Cosmic-ray muography

Lynkeos Technology Ltd is the first company in the UK to commercialise a muography system.  The Lynkeos Muon Imaging System was developed over a seven-year research and development programme undertaken by the Nuclear Physics group at the University of Glasgow in partnership with the UK National Nuclear Laboratory.  In total, over £4.8 million of funding was provided by Sellafield Ltd., on behalf of the UK Nuclear Decommissioning Authority, to develop a passive solution to one of the most complex challenges facing today’s society: the safe and cost-effective storage of legacy nuclear waste. In April 2017, Lynkeos Technology was awarded a £1.6 million First-Of-A-Kind (FOAK) Deployment of Innovation contract from Innovate UK to commercialise its Muon Imaging System.  As a result of this contract, which was successfully completed in March 2018, the first commercial muography system was deployed within the global nuclear industry.  This FOAK deployment on the Sellafield site has opened up the opportunity to image active waste samples for the first time.  As part of this yearlong contract, Lynkeos successfully imaged a 500-litre stainless-steel, concrete-filled Intermediate Level Waste drum that had been retrospectively filled with a 2cm-diameter, 3cm-long cylinder of uranium metal.  This was imaged to sub-centimetre resolution through 1m of concrete and steel. Since its formation in August 2016, Lynkeos Technology has received support from Innovate UK, Scottish Enterprise, EPSRC, STFC and the Royal Society of Edinburgh as well as its first commercial contract from a prominent UK Nuclear Industry organisation.

Long term monitoring of spent fuel stored in dry cask storage is currently achieved through the use of seals and surveillance. Muon tomography can provide direct imaging that may be useful in cases where what is known as continuity of knowledge (COK) has been lost using the former methods. Over the past several years a team from Los Alamos National Laboratory has been studying the use of muon scattering and stopping to examine spent fuel in dry cask storage. Data have been taken examining a Westinghouse MC-10 spent fuel cask partially loaded with Surry 15x15 PWR fuel assemblies located at the Idaho National Laboratory. The data demonstrate that muon scattering radiography can detect the missing fuel assemblies in this cask. 
Model, validated by this data, shows that tomographic reconstructions of the fuel can be obtained in relatively short exposures. Model fitting algorithms have been developed for dealing with data sets with limited angular that appear to work well. The data, modeling, and reconstruction methods developed during this work will be presented.

Lingacom Ltd is a commercial muon-imaging company, which is developing gas-based muon detectors and imaging algorithms for the detection of shielded nuclear material (SNM) and for mapping rocks and soil. For the detection of SNM, Lingacom Ltd focuses on a combined X-ray and muography solution, where a high-energy X-ray imaging system (a) clears most of the incoming cargo, (b) identifies specific regions of interest within large cargos, and (c) provides raw data for their internally-developed X-ray and muography imaging algorithm. This combination offers fast average throughput with detailed imaging of dense cargo. Lingacom Ltd focuses on muon-imaging systems specialized for scanning containers at sea ports and for scanning vehicles entering and exiting sensitive sites, such as nuclear power plants. For underground mapping they focus on developing borehole detectors that can fit within industry-standard boreholes in the field of civil engineering. Dr Harel will present the simulations of such detectors in several scenarios.

A common problem for the industry is the impact on operation performance due to variations in the wall thickness of critical facilities like pipes, boilers or blast furnaces. Due to the extreme conditions inside, the walls of these equipment suffer wear and the structural integrity is compromised. It is necessary to carry out preventive technical stops to measure the wall thickness, with a high economical and energetical costs. Muon tomography allows to explore and observe the interior of large objects, structures, and environments, without any contact or damage, and without having physical access to them. Muon Systems combines state-of-the-art detection technologies with innovative manufacturing and processing solutions, making the muon tomography a competitive and novel technology, that provides solutions at a scale never achieved by traditional tomographic systems. In this industrial environment, Muon Systems technology provides a clean and safe way to estimate the wall thickness with milimetric precision, without stopping the productive process and allowing a better planning of the technical stops, yielding large economical and energetic profits. As this is a harmless technique, muon tomography allows not only punctual inspection but also a good way to continuously monitor the interior of a critical facility. With the support of one of the biggest companies in the petrol and gas sector, Muon Systems is focused in the adaptation and development of muon tomography in industrial applications.

Muography is an imaging technique making use of natural cosmic muons to probe the inside of objects. These muons originate from the interaction of primary cosmic rays with the Earth atmosphere. Their large energy spectrum allows them to penetrate from a few meters to several hundred meters of stones, and their interactions with matter provide hints of its density distribution. Depending on the size of the object this distribution can be obtained by measuring either the angular deviation of muons or the absorption/transmission factors in different directions.  The main difficulty of muography is to cope with a modest muon flux, and therefore to build a large area but precise and robust instruments. Following the R&D made on gaseous, micromegas detectors for nuclear and particle physics, researchers have built at CEA/Irfu seven high-resolution muography instruments over the last three years. Three of them were deployed around the Khufu’s Pyramid in Egypt, within the ScanPyramids mission. In spite of extreme environmental conditions (temperature, dust, storms) the telescopes showed good performance and stability. After the discovery of a first cavity in 2016 on the North-East edge of the Pyramid, they participated in the discovery of the “ScanPyamids Big Void”, in 2017. This detection is the first ever of a deep structure of a pyramid from outside, and opens many more applications of HD muography in the coming years.

Muon imaging has found, during the last decades, a plethora of applications in many fields. This technique succeeds to infer the density distribution of inaccessible structures where conventional techniques cannot be used. The requirements of different applications demand specific implementations of the image reconstruction algorithms for either multiple scattering or absorption/transmission data analysis, noise-suppression filters and muon momentum estimators. The talk aims at presenting the results of image reconstruction techniques applied to simulated data of some representative applications. The effectiveness of the detection of shielded nuclear material hidden in scrap metal cargos is demonstrated using scattering tomography algorithms. This application requires fast object detection and optimal signal identification versus false positive alarms ratio. Therefore it requires proper image filtering techniques and a particle momentum estimation based on the muon trajectory behavior inside the detectors. Muon imaging capability to map the distribution of the materials inside a very large and dense structure like a blast furnace is probed using both muon scattering and absorption algorithms. Results are presented and compared. The long term stability monitoring of nuclear waste storage containers application is evaluated. This application requires much more relaxed acquisition time. Results obtained with simple algorithm based on weighted count of muons or more sophisticated absorption algorithms are presented.

The atmospheric muon flux transmittance through volcanoes  can be measured with muon telescopes deployed at various distances from the target (up to few kilometres). From this measurement a radiographic  (2D) image  of the edifice density structure is inferred provided that high energy, ballistic muons can be efficiently selected among all the charged particles measured by the telescopes [Ambrosino et al, 2015]. The muography  is potentially  high resolution imaging (better than 10 mrad x10 mrad) though the angular resolution is artificially degraded in order to preserve the resolution of the density measurement. This contribution presents  the first muographic imaging of Puy de Dôme  obtained with data taken from several locations between 2013 and 2018.  The methodological approach used to reconstruct the densities from  muon counts  was validated using data sets obtained with telescopes operated in different modes and deployed   both in surface and underground sites. The simulation and analysis chain can be reliably used to infer the potential of muographic measurements on any volcano of interest. The muography data taken on Puy de Dôme are not sufficient to attempt a tomographic reconstruction of the volcano, though they were already used to test in a robust way  geological models.   However, combined with high density  gravimetry data [Portal et al, 2016]  they offer  a first 3D map of the Puy de Dôme density, rather stable against different choices for  the regularisation of the inversion.  

In recent years, cosmic muons have been used successfully to obtain information on the internal structure of volcanic cones. A new generation of detectors has been specially developed to operate in outdoor environments, with low power consumption, reliable, remotely controllable and easily transportable and installable. This technique promises to be useful also for applications in archeology and civil engineering. It can be used together with other geological prospecting methods or alternatively to them when the usual methods can not be used profitably. In particular, the muon radiography is able to identify cavities and anomalies of the density present in the ground, exploring large volumes of soil above the detector. In order to understand the potential of the method in this field, some measurements were carried out at the natural laboratory of Mt. Echia, in the city of Naples, Italy.  In the past centuries, many cavities have been created by digging in the yellow tuff of Monte Echia, the site of the ancient Greek city of Partenope, the first settlement of the current city of Naples (VIII century BC). A muon tracker was installed in two different positions, under a tuff thickness of about 40m, obtaining muographic images of the cavities visible from the detector. The known cavities have been carefully modeled and their muographic images have been reproduced. The agreement between measured data and expected results is excellent. Signals of the presence of unknown cavities are observed. Furthermore, the method also provided a map of average absolute density of the hill. The excellent results obtained have demonstrated the ability of the muographical method to operate even in a very urbanized environment, where many of the ordinary geological prospecting systems often fail to operate in a useful way.

Humans have viewed volcanoes as both as a threat, due to their potential to cause major disasters, as well as appreciating their mysterious beauty. The 20th century developments of geophysics, geochemistry, petrology, and mineralogy have enriched people’s knowledge of Earth, and recently, predicting when the eruption starts has become possible by observing its precursors. However, prediction of “how the eruption follows the sequence, and when it will end” are developing and ongoing efforts. Volcano research has long been dominated by classical mechanics, largely disregarding the potential of particle physics to augment existing techniques. The purpose of this talk is to present a potential of a new imaging technique called muography to apply to studying geodynamics of volcanoes. High-energy muons that are produced via the reaction between primary cosmic rays and the Earth’s atmosphere can be used as a probe to explore the density distribution in gigantic objects including shallow parts of the Earth's crust. Muography has the potential to serve as a useful paradigm to transform our understanding of underground structures as the X-ray transformed our understanding of medicine and the body. Existing results for various volcanoes will be discussed here, and an outlook regarding anticipated future observations will be briefly discussed.

* Abstract was provided by Professor Hiroyuki Tanaka, University of Tokyo, Japan

Carbon capture and storage is a transition technology from a past and present fueled by coal, oil and gas and a, hoped for, future dominated by renewable energy sources.  The technology involves the capture of carbon dioxide emissions from fossil fuel power stations and other point sources, compression of the CO2 into a fluid, transporting it and then injecting it deep beneath the Earth’s surface into depleted petroleum reservoirs and other porous formations. Once injected, the CO2 must be monitored to ensure none leaks back to surface.  A variety of methods have been deployed to monitor the CO2 storage site and many such methods have been adapted from oilfield practice.  However, such methods are commonly indirect, episodic, require active signal generation and remain expensive throughout the monitoring period that may last for hundreds of years. Models were built to simulate CO2 storage conditions and the potential for using variations in cosmic-ray muon attenuation as a function of CO2 abundance tested.  From this we developed a passive, continuous monitoring method for CO2 storage sites using muon tomography, the tools for which can be deployed during the active drilling phase (development) of the storage site.  To do this it was necessary to develop a muon detector that could be used in the hostile environment (saline, high temperature) of the well bore.  A prototype detector has been built and tested at the 1.1km deep Boulby potash mine on the NE coast of England. 

Imaging subsurface rock formations or geological objects like oil and gas reservoirs, mineral deposits, cavities or even magmatic plumbing systems under active volcanoes has been for many years a major quest of geophysicists and geologists. Since these objects cannot be observed directly, different indirect methods have been developed. They are all based on variations of certain physical properties of the subsurface materials that can be detected from the ground surface or from boreholes. To determine the density distribution, a new imaging technique using cosmic ray muon detectors deployed in a borehole has been developed and a first prototype of borehole muon detector successfully tested. In addition to providing a static image of the subsurface density in three dimensions (or 3D tomography), borehole muography can also inform on the variations of density with time which became recently of major importance. The injection of large volumes of fluids, mainly water and CO2, in subsurface reservoirs is indeed increasingly performed in various applications (e.g., aquifer storage and recovery, waste water disposal, enhanced oil recovery, carbon sequestration). This raises several concerns about the mechanical integrity of the reservoirs themselves and their surroundings. Determining the field scale induced displacement of fluids and the temporal and spatial deformations of the ground surface is thus a priority. Finally, to improve imaging of 3D subsurface structures, a combination of seismic data, gravity data, and muons can be used and this promises to be a powerful way to improve spatial resolution and reduce uncertainty.

CRM Geotomography Technologies Inc. (CRM) is a pioneer in applying muon tomography technology to resource exploration and monitoring, which we call muon geotomography. While the concept of applying muon tomography in exploration geophysics has been in the literature for decades, it has only become practical and practiced this decade.  CRM has deployed muon geotomography surveys in underground mines to image dense ore bodies such as volcanogenic massive sulphide and mississippi valley type polymetallic deposits, as well as uranium deposits, among others.  Robust, field-proven muon detectors have been developed by CRM for brownfield (existing mine) geophysical surveys, and CRM has also demonstrated joint inversion capability with gravimetric and assay data.  Although initial projects focused on brownfield mineral exploration, this 3D density imaging and monitoring technique has applications in greenfield mineral exploration, oil and gas, and industrial monitoring and security applications. This presentation will review some of CRM's recent work in muon geotomography, as well as a preview of our ongoing work for developing next-generation detectors, and simulations of unpublished applications.