<p> Nuclear waste management and nonproliferation are among the critical tasks to be addressed for the advancement of nuclear energy in the United States. In this regard, monitoring spent nuclear fuel (SNF) and special nuclear materials (SNM) is important to continue reliable stewardship of SNF management and prevent SNM proliferation. Cosmic ray muons have been used for imaging large and dense objects, e.g., SNF dry casks, the Fukushima Daiichi unit-1 reactor, and the great pyramid of Giza. Despite their potential and success, the wide application of cosmic ray muons is limited by the naturally low intensity at sea level, approximately 10⁴ m^-2min^-1. For example, when imaging large objects, time consuming measurements typically in the order of several days or even weeks, are frequently needed to collect a statistically significant amount of muon samples to reconstruct images using muon tomography. However, when scanning time is of essence, e.g., treaty verification, low resolution imaging can result in potentially undetected diversion of nuclear materials.</p> <p>To maximize the utilizability of cosmic ray muons in engineering and physics applications, two important quantities–scattering angle and momentum–must be measured. Although many studies have demonstrated that there are significant benefits when measuring momentum in muon applications, measuring both the muon scattering angle and muon momentum in the field remains a challenge. To fill this critical gap, a novel concept using multi-layer pressurized gas Cherenkov radiators that is fieldable to allow muon momentum measurement in the field is presented in this dissertation. The proposed Cherenkov muon spectrometer is: (i) accurate (~90%) in classifying muon momentum, (ii) lightweight (< 10 kg) for easy transport and deployment in the field, (iii) compact (< 1 m³), and (iv) easily coupled with existing muon tomographic systems. Although muon momentum measurement resolution of spectrometers used in high energy physics laboratories, such as CMS or ATLAS of LHC at CERN, is less than 5% for low energy muons, these spectrometers typically (i) use bulky and large solenoidal or toroidal magnets and (ii) interfere with muon trajectories to measure momentum. These characteristics make them unsuitable for field deployment.</p> <p>In this work, the feasibility of using the proposed Cherenkov muon spectrometer coupled with current muon tomographic systems is explored and evaluated using Monte Carlo simulations and reconstruction algorithms. It is shown the use of the proposed Cherenkov muon spectrometer has the potential to improve muon tomographic imaging resolution or reduce measurement time by a factor of 10 or more when used to identify a missing fuel assembly from a SNF dry cask. In addition, a new imaging algorithm is developed that integrates muon momentum and muon scattering without significantly increasing computational cost. Advances in momentum-integrated muon tomography have the potential to improve monitoring and imaging efficiency in various nuclear engineering applications. For example, it can expand current capabilities to continue reliable stewardship in nuclear material management, i.e., Continuity of Knowledge, and prevent SNM proliferation to unauthorized states and parties. The benefit of such an approach is a compact, lightweight, and portable spectrometer that can be deployed in the field to improve existing or explore new engineering applications: muon tomography, geological studies, and cosmic radiation measurement in space.</p>

<p>Recently, the use of cosmic ray muons in critical national security applications, e.g., nuclear nonproliferation and safeguards verification, has gained attention due to unique muon properties such as high energy and low attenuation even in very dense materials. Applications where muon tomography has been demonstrated include cargo screening for detection of special nuclear materials smuggling, source localization, material identification, determination of nuclear fuel debris location in nuclear reactors, etc. However, muon image reconstruction techniques are still limited in resolution mostly due to multiple Coulombscattering (MCS) within the target object. Improving and expanding muon tomography would require development of efficient & flexible physics-based algorithms to model the MCS process and accurately estimate the most probable trajectory of a muon as it traverses the target object. The present study introduces a novel algorithmic approach that utilizes Bayesian probability theory and a Gaussian approximation of MCS to estimate the most probable path of cosmic ray muons as they traverse uniform media.</p> <p>Using GEANT4, an investigation was conducted involving the trajectory of 10,000 muon particles that underwent bombardment from a point source parallel to the x-axis. The proposed algorithm was assessed through four types of simulations. In the first type, muons with energies of 1 GeV, 3 GeV, 10 GeV, and 100 GeV were utilized to evaluate the algorithms’ performance and accuracy. The second type of simulation involved the use of target cubes composed of different materials, including aluminum, iron, lead, and uranium. These simulations specifically focused on muons with an energy of 3 GeV. Next, the third type of simulation entailed employing target cubes with varying lengths, such as 10 cm, 20 cm, 40 cm, and 80 cm, specifically using muons with an energy of 3 GeV and a uranium target. Lastly, all the previous simulations were revised to accommodate a source of poly-energetic muons. This revision was undertaken to create a more realistic source scenario that aligns with the distribution of muon energies encountered in real-world situations.</p> <p>The results demonstrate significant improvements in precision and muon flux utilization when comparing different algorithms. The Generalized Muon Trajectory Estimation (GMTE) algorithm shows around 50% improvement in precision compared to currently used Straight Line Path (SLP) algorithm across all test scenarios. Additionally, GMTE algorithm exhibits around 38% improvement in precision compared to the extensively used Point of Closest Approach (PoCA) algorithm. Similarly for both mono and poly energetic source of muons, the GMTE algorithm shows 10%-35% increase in muon flux utilization for high Z materials and a 10%-15% increase for medium Z materials compared to the PoCA algorithm. Similarly, it demonstrates 6%-9% increase in muon flux utilization for both medium and high Z materials compared to the SLP algorithm across all test scenarios. These results highlight the enhanced performance and efficiency of GMTE algorithm in comparison to SLP and PoCA algorithms.</p> <p>Through these extensive simulations, our objective was to comprehensively evaluate the performance and effectiveness of the proposed algorithm across a range of variables, including energy levels, materials, and target geometries. The findings of our study demonstrate that the utilization of these algorithm enables improved resolution and reduced measurement time for cosmic ray muons when compared with current SLP and PoCA algorithm.</p>