achieved, ranging from a fraction of a cm to several cm. It can thus be tailored to the construction of detector arrays of different geometry. The main results of the research on this kind of detector are reported leading to the present optimized RD design based on a combination of YAP scintillation photon counter and uranium or gold analyzer foils. This detector has already been selected for application in the upgrade of the VESUVIO spectrometer on ISIS. A special application is the Very Low Angle Detector (VLAD) bank, which will extend the kinematical region for neutron scattering to low momentum transfer (<10 Å −1) whilst still keeping energy transfer >1 eV, thus allowing new experimental studies in condensed matter systems. The first results of tests made with prototype VLAD detectors are presented, confirming the usefulness of the RD for measurements at scattering angles as low as 2–5°.

Recent developments of the e.VERDI project at ISIS

Epithermal neutrons are unique probes for deep inelastic neutron scattering (DINS) at high-energy and high-momentum transfer and inelastic neutron scattering (INS) at high-energy and low-wave vector transfers. In the latter case the kinematic range has recently been revisited given that the high values of initial and final wave vectors achievable in a scattering process coupled to small scattering angles allow to access a so far unexplored region in q, ω, i.e ω>1 eV and q<10 Å −1. In order to exploit DINS and INS in the high-energy and low-momentum range, a very low angle detector (VLAD) bank will be delivered within the e.VERDI Project together with a novel bank at intermediate scattering angles. The former will provide a new tool for investigating high-energy excitations in magnetic systems and semiconductors. The VLAD bank will be constructed following the concept of a resonance detector (RD) spectrometer, recently revised for DINS experiments in the range 1–100 eV.This is a more promising approach in terms of efficiency and signal-to-noise ratio compared to standard neutron counting techniques at eV energies. Results from two devices, cadmium zinc telluride (CZT) solid-state detectors and YAlO 3 perovskite (YAP) scintillators used in RD configurations, will be presented.

Photon detectors for epithermal neutron scattering at high- ω and low- q

Inelastic epithermal neutron scattering at high energy ( ℏω⩾1 eV ) and low wave vector ( q⩽10 A ̊ −1 ) transfers is the unique technique for the investigation of high-energy excitations in a variety of systems, ranging from magnetic materials to semiconductors. The key issue in order to make these measurements feasible on inverse geometry spectrometers, is to develop suitable detection systems for neutrons in the energy range 1–100 eV . The Resonance Detector Spectrometer configuration has to be considered as the most promising approach for electron Volt neutron spectroscopy. This configuration will be employed in the new low angle detector bank, VLAD, planned for VESUVIO spectrometer operating at ISIS source.

Development of resonant detectors for epithermal neutron spectroscopy at pulsed neutron sources

New perspectives for epithermal neutron spectroscopy are opened by the development of new detectors for inverse geometry time of flight spectrometers at pulsed neutron sources. One example is the Very Low Angle Detector (VLAD) bank planned to be delivered, within the next 4 years, within the eVERDI project, on the neutron spectrometer VESUVIO, at the ISIS pulsed neutron source (UK). VLAD will extend the ( q, ω) kinematical region for neutron scattering to low wavefactor transfer ( q<10 Å −1) still keeping energy transfer >1 eV, thus allowing the investigations of new experimental studies in condensed matter systems. The technique being developed for detection of epithermal neutrons, within this low q and high-energy transfer region, is the Resonance Detection Technique. In this work, the state of the detector development will be presented with special focus on the results obtained with some prototype detectors, namely YAP scintillators and cadmium–zinc–telluride semiconductors.

Observation of transverse phonon modes in the first Brillouin zone in aluminum

We describe phonon dispersion measurements on a single crystal of aluminum, using the 1280-pixel low-angle detector on PHAROS at Los Alamos. “Forbidden” transverse phonons are observed in the first Brillouin zone: these are due to multiple scattering that preserves the Q-dependence of the dispersion surface. We discuss the use of large-area detectors for imaging dispersion surfaces.

High-energy spin waves in the linear-chain antiferromagnet KFeS2.

The chopper spectrometer MARI at the ISIS pulsed neutron source was used to measure the spin-wave dispersion in the Heisenberg linear-chain antiferromagnet KFeS 2 at 10.7 K. Aligning the chain axis of a 3.4-cm 3 single crystal with the direction of incidence allowed the signal to be integrated over all low-angle detectors (2θ<≃10 o ) without significant loss of resolution