Methodologies for imaging a used nuclear fuel dry storage cask with cosmic ray muon computed tomography

Muons interact with matter via two major interaction mechanisms: ionization and radioactive process, and multiple Coulomb scattering leading to energy loss and trajectory deflection, respectively. For a monoenergetic muon beam crossing an object, the scattering angle follows a Gaussian distribution with a zero mean value and a variance that depends on the atomic number of the material object it traversed. Thus, the measured scattering angle may be used to reconstruct the geometrical and material information of the contents inside the dry storage cask. In traditional X-ray computed tomography, the projection information used to reconstruct the attenuation map of the imaged objects is the negative natural logarithm of the transmission rate of the X-rays, which is equal to the linear summation of the X-ray attenuation coefficients along the incident path. Similarly, the variance of the muon scattering angle is also the linear integral of the scattering density of the objects crossed by the muons. Thus, a muon CT image can be built by equating scattering density with attenuation coefficient. However, muon CT faces some unique challenges including: 1) long measurement times due to low cosmic muon flux, 2) insufficiently accurate muon path models, and 3) the inability to precisely measuring muon momentum. In this work, three different muon path models, two different projection methods, and two different reconstruction methods were investigated for use in muon CT of dry storage casks. The investigation was conducted in a validated Geant4 workspace, both in an ideal case and with relevant engineering restrictions considered. The results of these investigations and the expected benefits for fuel cask monitoring are reported herein

Muon tomography effectiveness in detecting orphan sources in scrap metal

The detection of sealed orphan sources inside scrap metal transportation is a crucial concern for the steel industry, because an accidental melting of radioactive material can produce severe environmental harm. The technique of muon tomography appears to be suitable for this purpose, because it allows to discriminate high-Z materials, measuring multiple scattering of cosmic ray muons crossing the cargo. A European project (RFSR-CT-2010-000033) to exploit this technique started in 2010 and finished in 2012. The aim of the project was to design an inspection portal able to detect lead-shielded radioactive sources hidden in scrap metal containers using cosmic rays. The reconstruction algorithms and their performances were studied in a full simulated environment

Müoni kvantitatiivsed ja kvalitatiivsed uuringud hajuv tomograafia GEANT4 simulatsioonide kaudu: arvutuslik uuring

Müüontomograafia on suhteliselt uudne kuvatehnika, mis kasutab kosmiliste kiirte vastastikmõjus atmosfääriga tekkivat vaba looduslikku müüonite kiirgusvoogu. Müüonite hajumisel põhinevas tomograafias mõõdetakse müüonite levikut ja hajumist uuritavas ruumalas või kehas, mis sõltub peamiselt aine aatomarvust, materjali tihedusest ning paksusest. Käesoleva doktoritöö eesmärk on karakteriseerida müüonite käitumist valitud tomograafilises süsteemis ja materjalides, nagu näiteks tuumamaterjalid. Uuringud on läbi viidud nii kvantitatiivses kui ka kvalitatiivses vormingus. Esiteks, hindasime sissetulevate müüonite kineetilist energiat, kasutades polüvinüültolueenist valmistatud detektorikihtide poolt tekitatavaid müüonite trajektooride hälbeid. Teiseks, hindasime keha positsioneerimise teostatavust triangulatsioonkorrelatsiooni meetodil ning määrasime homogeniseeritud ja homogeniseerimata tuumajäätmete konteinerite mõõtmise jaoks sellised iseloomulikud parameetrid, nagu hajumisjaotus, müüoni neeldumine ja müüonite trajektooride nihked. Püüdsime täiustada ka müüoniallikaid. Selle asemel, et kasutada diskreetse või ühtlase energiajaotusega laiapindset vertikaalset müüonkiirgusallikat, lõime ise keerulisemad, piiratud ulatusega, diskreetse energiaspektriga allikad.Muon tomography is a relatively novel imaging technique that makes use of the free natural flux of muons originating from the interaction of cosmic rays in the atmosphere. The principle behind the muon scattering tomography is to track the propagation of the cosmic ray muons within the target volume through which the incoming muons of a certain energy deviate from their initial trajectories after a series of physical processes predominantly depending on the atomic number, the material density, and the material thickness. In this PhD thesis, our objective is to summarize a number of presentations and publications that are devoted to the computational aspects of muon tomography, the purpose of which is to characterize the target materials such as nuclear materials in diverse applications. We present our outcomes in a quantitative as well as in a qualitative format when/if necessary. First, we attempt to estimate the kinetic energy of the incoming muons by using the deflection angle through the detector layers fabricated from polyvinyl toluene. Secondly, in addition to the derivation of the triangular correlation, we determine the characteristic parameters such as the scattering angle, the muon absorption, and the muon displacement for the bulky nuclear waste barrels as well as the homogenized nuclear waste barrels. Finally, rather than using the vertical muons with either a constant energy or a uniform energy distribution, we try to sophisticate the muon sources by utilizing a restrictive plane and a discretized energy spectrum.https://www.ester.ee/record=b555893

Cosmic-ray tomography for border security

A key task for customs workers is the interception of hazardous, illegal and counterfeit items in order to protect the health and safety of citizens. However, it is estimated that only a small fraction of cargo is inspected and an even smaller fraction of trafficked goods are detected. Today, the most widely used technology for scanning vehicles, ranging from vans and trucks to railcars, is γ ray and X-ray radiography. New technologies are required to overcome current technological shortcomings, such as the inability to detect the target material composition, the usage of harmful ionising radiation sources and the resultant low throughput. Cosmic ray tomography (CRT) is a promising technology for cargo screening. Cosmic ray muons have average energies of around 10,000 times larger than a typical X-ray and therefore can penetrate relatively large and dense materials. By analysing muon scattering, it is possible to identify materials hidden inside shielding that is too thick or deep for other imaging methods. CRT is also completely passive, exploiting naturally occurring secondary cosmic radiation, and is therefore safe for humans and animals. Contrary to conventional X-ray- or γ -ray-based imaging techniques, CRT also allows material differentiation and anomaly localisation within the cargo or vehicle through the provision of 3D images. This article reviews the current state-of-the-art technology in CRT, critically assessing the strengths and weaknesses of the method, and suggesting further directions for development

Density imaging of volcanos with atmospheric muons

collaboration : TOMUVOLInternational audienceTheir capability to penetrate large depths of material renders high-energy atmospheric muons a unique probe for geophysical explorations. Provided the topography of the target is known, the measurement of the attenuation of the muon flux permits the cartography of matter density distributions revealing spatial and possibly also temporal variations in extended geological structures. A Collaboration between volcanologists, astroparticle- and particle physicists, TOMUVOL, was formed in 2009 to study tomographic muon imaging of volcanos with high-resolution tracking detectors. This contribution presents preparatory work towards muon tomography as well as flux measurements obtained after the first months of data taking at the Puy de Dˆome, an inactive lava dome volcano in the Massif Central in south-central France

An integrated geological-geophysical approach to subsurface interface reconstruction of muon tomography measurements in high alpine regions

Muon tomography is an imaging technique that emerged in the last decades. The principal concept is similar to X-ray tomography, where one determines the spatial distribution of material densities by means of penetrating photons. It differs from this well-known technology only by the type of particle. Muons are continuously produced in the Earth’s atmosphere when primary cosmic rays (mostly protons) interact with the atmosphere’s molecules. Depending on their energies these muons can penetrate materials up to several hundreds of metres (or even kilometres). Consequently, they have been used for the imaging of larger objects, including large geological objects such as volcanoes, caves and fault systems. This research project aimed at applying this technology to an alpine glacier in Central Switzerland to determine its bedrock geometry, and if possible, to gain information on the bedrock erosion mechanism. To this end, two major experimental studies have been conducted with the aim to reconstruct bedrock geometries of two different glaciers. Given this framework, I present in this thesis my contribution to the project in which I worked for 5 years. Most of the technological know-how of muon tomography still lies within physics institutes who were the key drivers in the development of this method. As the geophysical/geological community is nowadays an important user of this technology, it is important that also non-physicists familiarise themselves with the theory and concepts behind muon tomography. This can be seen as an effective method to bring more geoscientists to utilize this new technology for their own research. The first part of this thesis is designed to tackle this problem with a review article on the principles of muon tomography and a guide to best practice. A second important aspect is the reconstruction of the bedrock topography given muon flux measurements at various locations. Many to-date reconstruction algorithms include supplementary geological information such as density and/or compositional measurements only on the side. A probabilistic framework was successfully set up that allows for such additional data to be included into the inversion. This may be used to better constrain the bedrock geometry. Moreover, this flexible framework allows also for the inclusion of modelling errors in the physical models which may result in a more reliable estimate of the mean and standard deviation of the bedrock position. The third article is concerned with the determination of the effect of rock composition on the muon flux measurements. Researchers in the community use a made-up rock, called “standard-rock” in their calculations. Hitherto, it was unclear in which geological settings this is a valid assumption and in which the induced error becomes too large. Simulations that use this fantasy rock are performed and compared to simulations that use a more realistic rock model. It was found that for felsic rocks the standard-rock approximation is valid over all thickness ranges, while for mafic rocks and limestones this can lead to a serious bias if the rock is thicker than 300m

Sub-nanosecond Cherenkov photon detection for LHCb particle identification in high-occupancy conditions and semiconductor tracking for muon scattering tomography

The increase in luminosity during the LHC upgrade programme causes a challenging rise in track multiplicity and hit occupancy in the LHCb detector. In order to mitigate this effect, the use of photon detector hit time information is presented in the context of the Ring-Imaging Cherenkov (RICH) detectors. The application of a time gate in the FPGA of the digital readout board for the Upgrade Ia photon detector, which is being installed for LHC Run 3, is described. Data recorded during SPS charged particle beam tests using a 6.25 ns time gate show a reduction of up to a factor of four in asynchronous detector noise compared to the original 25ns readout. A time-walk correction based on the time-over- threshold is proposed. Using the LHCb simulation framework, the intrinsic time resolution of the RICH detectors is demonstrated to be less than 10 ps. This is particularly relevant for the LHCb Upgrade II, which is scheduled for the year 2030 in preparation for a further order- of-magnitude rise in luminosity. Methods of time gating and scaling of the signal amplitude in the RICH reconstruction likelihood maximisation algorithm are presented. The results show that, considering improvements in the time-resolution only, a photon detector with an approximately 50 ps resolution can achieve today’s particle ID performance in the high- luminosity LHC environment. In the second part of this thesis, the first published semiconductor tracker for cosmic-ray muon scattering tomography is presented. The tracker uses silicon strip sensors from the ATLAS Semiconductor Tracker (SCT) with an 80μm pitch. A novel electronic readout system for the sensors is designed, based on a scalable, inexpensive, flexible, FPGA-based solution. A high-precision mechanical structure with integrated cooling is built to align the SCT modules. This alignment is fine-tuned in software, and the tracker performance is compared with a Geant4 simulation. A scattering angle resolution compatible with 1.5 mrad at the 4 GeV average cosmic-ray muon energy is obtained. Data are recorded for plastic, iron and lead samples using 45000 muons. Images are reconstructed using the Angle Statistics Reconstruction algorithm, and demonstrate good contrast between low and high atomic number materials

Sensitivity and background estimates towards Phase-I of the COMET muon-to-electron conversion search

COMET is a future high-precision experiment searching for charged lepton flavour violation through the muon-to-electron conversion process. It aims to push the intensity frontier of particle physics by coupling an intense muon beam with cutting-edge detector technology. The first stage of the experiment, COMET Phase-I, is currently being assembled and will soon enter its data acquisition period. It plans to achieve a single event sensitivity to μ-e conversion in aluminium of 3.1x10⁻¹⁵. This thesis presents a study of the sensitivity and backgrounds of COMET Phase-I using the latest Monte Carlo simulation data produced. The background contribution from cosmic ray-induced atmospheric muons is estimated using a backward Monte Carlo approach, which allows computational resources to be focused on the most critical signal-mimicking events. Analysis of a μ-e conversion simulation sample suggests that COMET Phase-I will reach a single event sensitivity of 3.6x10⁻¹⁵ within 146 days of data acquisition. Our results suggest that, in that period, on the order of 10³ atmospheric muons will enter the detector system and produce an event similar enough to the conversion signal to pass all the signal selection criteria. Most of these events will be rejected by the Cosmic Ray Veto system, however, we expect at least 2.2 background events to sneak in unnoticed. It is vital for the conversion search that these events be discriminated from conversion electrons, for instance by using Cherenkov threshold counters to distinguish between muons and electrons or, alternatively, by developing a direction identification algorithm to reject some fraction of the μ⁺-induced events.Open Acces