arXiv subjects

L. F. Thompson

Publications and source records attributed to L. F. Thompson.

14 recordsLinked to original sources

arXiv2022

Development of Ultra-pure Gadolinium Sulfate for the Super-Kamiokande Gadolinium Project

This paper reports the development and detailed properties of about 13 tons of gadolinium sulfate octahydrate, $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, which has been dissolved into Super-Kamiokande (SK) in the summer of 2020. We evaluate the impact of radioactive impurities in $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ on DSNB searches and solar neutrino observation and confirm the need to reduce radioactive and fluorescent impurities by about three orders of magnitude from commercially available high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$. In order to produce ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, we have developed a method to remove impurities from gadolinium oxide, Gd$_2$O$_3$, consisting of acid dissolution, solvent extraction, and pH control processes, followed by a high-purity sulfation process. All of the produced ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ is assayed by ICP-MS and HPGe detectors to evaluate its quality. Because of the long measurement time of HPGe detectors, we have employed several underground laboratories for making parallel measurements including LSC in Spain, Boulby in the UK, and Kamioka in Japan. In the first half of production, the measured batch purities were found to be consistent with the specifications. However,in the latter half, the $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ contained one order of magnitude more $^{228}$Ra than the budgeted mean contamination. This was correlated with the corresponding characteristics of the raw material Gd$_2$O$_3$, in which an intrinsically large contamination was present. Based on their modest impact on SK physics, they were nevertheless introduced into the detector. To reduce $^{228}$Ra for the next stage of Gd loading to SK, a new process has been successfully establised.

physics.ins-det↗

arXiv2022

A quantitative assessment of Imaging High-Z and Medium-Z materials using Muon Scattering Tomography

Muon Scattering Tomography (MST) has been shown to be a powerful technique for the non-invasive imaging of high-shielded objects. We present here the application of the MST technique to investigate two types of nuclear waste packages, a small-steel drum and a large nuclear waste cask, namely, a CASTOR V/52. We have developed a quantitative method using the contrast-to-noise ratio (CNR) to evaluate the performance of an MST detector system in differentiating between high-, medium-, and low-Z materials inside nuclear waste packages with different shielding types. This study reveals that our MST detector system is able to differentiate between a (10 $\times$ 10 $\times$ 10 cm$^3$) uranium cube, embedded within a concrete matrix inside the small-steel drum, and regions of background signal in six hours of muon exposure time with a CNR value of 3.1$\pm$0.2. During our investigation of the highly-shielded cask, the reconstructed images of the cask contents indicated the ability of our system to detect irregular baskets, such as empty baskets, with a CNR value of 5.0$\pm$0.3 after 30 days of muon exposure. These studies were done using a Monte Carlo simulation tuned to the performance of resistive plate chambers (RPCs) based muon tomography system built by the University of Bristol, which had a reported position resolution of 350 micron. Here we also report the dependence of the performance on the position resolution. We argue that using a combination of RPC and drift chambers (DC) detectors with 700 micron and 4 mm position resolutions respectively is able to generate tomographic images of well-shielded materials in a few hours of muon exposure time. With these position resolutions, our system needs six hours of muon exposure time to produce a good quality image of a cube of uranium with side-length of 10 cm shielded by a concrete matrix with CNR value of 2.4$\pm$0.25.

physics.ins-det↗

arXiv2021

Gadolinium Loaded Cherenkov Detectors for Neutron Monitoring in High Energy Air Showers

Monitoring of high energy cosmic ray neutrons is of particular interest for cosmic ray water Cherenkov detectors as intense bundles of delayed neutrons have been found to arrive after the initial passage of a high energy air shower. In this paper we explore the possibility of building large-area high-energy neutron monitors using gadolinium-loaded Water Cherenkov Detectors (WCDs). GEANT4 simulations of photon production in WCDs are used to estimate the maximum detection efficiency for a hypothetical system. Requiring a series of neutron induced gamma ray flashes distributed over an extended period of time (up to 20μs) was shown to be an effective way to discriminate high energy neutron interactions from other backgrounds. Results suggest that neutron detection efficiencies of 4-15% may be possible using a gadolinium-loaded detection system above 200 MeV. The magnitude of gadolinium loading was also shown to significantly modify the timing response of the simulated detector.

physics.ins-det↗

arXiv2021

Optimising Scintillating Neutron Detectors for Cosmic Ray Soil Moisture Monitoring

Cosmic Ray Neutron Sensing (CRNS) is a powerful technique that allows non-invasive monitoring of soil moisture on length scales well matched for agricultural applications. One factor limiting the use of the technique within industrial agriculture settings is the high initial cost of Helium-3 or BF3 tubes typically used for ground level neutron monitoring. This paper discusses the use of Geant4 to optimise an alternative scintillator based neutron detector that may be applicable for challenges where cost is a higher driving factor than temporal resolution.

physics.ins-det↗

arXiv2021

Material Identification in Nuclear Waste Drums using Muon Scattering Tomography and Multivariate Analysis

The use of muon scattering tomography for the non-invasive characterisation of nuclear waste is well established. We report here on the application of a combination of feature discriminators and multivariate analysis techniques to locate and identify materials in nuclear waste drums. After successful training and optimisation of the algorithms they are then tested on a range of material configurations to assess the system's performance and limitations. The system is able to correctly identify uranium, iron and lead objects on a ~few \text{cm} scale. The system's sensitivity to small uranium objects is also established as $0.90^{+0.07}_{-0.12}$, with a false positive rate of $0.12^{+0.12}_{-0.07}$.

physics.ins-det↗

arXiv2020

3D Printing Neutron Detectors using Scintillating BN/ZnS Resin

In this paper we demonstrate that it is possible to produce low cost neutron-sensitive detectors using stereo-lithography additive manufacturing. A curable scintillating resin is made by mixing BN:ZnS with a commercially available UV resin. This resin is used to print several small area neutron detectors made of arrays of BN:ZnS cones that can be directly coupled to a photo-multiplier tube.

physics.ins-det↗

arXiv2020

Design and performance of a 35-ton liquid argon time projection chamber as a prototype for future very large detectors

Liquid argon time projection chamber technology is an attractive choice for large neutrino detectors, as it provides a high-resolution active target and it is expected to be scalable to very large masses. Consequently, it has been chosen as the technology for the first module of the DUNE far detector. However, the fiducial mass required for "far detectors" of the next generation of neutrino oscillation experiments far exceeds what has been demonstrated so far. Scaling to this larger mass, as well as the requirement for underground construction places a number of additional constraints on the design. A prototype 35-ton cryostat was built at Fermi National Acccelerator Laboratory to test the functionality of the components foreseen to be used in a very large far detector. The Phase I run, completed in early 2014, demonstrated that liquid argon could be maintained at sufficient purity in a membrane cryostat. A time projection chamber was installed for the Phase II run, which collected data in February and March of 2016. The Phase II run was a test of the modular anode plane assemblies with wrapped wires, cold readout electronics, and integrated photon detection systems. While the details of the design do not match exactly those chosen for the DUNE far detector, the 35-ton TPC prototype is a demonstration of the functionality of the basic components. Measurements are performed using the Phase II data to extract signal and noise characteristics and to align the detector components. A measurement of the electron lifetime is presented, and a novel technique for measuring a track's position based on pulse properties is described.

physics.ins-det↗

arXiv2019

Directionally Accelerated Detection of an Unknown Second Reactor with Antineutrinos for Mid-Field Nonproliferation Monitoring

When monitoring a reactor site for nuclear nonproliferation purposes, the presence of an unknown or hidden nuclear reactor could be obscured by the activities of a known reactor of much greater power nearby. Thus when monitoring reactor activities by the observation of antineutrino emissions, one must discriminate known background reactor fluxes from possible unknown reactor signals under investigation. To quantify this discrimination, we find the confidence to reject the (null) hypothesis of a single proximal reactor, by exploiting directional antineutrino signals in the presence of a second, unknown reactor. In particular, we simulate the inverse beta decay (IBD) response of a detector filled with a 1 kT fiducial mass of Gadolinium-doped liquid scintillator in mineral oil. We base the detector geometry on that of WATCHMAN, an upcoming antineutrino monitoring experiment soon to be deployed at the Boulby mine in the United Kingdom whose design and deployment will be detailed in a forthcoming white paper. From this simulation, we construct an analytical model of the IBD event distribution for the case of one $4\mathrm{\ GWt}\pm2\%$ reactor 25 km away from the detector site, and for an additional, unknown, 35 MWt reactor 3 to 5 km away. The effects of natural-background rejection cuts are approximated. Applying the model, we predict $3σ$ confidence to detect the presence of an unknown reactor within five weeks, at standoffs of 3 km or nearer. For more distant unknown reactors, the $3σ$ detection time increases significantly. However, the relative significance of directional sensitivity also increases, providing up to an eight week speedup to detect an unknown reactor at 5 km away. Therefore, directionally sensitive antineutrino monitoring can accelerate the mid-field detection of unknown reactors whose operation might otherwise be masked by more powerful reactors in the vicinity.

physics.ins-det↗

arXiv2019

The application of muon tomography to the imaging of railway tunnels

Cosmic Ray Muon Radiography utilizes highly-penetrating cosmic ray muons to image the density profile of an object of interest. Here we report on the first trial to use a portable field-deployable cosmic ray tracking system in order to image the whole overburden of a UK railway tunnel with short duration scans (c. 30 minutes). A unknown overburden void was identified and, post-trial, confirmed by railway authorities. These experiments demonstrate the identification of hidden construction shafts with high levels of statistical significance as density anomalies within the data.

physics.ins-det↗

arXiv2018

Photon detector system timing performance in the DUNE 35-ton prototype liquid argon time projection chamber

The 35-ton prototype for the Deep Underground Neutrino Experiment far detector was a single-phase liquid argon time projection chamber with an integrated photon detector system, all situated inside a membrane cryostat. The detector took cosmic-ray data for six weeks during the period of February 1, 2016 to March 12, 2016. The performance of the photon detection system was checked with these data. An installed photon detector was demonstrated to measure the arrival times of cosmic-ray muons with a resolution better than 32 ns, limited by the timing of the trigger system. A measurement of the timing resolution using closely-spaced calibration pulses yielded a resolution of 15 ns for pulses at a level of 6 photo-electrons. Scintillation light from cosmic-ray muons was observed to be attenuated with increasing distance with a characteristic length of $155 \pm 28$ cm.

physics.ins-det↗

arXiv2015

Simulation of muon radiography for monitoring CO$_2$ stored in a geological reservoir

Current methods of monitoring subsurface CO$_2$, such as repeat seismic surveys, are episodic and require highly skilled personnel to acquire the data. Simulations based on simplified models have previously shown that muon radiography could be automated to continuously monitor CO$_2$ injection and migration, in addition to reducing the overall cost of monitoring. In this paper, we present a simulation of the monitoring of CO$_2$ plume evolution in a geological reservoir using muon radiography. The stratigraphy in the vicinity of a nominal test facility is modelled using geological data, and a numerical fluid flow model is used to describe the time evolution of the CO$_2$ plume. A planar detection region with a surface area of 1000 m$^2$ is considered, at a vertical depth of 776 m below the seabed. We find that one year of constant CO$_2$ injection leads to changes in the column density of $\lesssim 1\%$, and that the CO$_2$ plume is already resolvable with an exposure time of less than 50 days.

physics.geo-ph↗

arXiv2013

The Electromagnetic Calorimeter for the T2K Near Detector ND280

The T2K experiment studies oscillations of an off-axis muon neutrino beam between the J-PARC accelerator complex and the Super-Kamiokande detector. Special emphasis is placed on measuring the mixing angle theta_13 by observing electron neutrino appearance via the sub-dominant muon neutrino to electron neutrino oscillation, and searching for CP violation in the lepton sector. The experiment includes a sophisticated, off-axis, near detector, the ND280, situated 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to understand better neutrino interactions at the energy scale below a few GeV. The data collected with the ND280 are used to study charged- and neutral-current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. A key element of the near detector is the ND280 electromagnetic calorimeter (ECal), consisting of active scintillator bars sandwiched between lead sheets and read outwith multi-pixel photon counters (MPPCs). The ECal is vital to the reconstruction of neutral particles, and the identification of charged particle species. The ECal surrounds the Pi-0 detector (P0D) and the tracking region of the ND280, and is enclosed in the former UA1/NOMAD dipole magnet. This paper describes the design, construction and assembly of the ECal, as well as the materials from which it is composed. The electronic and data acquisition (DAQ) systems are discussed, and performance of the ECal modules, as deduced from measurements with particle beams, cosmic rays, the calibration system, and T2K data, is described.

physics.ins-det↗

arXiv2011

Characterization and Simulation of the Response of Multi Pixel Photon Counters to Low Light Levels

The calorimeter, range detector and active target elements of the T2K near detectors rely on the Hamamatsu Photonics Multi-Pixel Photon Counters (MPPCs) to detect scintillation light produced by charged particles. Detailed measurements of the MPPC gain, afterpulsing, crosstalk, dark noise, and photon detection efficiency for low light levels are reported. In order to account for the impact of the MPPC behavior on T2K physics observables, a simulation program has been developed based on these measurements. The simulation is used to predict the energy resolution of the detector.

physics.ins-det↗

arXiv2000

Energy calibration of large underwater detectors using stopping muons

We propose to use stopping cosmic-ray muons in the energy calibration of planned and deployed large underwater detectors. The method is based on the proportionality between the incident muon energy and the length of the muon path before it stops. Simultaneous measurements of the muon path and the amplitude of the signal from the photomultiplier tubes allow a relation between the energy deposited in the sensitive volume of the detector and the observed signal to be derived, and also provide a test of detector simulations. We describe the proposed method and present the results of simulations.

hep-ex↗